| <?xml version="1.0" encoding="UTF-8"?> |
| <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" |
| "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> |
| |
| <book id="drmDevelopersGuide"> |
| <bookinfo> |
| <title>Linux DRM Developer's Guide</title> |
| |
| <authorgroup> |
| <author> |
| <firstname>Jesse</firstname> |
| <surname>Barnes</surname> |
| <contrib>Initial version</contrib> |
| <affiliation> |
| <orgname>Intel Corporation</orgname> |
| <address> |
| <email>jesse.barnes@intel.com</email> |
| </address> |
| </affiliation> |
| </author> |
| <author> |
| <firstname>Laurent</firstname> |
| <surname>Pinchart</surname> |
| <contrib>Driver internals</contrib> |
| <affiliation> |
| <orgname>Ideas on board SPRL</orgname> |
| <address> |
| <email>laurent.pinchart@ideasonboard.com</email> |
| </address> |
| </affiliation> |
| </author> |
| </authorgroup> |
| |
| <copyright> |
| <year>2008-2009</year> |
| <year>2012</year> |
| <holder>Intel Corporation</holder> |
| <holder>Laurent Pinchart</holder> |
| </copyright> |
| |
| <legalnotice> |
| <para> |
| The contents of this file may be used under the terms of the GNU |
| General Public License version 2 (the "GPL") as distributed in |
| the kernel source COPYING file. |
| </para> |
| </legalnotice> |
| |
| <revhistory> |
| <!-- Put document revisions here, newest first. --> |
| <revision> |
| <revnumber>1.0</revnumber> |
| <date>2012-07-13</date> |
| <authorinitials>LP</authorinitials> |
| <revremark>Added extensive documentation about driver internals. |
| </revremark> |
| </revision> |
| </revhistory> |
| </bookinfo> |
| |
| <toc></toc> |
| |
| <!-- Introduction --> |
| |
| <chapter id="drmIntroduction"> |
| <title>Introduction</title> |
| <para> |
| The Linux DRM layer contains code intended to support the needs |
| of complex graphics devices, usually containing programmable |
| pipelines well suited to 3D graphics acceleration. Graphics |
| drivers in the kernel may make use of DRM functions to make |
| tasks like memory management, interrupt handling and DMA easier, |
| and provide a uniform interface to applications. |
| </para> |
| <para> |
| A note on versions: this guide covers features found in the DRM |
| tree, including the TTM memory manager, output configuration and |
| mode setting, and the new vblank internals, in addition to all |
| the regular features found in current kernels. |
| </para> |
| <para> |
| [Insert diagram of typical DRM stack here] |
| </para> |
| </chapter> |
| |
| <!-- Internals --> |
| |
| <chapter id="drmInternals"> |
| <title>DRM Internals</title> |
| <para> |
| This chapter documents DRM internals relevant to driver authors |
| and developers working to add support for the latest features to |
| existing drivers. |
| </para> |
| <para> |
| First, we go over some typical driver initialization |
| requirements, like setting up command buffers, creating an |
| initial output configuration, and initializing core services. |
| Subsequent sections cover core internals in more detail, |
| providing implementation notes and examples. |
| </para> |
| <para> |
| The DRM layer provides several services to graphics drivers, |
| many of them driven by the application interfaces it provides |
| through libdrm, the library that wraps most of the DRM ioctls. |
| These include vblank event handling, memory |
| management, output management, framebuffer management, command |
| submission & fencing, suspend/resume support, and DMA |
| services. |
| </para> |
| |
| <!-- Internals: driver init --> |
| |
| <sect1> |
| <title>Driver Initialization</title> |
| <para> |
| At the core of every DRM driver is a <structname>drm_driver</structname> |
| structure. Drivers typically statically initialize a drm_driver structure, |
| and then pass it to one of the <function>drm_*_init()</function> functions |
| to register it with the DRM subsystem. |
| </para> |
| <para> |
| The <structname>drm_driver</structname> structure contains static |
| information that describes the driver and features it supports, and |
| pointers to methods that the DRM core will call to implement the DRM API. |
| We will first go through the <structname>drm_driver</structname> static |
| information fields, and will then describe individual operations in |
| details as they get used in later sections. |
| </para> |
| <sect2> |
| <title>Driver Information</title> |
| <sect3> |
| <title>Driver Features</title> |
| <para> |
| Drivers inform the DRM core about their requirements and supported |
| features by setting appropriate flags in the |
| <structfield>driver_features</structfield> field. Since those flags |
| influence the DRM core behaviour since registration time, most of them |
| must be set to registering the <structname>drm_driver</structname> |
| instance. |
| </para> |
| <synopsis>u32 driver_features;</synopsis> |
| <variablelist> |
| <title>Driver Feature Flags</title> |
| <varlistentry> |
| <term>DRIVER_USE_AGP</term> |
| <listitem><para> |
| Driver uses AGP interface, the DRM core will manage AGP resources. |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRIVER_REQUIRE_AGP</term> |
| <listitem><para> |
| Driver needs AGP interface to function. AGP initialization failure |
| will become a fatal error. |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRIVER_PCI_DMA</term> |
| <listitem><para> |
| Driver is capable of PCI DMA, mapping of PCI DMA buffers to |
| userspace will be enabled. Deprecated. |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRIVER_SG</term> |
| <listitem><para> |
| Driver can perform scatter/gather DMA, allocation and mapping of |
| scatter/gather buffers will be enabled. Deprecated. |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRIVER_HAVE_DMA</term> |
| <listitem><para> |
| Driver supports DMA, the userspace DMA API will be supported. |
| Deprecated. |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRIVER_HAVE_IRQ</term><term>DRIVER_IRQ_SHARED</term> |
| <listitem><para> |
| DRIVER_HAVE_IRQ indicates whether the driver has an IRQ handler |
| managed by the DRM Core. The core will support simple IRQ handler |
| installation when the flag is set. The installation process is |
| described in <xref linkend="drm-irq-registration"/>.</para> |
| <para>DRIVER_IRQ_SHARED indicates whether the device & handler |
| support shared IRQs (note that this is required of PCI drivers). |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRIVER_GEM</term> |
| <listitem><para> |
| Driver use the GEM memory manager. |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRIVER_MODESET</term> |
| <listitem><para> |
| Driver supports mode setting interfaces (KMS). |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRIVER_PRIME</term> |
| <listitem><para> |
| Driver implements DRM PRIME buffer sharing. |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRIVER_RENDER</term> |
| <listitem><para> |
| Driver supports dedicated render nodes. |
| </para></listitem> |
| </varlistentry> |
| </variablelist> |
| </sect3> |
| <sect3> |
| <title>Major, Minor and Patchlevel</title> |
| <synopsis>int major; |
| int minor; |
| int patchlevel;</synopsis> |
| <para> |
| The DRM core identifies driver versions by a major, minor and patch |
| level triplet. The information is printed to the kernel log at |
| initialization time and passed to userspace through the |
| DRM_IOCTL_VERSION ioctl. |
| </para> |
| <para> |
| The major and minor numbers are also used to verify the requested driver |
| API version passed to DRM_IOCTL_SET_VERSION. When the driver API changes |
| between minor versions, applications can call DRM_IOCTL_SET_VERSION to |
| select a specific version of the API. If the requested major isn't equal |
| to the driver major, or the requested minor is larger than the driver |
| minor, the DRM_IOCTL_SET_VERSION call will return an error. Otherwise |
| the driver's set_version() method will be called with the requested |
| version. |
| </para> |
| </sect3> |
| <sect3> |
| <title>Name, Description and Date</title> |
| <synopsis>char *name; |
| char *desc; |
| char *date;</synopsis> |
| <para> |
| The driver name is printed to the kernel log at initialization time, |
| used for IRQ registration and passed to userspace through |
| DRM_IOCTL_VERSION. |
| </para> |
| <para> |
| The driver description is a purely informative string passed to |
| userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by |
| the kernel. |
| </para> |
| <para> |
| The driver date, formatted as YYYYMMDD, is meant to identify the date of |
| the latest modification to the driver. However, as most drivers fail to |
| update it, its value is mostly useless. The DRM core prints it to the |
| kernel log at initialization time and passes it to userspace through the |
| DRM_IOCTL_VERSION ioctl. |
| </para> |
| </sect3> |
| </sect2> |
| <sect2> |
| <title>Driver Load</title> |
| <para> |
| The <methodname>load</methodname> method is the driver and device |
| initialization entry point. The method is responsible for allocating and |
| initializing driver private data, specifying supported performance |
| counters, performing resource allocation and mapping (e.g. acquiring |
| clocks, mapping registers or allocating command buffers), initializing |
| the memory manager (<xref linkend="drm-memory-management"/>), installing |
| the IRQ handler (<xref linkend="drm-irq-registration"/>), setting up |
| vertical blanking handling (<xref linkend="drm-vertical-blank"/>), mode |
| setting (<xref linkend="drm-mode-setting"/>) and initial output |
| configuration (<xref linkend="drm-kms-init"/>). |
| </para> |
| <note><para> |
| If compatibility is a concern (e.g. with drivers converted over from |
| User Mode Setting to Kernel Mode Setting), care must be taken to prevent |
| device initialization and control that is incompatible with currently |
| active userspace drivers. For instance, if user level mode setting |
| drivers are in use, it would be problematic to perform output discovery |
| & configuration at load time. Likewise, if user-level drivers |
| unaware of memory management are in use, memory management and command |
| buffer setup may need to be omitted. These requirements are |
| driver-specific, and care needs to be taken to keep both old and new |
| applications and libraries working. |
| </para></note> |
| <synopsis>int (*load) (struct drm_device *, unsigned long flags);</synopsis> |
| <para> |
| The method takes two arguments, a pointer to the newly created |
| <structname>drm_device</structname> and flags. The flags are used to |
| pass the <structfield>driver_data</structfield> field of the device id |
| corresponding to the device passed to <function>drm_*_init()</function>. |
| Only PCI devices currently use this, USB and platform DRM drivers have |
| their <methodname>load</methodname> method called with flags to 0. |
| </para> |
| <sect3> |
| <title>Driver Private & Performance Counters</title> |
| <para> |
| The driver private hangs off the main |
| <structname>drm_device</structname> structure and can be used for |
| tracking various device-specific bits of information, like register |
| offsets, command buffer status, register state for suspend/resume, etc. |
| At load time, a driver may simply allocate one and set |
| <structname>drm_device</structname>.<structfield>dev_priv</structfield> |
| appropriately; it should be freed and |
| <structname>drm_device</structname>.<structfield>dev_priv</structfield> |
| set to NULL when the driver is unloaded. |
| </para> |
| <para> |
| DRM supports several counters which were used for rough performance |
| characterization. This stat counter system is deprecated and should not |
| be used. If performance monitoring is desired, the developer should |
| investigate and potentially enhance the kernel perf and tracing |
| infrastructure to export GPU related performance information for |
| consumption by performance monitoring tools and applications. |
| </para> |
| </sect3> |
| <sect3 id="drm-irq-registration"> |
| <title>IRQ Registration</title> |
| <para> |
| The DRM core tries to facilitate IRQ handler registration and |
| unregistration by providing <function>drm_irq_install</function> and |
| <function>drm_irq_uninstall</function> functions. Those functions only |
| support a single interrupt per device, devices that use more than one |
| IRQs need to be handled manually. |
| </para> |
| <sect4> |
| <title>Managed IRQ Registration</title> |
| <para> |
| Both the <function>drm_irq_install</function> and |
| <function>drm_irq_uninstall</function> functions get the device IRQ by |
| calling <function>drm_dev_to_irq</function>. This inline function will |
| call a bus-specific operation to retrieve the IRQ number. For platform |
| devices, <function>platform_get_irq</function>(..., 0) is used to |
| retrieve the IRQ number. |
| </para> |
| <para> |
| <function>drm_irq_install</function> starts by calling the |
| <methodname>irq_preinstall</methodname> driver operation. The operation |
| is optional and must make sure that the interrupt will not get fired by |
| clearing all pending interrupt flags or disabling the interrupt. |
| </para> |
| <para> |
| The IRQ will then be requested by a call to |
| <function>request_irq</function>. If the DRIVER_IRQ_SHARED driver |
| feature flag is set, a shared (IRQF_SHARED) IRQ handler will be |
| requested. |
| </para> |
| <para> |
| The IRQ handler function must be provided as the mandatory irq_handler |
| driver operation. It will get passed directly to |
| <function>request_irq</function> and thus has the same prototype as all |
| IRQ handlers. It will get called with a pointer to the DRM device as the |
| second argument. |
| </para> |
| <para> |
| Finally the function calls the optional |
| <methodname>irq_postinstall</methodname> driver operation. The operation |
| usually enables interrupts (excluding the vblank interrupt, which is |
| enabled separately), but drivers may choose to enable/disable interrupts |
| at a different time. |
| </para> |
| <para> |
| <function>drm_irq_uninstall</function> is similarly used to uninstall an |
| IRQ handler. It starts by waking up all processes waiting on a vblank |
| interrupt to make sure they don't hang, and then calls the optional |
| <methodname>irq_uninstall</methodname> driver operation. The operation |
| must disable all hardware interrupts. Finally the function frees the IRQ |
| by calling <function>free_irq</function>. |
| </para> |
| </sect4> |
| <sect4> |
| <title>Manual IRQ Registration</title> |
| <para> |
| Drivers that require multiple interrupt handlers can't use the managed |
| IRQ registration functions. In that case IRQs must be registered and |
| unregistered manually (usually with the <function>request_irq</function> |
| and <function>free_irq</function> functions, or their devm_* equivalent). |
| </para> |
| <para> |
| When manually registering IRQs, drivers must not set the DRIVER_HAVE_IRQ |
| driver feature flag, and must not provide the |
| <methodname>irq_handler</methodname> driver operation. They must set the |
| <structname>drm_device</structname> <structfield>irq_enabled</structfield> |
| field to 1 upon registration of the IRQs, and clear it to 0 after |
| unregistering the IRQs. |
| </para> |
| </sect4> |
| </sect3> |
| <sect3> |
| <title>Memory Manager Initialization</title> |
| <para> |
| Every DRM driver requires a memory manager which must be initialized at |
| load time. DRM currently contains two memory managers, the Translation |
| Table Manager (TTM) and the Graphics Execution Manager (GEM). |
| This document describes the use of the GEM memory manager only. See |
| <xref linkend="drm-memory-management"/> for details. |
| </para> |
| </sect3> |
| <sect3> |
| <title>Miscellaneous Device Configuration</title> |
| <para> |
| Another task that may be necessary for PCI devices during configuration |
| is mapping the video BIOS. On many devices, the VBIOS describes device |
| configuration, LCD panel timings (if any), and contains flags indicating |
| device state. Mapping the BIOS can be done using the pci_map_rom() call, |
| a convenience function that takes care of mapping the actual ROM, |
| whether it has been shadowed into memory (typically at address 0xc0000) |
| or exists on the PCI device in the ROM BAR. Note that after the ROM has |
| been mapped and any necessary information has been extracted, it should |
| be unmapped; on many devices, the ROM address decoder is shared with |
| other BARs, so leaving it mapped could cause undesired behaviour like |
| hangs or memory corruption. |
| <!--!Fdrivers/pci/rom.c pci_map_rom--> |
| </para> |
| </sect3> |
| </sect2> |
| </sect1> |
| |
| <!-- Internals: memory management --> |
| |
| <sect1 id="drm-memory-management"> |
| <title>Memory management</title> |
| <para> |
| Modern Linux systems require large amount of graphics memory to store |
| frame buffers, textures, vertices and other graphics-related data. Given |
| the very dynamic nature of many of that data, managing graphics memory |
| efficiently is thus crucial for the graphics stack and plays a central |
| role in the DRM infrastructure. |
| </para> |
| <para> |
| The DRM core includes two memory managers, namely Translation Table Maps |
| (TTM) and Graphics Execution Manager (GEM). TTM was the first DRM memory |
| manager to be developed and tried to be a one-size-fits-them all |
| solution. It provides a single userspace API to accommodate the need of |
| all hardware, supporting both Unified Memory Architecture (UMA) devices |
| and devices with dedicated video RAM (i.e. most discrete video cards). |
| This resulted in a large, complex piece of code that turned out to be |
| hard to use for driver development. |
| </para> |
| <para> |
| GEM started as an Intel-sponsored project in reaction to TTM's |
| complexity. Its design philosophy is completely different: instead of |
| providing a solution to every graphics memory-related problems, GEM |
| identified common code between drivers and created a support library to |
| share it. GEM has simpler initialization and execution requirements than |
| TTM, but has no video RAM management capabitilies and is thus limited to |
| UMA devices. |
| </para> |
| <sect2> |
| <title>The Translation Table Manager (TTM)</title> |
| <para> |
| TTM design background and information belongs here. |
| </para> |
| <sect3> |
| <title>TTM initialization</title> |
| <warning><para>This section is outdated.</para></warning> |
| <para> |
| Drivers wishing to support TTM must fill out a drm_bo_driver |
| structure. The structure contains several fields with function |
| pointers for initializing the TTM, allocating and freeing memory, |
| waiting for command completion and fence synchronization, and memory |
| migration. See the radeon_ttm.c file for an example of usage. |
| </para> |
| <para> |
| The ttm_global_reference structure is made up of several fields: |
| </para> |
| <programlisting> |
| struct ttm_global_reference { |
| enum ttm_global_types global_type; |
| size_t size; |
| void *object; |
| int (*init) (struct ttm_global_reference *); |
| void (*release) (struct ttm_global_reference *); |
| }; |
| </programlisting> |
| <para> |
| There should be one global reference structure for your memory |
| manager as a whole, and there will be others for each object |
| created by the memory manager at runtime. Your global TTM should |
| have a type of TTM_GLOBAL_TTM_MEM. The size field for the global |
| object should be sizeof(struct ttm_mem_global), and the init and |
| release hooks should point at your driver-specific init and |
| release routines, which probably eventually call |
| ttm_mem_global_init and ttm_mem_global_release, respectively. |
| </para> |
| <para> |
| Once your global TTM accounting structure is set up and initialized |
| by calling ttm_global_item_ref() on it, |
| you need to create a buffer object TTM to |
| provide a pool for buffer object allocation by clients and the |
| kernel itself. The type of this object should be TTM_GLOBAL_TTM_BO, |
| and its size should be sizeof(struct ttm_bo_global). Again, |
| driver-specific init and release functions may be provided, |
| likely eventually calling ttm_bo_global_init() and |
| ttm_bo_global_release(), respectively. Also, like the previous |
| object, ttm_global_item_ref() is used to create an initial reference |
| count for the TTM, which will call your initialization function. |
| </para> |
| </sect3> |
| </sect2> |
| <sect2 id="drm-gem"> |
| <title>The Graphics Execution Manager (GEM)</title> |
| <para> |
| The GEM design approach has resulted in a memory manager that doesn't |
| provide full coverage of all (or even all common) use cases in its |
| userspace or kernel API. GEM exposes a set of standard memory-related |
| operations to userspace and a set of helper functions to drivers, and let |
| drivers implement hardware-specific operations with their own private API. |
| </para> |
| <para> |
| The GEM userspace API is described in the |
| <ulink url="http://lwn.net/Articles/283798/"><citetitle>GEM - the Graphics |
| Execution Manager</citetitle></ulink> article on LWN. While slightly |
| outdated, the document provides a good overview of the GEM API principles. |
| Buffer allocation and read and write operations, described as part of the |
| common GEM API, are currently implemented using driver-specific ioctls. |
| </para> |
| <para> |
| GEM is data-agnostic. It manages abstract buffer objects without knowing |
| what individual buffers contain. APIs that require knowledge of buffer |
| contents or purpose, such as buffer allocation or synchronization |
| primitives, are thus outside of the scope of GEM and must be implemented |
| using driver-specific ioctls. |
| </para> |
| <para> |
| On a fundamental level, GEM involves several operations: |
| <itemizedlist> |
| <listitem>Memory allocation and freeing</listitem> |
| <listitem>Command execution</listitem> |
| <listitem>Aperture management at command execution time</listitem> |
| </itemizedlist> |
| Buffer object allocation is relatively straightforward and largely |
| provided by Linux's shmem layer, which provides memory to back each |
| object. |
| </para> |
| <para> |
| Device-specific operations, such as command execution, pinning, buffer |
| read & write, mapping, and domain ownership transfers are left to |
| driver-specific ioctls. |
| </para> |
| <sect3> |
| <title>GEM Initialization</title> |
| <para> |
| Drivers that use GEM must set the DRIVER_GEM bit in the struct |
| <structname>drm_driver</structname> |
| <structfield>driver_features</structfield> field. The DRM core will |
| then automatically initialize the GEM core before calling the |
| <methodname>load</methodname> operation. Behind the scene, this will |
| create a DRM Memory Manager object which provides an address space |
| pool for object allocation. |
| </para> |
| <para> |
| In a KMS configuration, drivers need to allocate and initialize a |
| command ring buffer following core GEM initialization if required by |
| the hardware. UMA devices usually have what is called a "stolen" |
| memory region, which provides space for the initial framebuffer and |
| large, contiguous memory regions required by the device. This space is |
| typically not managed by GEM, and must be initialized separately into |
| its own DRM MM object. |
| </para> |
| </sect3> |
| <sect3> |
| <title>GEM Objects Creation</title> |
| <para> |
| GEM splits creation of GEM objects and allocation of the memory that |
| backs them in two distinct operations. |
| </para> |
| <para> |
| GEM objects are represented by an instance of struct |
| <structname>drm_gem_object</structname>. Drivers usually need to extend |
| GEM objects with private information and thus create a driver-specific |
| GEM object structure type that embeds an instance of struct |
| <structname>drm_gem_object</structname>. |
| </para> |
| <para> |
| To create a GEM object, a driver allocates memory for an instance of its |
| specific GEM object type and initializes the embedded struct |
| <structname>drm_gem_object</structname> with a call to |
| <function>drm_gem_object_init</function>. The function takes a pointer to |
| the DRM device, a pointer to the GEM object and the buffer object size |
| in bytes. |
| </para> |
| <para> |
| GEM uses shmem to allocate anonymous pageable memory. |
| <function>drm_gem_object_init</function> will create an shmfs file of |
| the requested size and store it into the struct |
| <structname>drm_gem_object</structname> <structfield>filp</structfield> |
| field. The memory is used as either main storage for the object when the |
| graphics hardware uses system memory directly or as a backing store |
| otherwise. |
| </para> |
| <para> |
| Drivers are responsible for the actual physical pages allocation by |
| calling <function>shmem_read_mapping_page_gfp</function> for each page. |
| Note that they can decide to allocate pages when initializing the GEM |
| object, or to delay allocation until the memory is needed (for instance |
| when a page fault occurs as a result of a userspace memory access or |
| when the driver needs to start a DMA transfer involving the memory). |
| </para> |
| <para> |
| Anonymous pageable memory allocation is not always desired, for instance |
| when the hardware requires physically contiguous system memory as is |
| often the case in embedded devices. Drivers can create GEM objects with |
| no shmfs backing (called private GEM objects) by initializing them with |
| a call to <function>drm_gem_private_object_init</function> instead of |
| <function>drm_gem_object_init</function>. Storage for private GEM |
| objects must be managed by drivers. |
| </para> |
| <para> |
| Drivers that do not need to extend GEM objects with private information |
| can call the <function>drm_gem_object_alloc</function> function to |
| allocate and initialize a struct <structname>drm_gem_object</structname> |
| instance. The GEM core will call the optional driver |
| <methodname>gem_init_object</methodname> operation after initializing |
| the GEM object with <function>drm_gem_object_init</function>. |
| <synopsis>int (*gem_init_object) (struct drm_gem_object *obj);</synopsis> |
| </para> |
| <para> |
| No alloc-and-init function exists for private GEM objects. |
| </para> |
| </sect3> |
| <sect3> |
| <title>GEM Objects Lifetime</title> |
| <para> |
| All GEM objects are reference-counted by the GEM core. References can be |
| acquired and release by <function>calling drm_gem_object_reference</function> |
| and <function>drm_gem_object_unreference</function> respectively. The |
| caller must hold the <structname>drm_device</structname> |
| <structfield>struct_mutex</structfield> lock. As a convenience, GEM |
| provides the <function>drm_gem_object_reference_unlocked</function> and |
| <function>drm_gem_object_unreference_unlocked</function> functions that |
| can be called without holding the lock. |
| </para> |
| <para> |
| When the last reference to a GEM object is released the GEM core calls |
| the <structname>drm_driver</structname> |
| <methodname>gem_free_object</methodname> operation. That operation is |
| mandatory for GEM-enabled drivers and must free the GEM object and all |
| associated resources. |
| </para> |
| <para> |
| <synopsis>void (*gem_free_object) (struct drm_gem_object *obj);</synopsis> |
| Drivers are responsible for freeing all GEM object resources, including |
| the resources created by the GEM core. If an mmap offset has been |
| created for the object (in which case |
| <structname>drm_gem_object</structname>::<structfield>map_list</structfield>::<structfield>map</structfield> |
| is not NULL) it must be freed by a call to |
| <function>drm_gem_free_mmap_offset</function>. The shmfs backing store |
| must be released by calling <function>drm_gem_object_release</function> |
| (that function can safely be called if no shmfs backing store has been |
| created). |
| </para> |
| </sect3> |
| <sect3> |
| <title>GEM Objects Naming</title> |
| <para> |
| Communication between userspace and the kernel refers to GEM objects |
| using local handles, global names or, more recently, file descriptors. |
| All of those are 32-bit integer values; the usual Linux kernel limits |
| apply to the file descriptors. |
| </para> |
| <para> |
| GEM handles are local to a DRM file. Applications get a handle to a GEM |
| object through a driver-specific ioctl, and can use that handle to refer |
| to the GEM object in other standard or driver-specific ioctls. Closing a |
| DRM file handle frees all its GEM handles and dereferences the |
| associated GEM objects. |
| </para> |
| <para> |
| To create a handle for a GEM object drivers call |
| <function>drm_gem_handle_create</function>. The function takes a pointer |
| to the DRM file and the GEM object and returns a locally unique handle. |
| When the handle is no longer needed drivers delete it with a call to |
| <function>drm_gem_handle_delete</function>. Finally the GEM object |
| associated with a handle can be retrieved by a call to |
| <function>drm_gem_object_lookup</function>. |
| </para> |
| <para> |
| Handles don't take ownership of GEM objects, they only take a reference |
| to the object that will be dropped when the handle is destroyed. To |
| avoid leaking GEM objects, drivers must make sure they drop the |
| reference(s) they own (such as the initial reference taken at object |
| creation time) as appropriate, without any special consideration for the |
| handle. For example, in the particular case of combined GEM object and |
| handle creation in the implementation of the |
| <methodname>dumb_create</methodname> operation, drivers must drop the |
| initial reference to the GEM object before returning the handle. |
| </para> |
| <para> |
| GEM names are similar in purpose to handles but are not local to DRM |
| files. They can be passed between processes to reference a GEM object |
| globally. Names can't be used directly to refer to objects in the DRM |
| API, applications must convert handles to names and names to handles |
| using the DRM_IOCTL_GEM_FLINK and DRM_IOCTL_GEM_OPEN ioctls |
| respectively. The conversion is handled by the DRM core without any |
| driver-specific support. |
| </para> |
| <para> |
| Similar to global names, GEM file descriptors are also used to share GEM |
| objects across processes. They offer additional security: as file |
| descriptors must be explicitly sent over UNIX domain sockets to be shared |
| between applications, they can't be guessed like the globally unique GEM |
| names. |
| </para> |
| <para> |
| Drivers that support GEM file descriptors, also known as the DRM PRIME |
| API, must set the DRIVER_PRIME bit in the struct |
| <structname>drm_driver</structname> |
| <structfield>driver_features</structfield> field, and implement the |
| <methodname>prime_handle_to_fd</methodname> and |
| <methodname>prime_fd_to_handle</methodname> operations. |
| </para> |
| <para> |
| <synopsis>int (*prime_handle_to_fd)(struct drm_device *dev, |
| struct drm_file *file_priv, uint32_t handle, |
| uint32_t flags, int *prime_fd); |
| int (*prime_fd_to_handle)(struct drm_device *dev, |
| struct drm_file *file_priv, int prime_fd, |
| uint32_t *handle);</synopsis> |
| Those two operations convert a handle to a PRIME file descriptor and |
| vice versa. Drivers must use the kernel dma-buf buffer sharing framework |
| to manage the PRIME file descriptors. |
| </para> |
| <para> |
| While non-GEM drivers must implement the operations themselves, GEM |
| drivers must use the <function>drm_gem_prime_handle_to_fd</function> |
| and <function>drm_gem_prime_fd_to_handle</function> helper functions. |
| Those helpers rely on the driver |
| <methodname>gem_prime_export</methodname> and |
| <methodname>gem_prime_import</methodname> operations to create a dma-buf |
| instance from a GEM object (dma-buf exporter role) and to create a GEM |
| object from a dma-buf instance (dma-buf importer role). |
| </para> |
| <para> |
| <synopsis>struct dma_buf * (*gem_prime_export)(struct drm_device *dev, |
| struct drm_gem_object *obj, |
| int flags); |
| struct drm_gem_object * (*gem_prime_import)(struct drm_device *dev, |
| struct dma_buf *dma_buf);</synopsis> |
| These two operations are mandatory for GEM drivers that support DRM |
| PRIME. |
| </para> |
| <sect4> |
| <title>DRM PRIME Helper Functions Reference</title> |
| !Pdrivers/gpu/drm/drm_prime.c PRIME Helpers |
| </sect4> |
| </sect3> |
| <sect3 id="drm-gem-objects-mapping"> |
| <title>GEM Objects Mapping</title> |
| <para> |
| Because mapping operations are fairly heavyweight GEM favours |
| read/write-like access to buffers, implemented through driver-specific |
| ioctls, over mapping buffers to userspace. However, when random access |
| to the buffer is needed (to perform software rendering for instance), |
| direct access to the object can be more efficient. |
| </para> |
| <para> |
| The mmap system call can't be used directly to map GEM objects, as they |
| don't have their own file handle. Two alternative methods currently |
| co-exist to map GEM objects to userspace. The first method uses a |
| driver-specific ioctl to perform the mapping operation, calling |
| <function>do_mmap</function> under the hood. This is often considered |
| dubious, seems to be discouraged for new GEM-enabled drivers, and will |
| thus not be described here. |
| </para> |
| <para> |
| The second method uses the mmap system call on the DRM file handle. |
| <synopsis>void *mmap(void *addr, size_t length, int prot, int flags, int fd, |
| off_t offset);</synopsis> |
| DRM identifies the GEM object to be mapped by a fake offset passed |
| through the mmap offset argument. Prior to being mapped, a GEM object |
| must thus be associated with a fake offset. To do so, drivers must call |
| <function>drm_gem_create_mmap_offset</function> on the object. The |
| function allocates a fake offset range from a pool and stores the |
| offset divided by PAGE_SIZE in |
| <literal>obj->map_list.hash.key</literal>. Care must be taken not to |
| call <function>drm_gem_create_mmap_offset</function> if a fake offset |
| has already been allocated for the object. This can be tested by |
| <literal>obj->map_list.map</literal> being non-NULL. |
| </para> |
| <para> |
| Once allocated, the fake offset value |
| (<literal>obj->map_list.hash.key << PAGE_SHIFT</literal>) |
| must be passed to the application in a driver-specific way and can then |
| be used as the mmap offset argument. |
| </para> |
| <para> |
| The GEM core provides a helper method <function>drm_gem_mmap</function> |
| to handle object mapping. The method can be set directly as the mmap |
| file operation handler. It will look up the GEM object based on the |
| offset value and set the VMA operations to the |
| <structname>drm_driver</structname> <structfield>gem_vm_ops</structfield> |
| field. Note that <function>drm_gem_mmap</function> doesn't map memory to |
| userspace, but relies on the driver-provided fault handler to map pages |
| individually. |
| </para> |
| <para> |
| To use <function>drm_gem_mmap</function>, drivers must fill the struct |
| <structname>drm_driver</structname> <structfield>gem_vm_ops</structfield> |
| field with a pointer to VM operations. |
| </para> |
| <para> |
| <synopsis>struct vm_operations_struct *gem_vm_ops |
| |
| struct vm_operations_struct { |
| void (*open)(struct vm_area_struct * area); |
| void (*close)(struct vm_area_struct * area); |
| int (*fault)(struct vm_area_struct *vma, struct vm_fault *vmf); |
| };</synopsis> |
| </para> |
| <para> |
| The <methodname>open</methodname> and <methodname>close</methodname> |
| operations must update the GEM object reference count. Drivers can use |
| the <function>drm_gem_vm_open</function> and |
| <function>drm_gem_vm_close</function> helper functions directly as open |
| and close handlers. |
| </para> |
| <para> |
| The fault operation handler is responsible for mapping individual pages |
| to userspace when a page fault occurs. Depending on the memory |
| allocation scheme, drivers can allocate pages at fault time, or can |
| decide to allocate memory for the GEM object at the time the object is |
| created. |
| </para> |
| <para> |
| Drivers that want to map the GEM object upfront instead of handling page |
| faults can implement their own mmap file operation handler. |
| </para> |
| </sect3> |
| <sect3> |
| <title>Memory Coherency</title> |
| <para> |
| When mapped to the device or used in a command buffer, backing pages |
| for an object are flushed to memory and marked write combined so as to |
| be coherent with the GPU. Likewise, if the CPU accesses an object |
| after the GPU has finished rendering to the object, then the object |
| must be made coherent with the CPU's view of memory, usually involving |
| GPU cache flushing of various kinds. This core CPU<->GPU |
| coherency management is provided by a device-specific ioctl, which |
| evaluates an object's current domain and performs any necessary |
| flushing or synchronization to put the object into the desired |
| coherency domain (note that the object may be busy, i.e. an active |
| render target; in that case, setting the domain blocks the client and |
| waits for rendering to complete before performing any necessary |
| flushing operations). |
| </para> |
| </sect3> |
| <sect3> |
| <title>Command Execution</title> |
| <para> |
| Perhaps the most important GEM function for GPU devices is providing a |
| command execution interface to clients. Client programs construct |
| command buffers containing references to previously allocated memory |
| objects, and then submit them to GEM. At that point, GEM takes care to |
| bind all the objects into the GTT, execute the buffer, and provide |
| necessary synchronization between clients accessing the same buffers. |
| This often involves evicting some objects from the GTT and re-binding |
| others (a fairly expensive operation), and providing relocation |
| support which hides fixed GTT offsets from clients. Clients must take |
| care not to submit command buffers that reference more objects than |
| can fit in the GTT; otherwise, GEM will reject them and no rendering |
| will occur. Similarly, if several objects in the buffer require fence |
| registers to be allocated for correct rendering (e.g. 2D blits on |
| pre-965 chips), care must be taken not to require more fence registers |
| than are available to the client. Such resource management should be |
| abstracted from the client in libdrm. |
| </para> |
| </sect3> |
| </sect2> |
| </sect1> |
| |
| <!-- Internals: mode setting --> |
| |
| <sect1 id="drm-mode-setting"> |
| <title>Mode Setting</title> |
| <para> |
| Drivers must initialize the mode setting core by calling |
| <function>drm_mode_config_init</function> on the DRM device. The function |
| initializes the <structname>drm_device</structname> |
| <structfield>mode_config</structfield> field and never fails. Once done, |
| mode configuration must be setup by initializing the following fields. |
| </para> |
| <itemizedlist> |
| <listitem> |
| <synopsis>int min_width, min_height; |
| int max_width, max_height;</synopsis> |
| <para> |
| Minimum and maximum width and height of the frame buffers in pixel |
| units. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>struct drm_mode_config_funcs *funcs;</synopsis> |
| <para>Mode setting functions.</para> |
| </listitem> |
| </itemizedlist> |
| <sect2> |
| <title>Frame Buffer Creation</title> |
| <synopsis>struct drm_framebuffer *(*fb_create)(struct drm_device *dev, |
| struct drm_file *file_priv, |
| struct drm_mode_fb_cmd2 *mode_cmd);</synopsis> |
| <para> |
| Frame buffers are abstract memory objects that provide a source of |
| pixels to scanout to a CRTC. Applications explicitly request the |
| creation of frame buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls and |
| receive an opaque handle that can be passed to the KMS CRTC control, |
| plane configuration and page flip functions. |
| </para> |
| <para> |
| Frame buffers rely on the underneath memory manager for low-level memory |
| operations. When creating a frame buffer applications pass a memory |
| handle (or a list of memory handles for multi-planar formats) through |
| the <parameter>drm_mode_fb_cmd2</parameter> argument. For drivers using |
| GEM as their userspace buffer management interface this would be a GEM |
| handle. Drivers are however free to use their own backing storage object |
| handles, e.g. vmwgfx directly exposes special TTM handles to userspace |
| and so expects TTM handles in the create ioctl and not GEM handles. |
| </para> |
| <para> |
| Drivers must first validate the requested frame buffer parameters passed |
| through the mode_cmd argument. In particular this is where invalid |
| sizes, pixel formats or pitches can be caught. |
| </para> |
| <para> |
| If the parameters are deemed valid, drivers then create, initialize and |
| return an instance of struct <structname>drm_framebuffer</structname>. |
| If desired the instance can be embedded in a larger driver-specific |
| structure. Drivers must fill its <structfield>width</structfield>, |
| <structfield>height</structfield>, <structfield>pitches</structfield>, |
| <structfield>offsets</structfield>, <structfield>depth</structfield>, |
| <structfield>bits_per_pixel</structfield> and |
| <structfield>pixel_format</structfield> fields from the values passed |
| through the <parameter>drm_mode_fb_cmd2</parameter> argument. They |
| should call the <function>drm_helper_mode_fill_fb_struct</function> |
| helper function to do so. |
| </para> |
| |
| <para> |
| The initialization of the new framebuffer instance is finalized with a |
| call to <function>drm_framebuffer_init</function> which takes a pointer |
| to DRM frame buffer operations (struct |
| <structname>drm_framebuffer_funcs</structname>). Note that this function |
| publishes the framebuffer and so from this point on it can be accessed |
| concurrently from other threads. Hence it must be the last step in the |
| driver's framebuffer initialization sequence. Frame buffer operations |
| are |
| <itemizedlist> |
| <listitem> |
| <synopsis>int (*create_handle)(struct drm_framebuffer *fb, |
| struct drm_file *file_priv, unsigned int *handle);</synopsis> |
| <para> |
| Create a handle to the frame buffer underlying memory object. If |
| the frame buffer uses a multi-plane format, the handle will |
| reference the memory object associated with the first plane. |
| </para> |
| <para> |
| Drivers call <function>drm_gem_handle_create</function> to create |
| the handle. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>void (*destroy)(struct drm_framebuffer *framebuffer);</synopsis> |
| <para> |
| Destroy the frame buffer object and frees all associated |
| resources. Drivers must call |
| <function>drm_framebuffer_cleanup</function> to free resources |
| allocated by the DRM core for the frame buffer object, and must |
| make sure to unreference all memory objects associated with the |
| frame buffer. Handles created by the |
| <methodname>create_handle</methodname> operation are released by |
| the DRM core. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>int (*dirty)(struct drm_framebuffer *framebuffer, |
| struct drm_file *file_priv, unsigned flags, unsigned color, |
| struct drm_clip_rect *clips, unsigned num_clips);</synopsis> |
| <para> |
| This optional operation notifies the driver that a region of the |
| frame buffer has changed in response to a DRM_IOCTL_MODE_DIRTYFB |
| ioctl call. |
| </para> |
| </listitem> |
| </itemizedlist> |
| </para> |
| <para> |
| The lifetime of a drm framebuffer is controlled with a reference count, |
| drivers can grab additional references with |
| <function>drm_framebuffer_reference</function> </para> and drop them |
| again with <function>drm_framebuffer_unreference</function>. For |
| driver-private framebuffers for which the last reference is never |
| dropped (e.g. for the fbdev framebuffer when the struct |
| <structname>drm_framebuffer</structname> is embedded into the fbdev |
| helper struct) drivers can manually clean up a framebuffer at module |
| unload time with |
| <function>drm_framebuffer_unregister_private</function>. |
| </sect2> |
| <sect2> |
| <title>Dumb Buffer Objects</title> |
| <para> |
| The KMS API doesn't standardize backing storage object creation and |
| leaves it to driver-specific ioctls. Furthermore actually creating a |
| buffer object even for GEM-based drivers is done through a |
| driver-specific ioctl - GEM only has a common userspace interface for |
| sharing and destroying objects. While not an issue for full-fledged |
| graphics stacks that include device-specific userspace components (in |
| libdrm for instance), this limit makes DRM-based early boot graphics |
| unnecessarily complex. |
| </para> |
| <para> |
| Dumb objects partly alleviate the problem by providing a standard |
| API to create dumb buffers suitable for scanout, which can then be used |
| to create KMS frame buffers. |
| </para> |
| <para> |
| To support dumb objects drivers must implement the |
| <methodname>dumb_create</methodname>, |
| <methodname>dumb_destroy</methodname> and |
| <methodname>dumb_map_offset</methodname> operations. |
| </para> |
| <itemizedlist> |
| <listitem> |
| <synopsis>int (*dumb_create)(struct drm_file *file_priv, struct drm_device *dev, |
| struct drm_mode_create_dumb *args);</synopsis> |
| <para> |
| The <methodname>dumb_create</methodname> operation creates a driver |
| object (GEM or TTM handle) suitable for scanout based on the |
| width, height and depth from the struct |
| <structname>drm_mode_create_dumb</structname> argument. It fills the |
| argument's <structfield>handle</structfield>, |
| <structfield>pitch</structfield> and <structfield>size</structfield> |
| fields with a handle for the newly created object and its line |
| pitch and size in bytes. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>int (*dumb_destroy)(struct drm_file *file_priv, struct drm_device *dev, |
| uint32_t handle);</synopsis> |
| <para> |
| The <methodname>dumb_destroy</methodname> operation destroys a dumb |
| object created by <methodname>dumb_create</methodname>. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>int (*dumb_map_offset)(struct drm_file *file_priv, struct drm_device *dev, |
| uint32_t handle, uint64_t *offset);</synopsis> |
| <para> |
| The <methodname>dumb_map_offset</methodname> operation associates an |
| mmap fake offset with the object given by the handle and returns |
| it. Drivers must use the |
| <function>drm_gem_create_mmap_offset</function> function to |
| associate the fake offset as described in |
| <xref linkend="drm-gem-objects-mapping"/>. |
| </para> |
| </listitem> |
| </itemizedlist> |
| <para> |
| Note that dumb objects may not be used for gpu acceleration, as has been |
| attempted on some ARM embedded platforms. Such drivers really must have |
| a hardware-specific ioctl to allocate suitable buffer objects. |
| </para> |
| </sect2> |
| <sect2> |
| <title>Output Polling</title> |
| <synopsis>void (*output_poll_changed)(struct drm_device *dev);</synopsis> |
| <para> |
| This operation notifies the driver that the status of one or more |
| connectors has changed. Drivers that use the fb helper can just call the |
| <function>drm_fb_helper_hotplug_event</function> function to handle this |
| operation. |
| </para> |
| </sect2> |
| <sect2> |
| <title>Locking</title> |
| <para> |
| Beside some lookup structures with their own locking (which is hidden |
| behind the interface functions) most of the modeset state is protected |
| by the <code>dev-<mode_config.lock</code> mutex and additionally |
| per-crtc locks to allow cursor updates, pageflips and similar operations |
| to occur concurrently with background tasks like output detection. |
| Operations which cross domains like a full modeset always grab all |
| locks. Drivers there need to protect resources shared between crtcs with |
| additional locking. They also need to be careful to always grab the |
| relevant crtc locks if a modset functions touches crtc state, e.g. for |
| load detection (which does only grab the <code>mode_config.lock</code> |
| to allow concurrent screen updates on live crtcs). |
| </para> |
| </sect2> |
| </sect1> |
| |
| <!-- Internals: kms initialization and cleanup --> |
| |
| <sect1 id="drm-kms-init"> |
| <title>KMS Initialization and Cleanup</title> |
| <para> |
| A KMS device is abstracted and exposed as a set of planes, CRTCs, encoders |
| and connectors. KMS drivers must thus create and initialize all those |
| objects at load time after initializing mode setting. |
| </para> |
| <sect2> |
| <title>CRTCs (struct <structname>drm_crtc</structname>)</title> |
| <para> |
| A CRTC is an abstraction representing a part of the chip that contains a |
| pointer to a scanout buffer. Therefore, the number of CRTCs available |
| determines how many independent scanout buffers can be active at any |
| given time. The CRTC structure contains several fields to support this: |
| a pointer to some video memory (abstracted as a frame buffer object), a |
| display mode, and an (x, y) offset into the video memory to support |
| panning or configurations where one piece of video memory spans multiple |
| CRTCs. |
| </para> |
| <sect3> |
| <title>CRTC Initialization</title> |
| <para> |
| A KMS device must create and register at least one struct |
| <structname>drm_crtc</structname> instance. The instance is allocated |
| and zeroed by the driver, possibly as part of a larger structure, and |
| registered with a call to <function>drm_crtc_init</function> with a |
| pointer to CRTC functions. |
| </para> |
| </sect3> |
| <sect3> |
| <title>CRTC Operations</title> |
| <sect4> |
| <title>Set Configuration</title> |
| <synopsis>int (*set_config)(struct drm_mode_set *set);</synopsis> |
| <para> |
| Apply a new CRTC configuration to the device. The configuration |
| specifies a CRTC, a frame buffer to scan out from, a (x,y) position in |
| the frame buffer, a display mode and an array of connectors to drive |
| with the CRTC if possible. |
| </para> |
| <para> |
| If the frame buffer specified in the configuration is NULL, the driver |
| must detach all encoders connected to the CRTC and all connectors |
| attached to those encoders and disable them. |
| </para> |
| <para> |
| This operation is called with the mode config lock held. |
| </para> |
| <note><para> |
| FIXME: How should set_config interact with DPMS? If the CRTC is |
| suspended, should it be resumed? |
| </para></note> |
| </sect4> |
| <sect4> |
| <title>Page Flipping</title> |
| <synopsis>int (*page_flip)(struct drm_crtc *crtc, struct drm_framebuffer *fb, |
| struct drm_pending_vblank_event *event);</synopsis> |
| <para> |
| Schedule a page flip to the given frame buffer for the CRTC. This |
| operation is called with the mode config mutex held. |
| </para> |
| <para> |
| Page flipping is a synchronization mechanism that replaces the frame |
| buffer being scanned out by the CRTC with a new frame buffer during |
| vertical blanking, avoiding tearing. When an application requests a page |
| flip the DRM core verifies that the new frame buffer is large enough to |
| be scanned out by the CRTC in the currently configured mode and then |
| calls the CRTC <methodname>page_flip</methodname> operation with a |
| pointer to the new frame buffer. |
| </para> |
| <para> |
| The <methodname>page_flip</methodname> operation schedules a page flip. |
| Once any pending rendering targeting the new frame buffer has |
| completed, the CRTC will be reprogrammed to display that frame buffer |
| after the next vertical refresh. The operation must return immediately |
| without waiting for rendering or page flip to complete and must block |
| any new rendering to the frame buffer until the page flip completes. |
| </para> |
| <para> |
| If a page flip can be successfully scheduled the driver must set the |
| <code>drm_crtc-<fb</code> field to the new framebuffer pointed to |
| by <code>fb</code>. This is important so that the reference counting |
| on framebuffers stays balanced. |
| </para> |
| <para> |
| If a page flip is already pending, the |
| <methodname>page_flip</methodname> operation must return |
| -<errorname>EBUSY</errorname>. |
| </para> |
| <para> |
| To synchronize page flip to vertical blanking the driver will likely |
| need to enable vertical blanking interrupts. It should call |
| <function>drm_vblank_get</function> for that purpose, and call |
| <function>drm_vblank_put</function> after the page flip completes. |
| </para> |
| <para> |
| If the application has requested to be notified when page flip completes |
| the <methodname>page_flip</methodname> operation will be called with a |
| non-NULL <parameter>event</parameter> argument pointing to a |
| <structname>drm_pending_vblank_event</structname> instance. Upon page |
| flip completion the driver must call <methodname>drm_send_vblank_event</methodname> |
| to fill in the event and send to wake up any waiting processes. |
| This can be performed with |
| <programlisting><![CDATA[ |
| spin_lock_irqsave(&dev->event_lock, flags); |
| ... |
| drm_send_vblank_event(dev, pipe, event); |
| spin_unlock_irqrestore(&dev->event_lock, flags); |
| ]]></programlisting> |
| </para> |
| <note><para> |
| FIXME: Could drivers that don't need to wait for rendering to complete |
| just add the event to <literal>dev->vblank_event_list</literal> and |
| let the DRM core handle everything, as for "normal" vertical blanking |
| events? |
| </para></note> |
| <para> |
| While waiting for the page flip to complete, the |
| <literal>event->base.link</literal> list head can be used freely by |
| the driver to store the pending event in a driver-specific list. |
| </para> |
| <para> |
| If the file handle is closed before the event is signaled, drivers must |
| take care to destroy the event in their |
| <methodname>preclose</methodname> operation (and, if needed, call |
| <function>drm_vblank_put</function>). |
| </para> |
| </sect4> |
| <sect4> |
| <title>Miscellaneous</title> |
| <itemizedlist> |
| <listitem> |
| <synopsis>void (*set_property)(struct drm_crtc *crtc, |
| struct drm_property *property, uint64_t value);</synopsis> |
| <para> |
| Set the value of the given CRTC property to |
| <parameter>value</parameter>. See <xref linkend="drm-kms-properties"/> |
| for more information about properties. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>void (*gamma_set)(struct drm_crtc *crtc, u16 *r, u16 *g, u16 *b, |
| uint32_t start, uint32_t size);</synopsis> |
| <para> |
| Apply a gamma table to the device. The operation is optional. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>void (*destroy)(struct drm_crtc *crtc);</synopsis> |
| <para> |
| Destroy the CRTC when not needed anymore. See |
| <xref linkend="drm-kms-init"/>. |
| </para> |
| </listitem> |
| </itemizedlist> |
| </sect4> |
| </sect3> |
| </sect2> |
| <sect2> |
| <title>Planes (struct <structname>drm_plane</structname>)</title> |
| <para> |
| A plane represents an image source that can be blended with or overlayed |
| on top of a CRTC during the scanout process. Planes are associated with |
| a frame buffer to crop a portion of the image memory (source) and |
| optionally scale it to a destination size. The result is then blended |
| with or overlayed on top of a CRTC. |
| </para> |
| <sect3> |
| <title>Plane Initialization</title> |
| <para> |
| Planes are optional. To create a plane, a KMS drivers allocates and |
| zeroes an instances of struct <structname>drm_plane</structname> |
| (possibly as part of a larger structure) and registers it with a call |
| to <function>drm_plane_init</function>. The function takes a bitmask |
| of the CRTCs that can be associated with the plane, a pointer to the |
| plane functions and a list of format supported formats. |
| </para> |
| </sect3> |
| <sect3> |
| <title>Plane Operations</title> |
| <itemizedlist> |
| <listitem> |
| <synopsis>int (*update_plane)(struct drm_plane *plane, struct drm_crtc *crtc, |
| struct drm_framebuffer *fb, int crtc_x, int crtc_y, |
| unsigned int crtc_w, unsigned int crtc_h, |
| uint32_t src_x, uint32_t src_y, |
| uint32_t src_w, uint32_t src_h);</synopsis> |
| <para> |
| Enable and configure the plane to use the given CRTC and frame buffer. |
| </para> |
| <para> |
| The source rectangle in frame buffer memory coordinates is given by |
| the <parameter>src_x</parameter>, <parameter>src_y</parameter>, |
| <parameter>src_w</parameter> and <parameter>src_h</parameter> |
| parameters (as 16.16 fixed point values). Devices that don't support |
| subpixel plane coordinates can ignore the fractional part. |
| </para> |
| <para> |
| The destination rectangle in CRTC coordinates is given by the |
| <parameter>crtc_x</parameter>, <parameter>crtc_y</parameter>, |
| <parameter>crtc_w</parameter> and <parameter>crtc_h</parameter> |
| parameters (as integer values). Devices scale the source rectangle to |
| the destination rectangle. If scaling is not supported, and the source |
| rectangle size doesn't match the destination rectangle size, the |
| driver must return a -<errorname>EINVAL</errorname> error. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>int (*disable_plane)(struct drm_plane *plane);</synopsis> |
| <para> |
| Disable the plane. The DRM core calls this method in response to a |
| DRM_IOCTL_MODE_SETPLANE ioctl call with the frame buffer ID set to 0. |
| Disabled planes must not be processed by the CRTC. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>void (*destroy)(struct drm_plane *plane);</synopsis> |
| <para> |
| Destroy the plane when not needed anymore. See |
| <xref linkend="drm-kms-init"/>. |
| </para> |
| </listitem> |
| </itemizedlist> |
| </sect3> |
| </sect2> |
| <sect2> |
| <title>Encoders (struct <structname>drm_encoder</structname>)</title> |
| <para> |
| An encoder takes pixel data from a CRTC and converts it to a format |
| suitable for any attached connectors. On some devices, it may be |
| possible to have a CRTC send data to more than one encoder. In that |
| case, both encoders would receive data from the same scanout buffer, |
| resulting in a "cloned" display configuration across the connectors |
| attached to each encoder. |
| </para> |
| <sect3> |
| <title>Encoder Initialization</title> |
| <para> |
| As for CRTCs, a KMS driver must create, initialize and register at |
| least one struct <structname>drm_encoder</structname> instance. The |
| instance is allocated and zeroed by the driver, possibly as part of a |
| larger structure. |
| </para> |
| <para> |
| Drivers must initialize the struct <structname>drm_encoder</structname> |
| <structfield>possible_crtcs</structfield> and |
| <structfield>possible_clones</structfield> fields before registering the |
| encoder. Both fields are bitmasks of respectively the CRTCs that the |
| encoder can be connected to, and sibling encoders candidate for cloning. |
| </para> |
| <para> |
| After being initialized, the encoder must be registered with a call to |
| <function>drm_encoder_init</function>. The function takes a pointer to |
| the encoder functions and an encoder type. Supported types are |
| <itemizedlist> |
| <listitem> |
| DRM_MODE_ENCODER_DAC for VGA and analog on DVI-I/DVI-A |
| </listitem> |
| <listitem> |
| DRM_MODE_ENCODER_TMDS for DVI, HDMI and (embedded) DisplayPort |
| </listitem> |
| <listitem> |
| DRM_MODE_ENCODER_LVDS for display panels |
| </listitem> |
| <listitem> |
| DRM_MODE_ENCODER_TVDAC for TV output (Composite, S-Video, Component, |
| SCART) |
| </listitem> |
| <listitem> |
| DRM_MODE_ENCODER_VIRTUAL for virtual machine displays |
| </listitem> |
| </itemizedlist> |
| </para> |
| <para> |
| Encoders must be attached to a CRTC to be used. DRM drivers leave |
| encoders unattached at initialization time. Applications (or the fbdev |
| compatibility layer when implemented) are responsible for attaching the |
| encoders they want to use to a CRTC. |
| </para> |
| </sect3> |
| <sect3> |
| <title>Encoder Operations</title> |
| <itemizedlist> |
| <listitem> |
| <synopsis>void (*destroy)(struct drm_encoder *encoder);</synopsis> |
| <para> |
| Called to destroy the encoder when not needed anymore. See |
| <xref linkend="drm-kms-init"/>. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>void (*set_property)(struct drm_plane *plane, |
| struct drm_property *property, uint64_t value);</synopsis> |
| <para> |
| Set the value of the given plane property to |
| <parameter>value</parameter>. See <xref linkend="drm-kms-properties"/> |
| for more information about properties. |
| </para> |
| </listitem> |
| </itemizedlist> |
| </sect3> |
| </sect2> |
| <sect2> |
| <title>Connectors (struct <structname>drm_connector</structname>)</title> |
| <para> |
| A connector is the final destination for pixel data on a device, and |
| usually connects directly to an external display device like a monitor |
| or laptop panel. A connector can only be attached to one encoder at a |
| time. The connector is also the structure where information about the |
| attached display is kept, so it contains fields for display data, EDID |
| data, DPMS & connection status, and information about modes |
| supported on the attached displays. |
| </para> |
| <sect3> |
| <title>Connector Initialization</title> |
| <para> |
| Finally a KMS driver must create, initialize, register and attach at |
| least one struct <structname>drm_connector</structname> instance. The |
| instance is created as other KMS objects and initialized by setting the |
| following fields. |
| </para> |
| <variablelist> |
| <varlistentry> |
| <term><structfield>interlace_allowed</structfield></term> |
| <listitem><para> |
| Whether the connector can handle interlaced modes. |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term><structfield>doublescan_allowed</structfield></term> |
| <listitem><para> |
| Whether the connector can handle doublescan. |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term><structfield>display_info |
| </structfield></term> |
| <listitem><para> |
| Display information is filled from EDID information when a display |
| is detected. For non hot-pluggable displays such as flat panels in |
| embedded systems, the driver should initialize the |
| <structfield>display_info</structfield>.<structfield>width_mm</structfield> |
| and |
| <structfield>display_info</structfield>.<structfield>height_mm</structfield> |
| fields with the physical size of the display. |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term id="drm-kms-connector-polled"><structfield>polled</structfield></term> |
| <listitem><para> |
| Connector polling mode, a combination of |
| <variablelist> |
| <varlistentry> |
| <term>DRM_CONNECTOR_POLL_HPD</term> |
| <listitem><para> |
| The connector generates hotplug events and doesn't need to be |
| periodically polled. The CONNECT and DISCONNECT flags must not |
| be set together with the HPD flag. |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_CONNECTOR_POLL_CONNECT</term> |
| <listitem><para> |
| Periodically poll the connector for connection. |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_CONNECTOR_POLL_DISCONNECT</term> |
| <listitem><para> |
| Periodically poll the connector for disconnection. |
| </para></listitem> |
| </varlistentry> |
| </variablelist> |
| Set to 0 for connectors that don't support connection status |
| discovery. |
| </para></listitem> |
| </varlistentry> |
| </variablelist> |
| <para> |
| The connector is then registered with a call to |
| <function>drm_connector_init</function> with a pointer to the connector |
| functions and a connector type, and exposed through sysfs with a call to |
| <function>drm_sysfs_connector_add</function>. |
| </para> |
| <para> |
| Supported connector types are |
| <itemizedlist> |
| <listitem>DRM_MODE_CONNECTOR_VGA</listitem> |
| <listitem>DRM_MODE_CONNECTOR_DVII</listitem> |
| <listitem>DRM_MODE_CONNECTOR_DVID</listitem> |
| <listitem>DRM_MODE_CONNECTOR_DVIA</listitem> |
| <listitem>DRM_MODE_CONNECTOR_Composite</listitem> |
| <listitem>DRM_MODE_CONNECTOR_SVIDEO</listitem> |
| <listitem>DRM_MODE_CONNECTOR_LVDS</listitem> |
| <listitem>DRM_MODE_CONNECTOR_Component</listitem> |
| <listitem>DRM_MODE_CONNECTOR_9PinDIN</listitem> |
| <listitem>DRM_MODE_CONNECTOR_DisplayPort</listitem> |
| <listitem>DRM_MODE_CONNECTOR_HDMIA</listitem> |
| <listitem>DRM_MODE_CONNECTOR_HDMIB</listitem> |
| <listitem>DRM_MODE_CONNECTOR_TV</listitem> |
| <listitem>DRM_MODE_CONNECTOR_eDP</listitem> |
| <listitem>DRM_MODE_CONNECTOR_VIRTUAL</listitem> |
| </itemizedlist> |
| </para> |
| <para> |
| Connectors must be attached to an encoder to be used. For devices that |
| map connectors to encoders 1:1, the connector should be attached at |
| initialization time with a call to |
| <function>drm_mode_connector_attach_encoder</function>. The driver must |
| also set the <structname>drm_connector</structname> |
| <structfield>encoder</structfield> field to point to the attached |
| encoder. |
| </para> |
| <para> |
| Finally, drivers must initialize the connectors state change detection |
| with a call to <function>drm_kms_helper_poll_init</function>. If at |
| least one connector is pollable but can't generate hotplug interrupts |
| (indicated by the DRM_CONNECTOR_POLL_CONNECT and |
| DRM_CONNECTOR_POLL_DISCONNECT connector flags), a delayed work will |
| automatically be queued to periodically poll for changes. Connectors |
| that can generate hotplug interrupts must be marked with the |
| DRM_CONNECTOR_POLL_HPD flag instead, and their interrupt handler must |
| call <function>drm_helper_hpd_irq_event</function>. The function will |
| queue a delayed work to check the state of all connectors, but no |
| periodic polling will be done. |
| </para> |
| </sect3> |
| <sect3> |
| <title>Connector Operations</title> |
| <note><para> |
| Unless otherwise state, all operations are mandatory. |
| </para></note> |
| <sect4> |
| <title>DPMS</title> |
| <synopsis>void (*dpms)(struct drm_connector *connector, int mode);</synopsis> |
| <para> |
| The DPMS operation sets the power state of a connector. The mode |
| argument is one of |
| <itemizedlist> |
| <listitem><para>DRM_MODE_DPMS_ON</para></listitem> |
| <listitem><para>DRM_MODE_DPMS_STANDBY</para></listitem> |
| <listitem><para>DRM_MODE_DPMS_SUSPEND</para></listitem> |
| <listitem><para>DRM_MODE_DPMS_OFF</para></listitem> |
| </itemizedlist> |
| </para> |
| <para> |
| In all but DPMS_ON mode the encoder to which the connector is attached |
| should put the display in low-power mode by driving its signals |
| appropriately. If more than one connector is attached to the encoder |
| care should be taken not to change the power state of other displays as |
| a side effect. Low-power mode should be propagated to the encoders and |
| CRTCs when all related connectors are put in low-power mode. |
| </para> |
| </sect4> |
| <sect4> |
| <title>Modes</title> |
| <synopsis>int (*fill_modes)(struct drm_connector *connector, uint32_t max_width, |
| uint32_t max_height);</synopsis> |
| <para> |
| Fill the mode list with all supported modes for the connector. If the |
| <parameter>max_width</parameter> and <parameter>max_height</parameter> |
| arguments are non-zero, the implementation must ignore all modes wider |
| than <parameter>max_width</parameter> or higher than |
| <parameter>max_height</parameter>. |
| </para> |
| <para> |
| The connector must also fill in this operation its |
| <structfield>display_info</structfield> |
| <structfield>width_mm</structfield> and |
| <structfield>height_mm</structfield> fields with the connected display |
| physical size in millimeters. The fields should be set to 0 if the value |
| isn't known or is not applicable (for instance for projector devices). |
| </para> |
| </sect4> |
| <sect4> |
| <title>Connection Status</title> |
| <para> |
| The connection status is updated through polling or hotplug events when |
| supported (see <xref linkend="drm-kms-connector-polled"/>). The status |
| value is reported to userspace through ioctls and must not be used |
| inside the driver, as it only gets initialized by a call to |
| <function>drm_mode_getconnector</function> from userspace. |
| </para> |
| <synopsis>enum drm_connector_status (*detect)(struct drm_connector *connector, |
| bool force);</synopsis> |
| <para> |
| Check to see if anything is attached to the connector. The |
| <parameter>force</parameter> parameter is set to false whilst polling or |
| to true when checking the connector due to user request. |
| <parameter>force</parameter> can be used by the driver to avoid |
| expensive, destructive operations during automated probing. |
| </para> |
| <para> |
| Return connector_status_connected if something is connected to the |
| connector, connector_status_disconnected if nothing is connected and |
| connector_status_unknown if the connection state isn't known. |
| </para> |
| <para> |
| Drivers should only return connector_status_connected if the connection |
| status has really been probed as connected. Connectors that can't detect |
| the connection status, or failed connection status probes, should return |
| connector_status_unknown. |
| </para> |
| </sect4> |
| <sect4> |
| <title>Miscellaneous</title> |
| <itemizedlist> |
| <listitem> |
| <synopsis>void (*set_property)(struct drm_connector *connector, |
| struct drm_property *property, uint64_t value);</synopsis> |
| <para> |
| Set the value of the given connector property to |
| <parameter>value</parameter>. See <xref linkend="drm-kms-properties"/> |
| for more information about properties. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>void (*destroy)(struct drm_connector *connector);</synopsis> |
| <para> |
| Destroy the connector when not needed anymore. See |
| <xref linkend="drm-kms-init"/>. |
| </para> |
| </listitem> |
| </itemizedlist> |
| </sect4> |
| </sect3> |
| </sect2> |
| <sect2> |
| <title>Cleanup</title> |
| <para> |
| The DRM core manages its objects' lifetime. When an object is not needed |
| anymore the core calls its destroy function, which must clean up and |
| free every resource allocated for the object. Every |
| <function>drm_*_init</function> call must be matched with a |
| corresponding <function>drm_*_cleanup</function> call to cleanup CRTCs |
| (<function>drm_crtc_cleanup</function>), planes |
| (<function>drm_plane_cleanup</function>), encoders |
| (<function>drm_encoder_cleanup</function>) and connectors |
| (<function>drm_connector_cleanup</function>). Furthermore, connectors |
| that have been added to sysfs must be removed by a call to |
| <function>drm_sysfs_connector_remove</function> before calling |
| <function>drm_connector_cleanup</function>. |
| </para> |
| <para> |
| Connectors state change detection must be cleanup up with a call to |
| <function>drm_kms_helper_poll_fini</function>. |
| </para> |
| </sect2> |
| <sect2> |
| <title>Output discovery and initialization example</title> |
| <programlisting><![CDATA[ |
| void intel_crt_init(struct drm_device *dev) |
| { |
| struct drm_connector *connector; |
| struct intel_output *intel_output; |
| |
| intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL); |
| if (!intel_output) |
| return; |
| |
| connector = &intel_output->base; |
| drm_connector_init(dev, &intel_output->base, |
| &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA); |
| |
| drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs, |
| DRM_MODE_ENCODER_DAC); |
| |
| drm_mode_connector_attach_encoder(&intel_output->base, |
| &intel_output->enc); |
| |
| /* Set up the DDC bus. */ |
| intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A"); |
| if (!intel_output->ddc_bus) { |
| dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration " |
| "failed.\n"); |
| return; |
| } |
| |
| intel_output->type = INTEL_OUTPUT_ANALOG; |
| connector->interlace_allowed = 0; |
| connector->doublescan_allowed = 0; |
| |
| drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs); |
| drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs); |
| |
| drm_sysfs_connector_add(connector); |
| }]]></programlisting> |
| <para> |
| In the example above (taken from the i915 driver), a CRTC, connector and |
| encoder combination is created. A device-specific i2c bus is also |
| created for fetching EDID data and performing monitor detection. Once |
| the process is complete, the new connector is registered with sysfs to |
| make its properties available to applications. |
| </para> |
| </sect2> |
| <sect2> |
| <title>KMS API Functions</title> |
| !Edrivers/gpu/drm/drm_crtc.c |
| </sect2> |
| </sect1> |
| |
| <!-- Internals: kms helper functions --> |
| |
| <sect1> |
| <title>Mode Setting Helper Functions</title> |
| <para> |
| The CRTC, encoder and connector functions provided by the drivers |
| implement the DRM API. They're called by the DRM core and ioctl handlers |
| to handle device state changes and configuration request. As implementing |
| those functions often requires logic not specific to drivers, mid-layer |
| helper functions are available to avoid duplicating boilerplate code. |
| </para> |
| <para> |
| The DRM core contains one mid-layer implementation. The mid-layer provides |
| implementations of several CRTC, encoder and connector functions (called |
| from the top of the mid-layer) that pre-process requests and call |
| lower-level functions provided by the driver (at the bottom of the |
| mid-layer). For instance, the |
| <function>drm_crtc_helper_set_config</function> function can be used to |
| fill the struct <structname>drm_crtc_funcs</structname> |
| <structfield>set_config</structfield> field. When called, it will split |
| the <methodname>set_config</methodname> operation in smaller, simpler |
| operations and call the driver to handle them. |
| </para> |
| <para> |
| To use the mid-layer, drivers call <function>drm_crtc_helper_add</function>, |
| <function>drm_encoder_helper_add</function> and |
| <function>drm_connector_helper_add</function> functions to install their |
| mid-layer bottom operations handlers, and fill the |
| <structname>drm_crtc_funcs</structname>, |
| <structname>drm_encoder_funcs</structname> and |
| <structname>drm_connector_funcs</structname> structures with pointers to |
| the mid-layer top API functions. Installing the mid-layer bottom operation |
| handlers is best done right after registering the corresponding KMS object. |
| </para> |
| <para> |
| The mid-layer is not split between CRTC, encoder and connector operations. |
| To use it, a driver must provide bottom functions for all of the three KMS |
| entities. |
| </para> |
| <sect2> |
| <title>Helper Functions</title> |
| <itemizedlist> |
| <listitem> |
| <synopsis>int drm_crtc_helper_set_config(struct drm_mode_set *set);</synopsis> |
| <para> |
| The <function>drm_crtc_helper_set_config</function> helper function |
| is a CRTC <methodname>set_config</methodname> implementation. It |
| first tries to locate the best encoder for each connector by calling |
| the connector <methodname>best_encoder</methodname> helper |
| operation. |
| </para> |
| <para> |
| After locating the appropriate encoders, the helper function will |
| call the <methodname>mode_fixup</methodname> encoder and CRTC helper |
| operations to adjust the requested mode, or reject it completely in |
| which case an error will be returned to the application. If the new |
| configuration after mode adjustment is identical to the current |
| configuration the helper function will return without performing any |
| other operation. |
| </para> |
| <para> |
| If the adjusted mode is identical to the current mode but changes to |
| the frame buffer need to be applied, the |
| <function>drm_crtc_helper_set_config</function> function will call |
| the CRTC <methodname>mode_set_base</methodname> helper operation. If |
| the adjusted mode differs from the current mode, or if the |
| <methodname>mode_set_base</methodname> helper operation is not |
| provided, the helper function performs a full mode set sequence by |
| calling the <methodname>prepare</methodname>, |
| <methodname>mode_set</methodname> and |
| <methodname>commit</methodname> CRTC and encoder helper operations, |
| in that order. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>void drm_helper_connector_dpms(struct drm_connector *connector, int mode);</synopsis> |
| <para> |
| The <function>drm_helper_connector_dpms</function> helper function |
| is a connector <methodname>dpms</methodname> implementation that |
| tracks power state of connectors. To use the function, drivers must |
| provide <methodname>dpms</methodname> helper operations for CRTCs |
| and encoders to apply the DPMS state to the device. |
| </para> |
| <para> |
| The mid-layer doesn't track the power state of CRTCs and encoders. |
| The <methodname>dpms</methodname> helper operations can thus be |
| called with a mode identical to the currently active mode. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>int drm_helper_probe_single_connector_modes(struct drm_connector *connector, |
| uint32_t maxX, uint32_t maxY);</synopsis> |
| <para> |
| The <function>drm_helper_probe_single_connector_modes</function> helper |
| function is a connector <methodname>fill_modes</methodname> |
| implementation that updates the connection status for the connector |
| and then retrieves a list of modes by calling the connector |
| <methodname>get_modes</methodname> helper operation. |
| </para> |
| <para> |
| The function filters out modes larger than |
| <parameter>max_width</parameter> and <parameter>max_height</parameter> |
| if specified. It then calls the connector |
| <methodname>mode_valid</methodname> helper operation for each mode in |
| the probed list to check whether the mode is valid for the connector. |
| </para> |
| </listitem> |
| </itemizedlist> |
| </sect2> |
| <sect2> |
| <title>CRTC Helper Operations</title> |
| <itemizedlist> |
| <listitem id="drm-helper-crtc-mode-fixup"> |
| <synopsis>bool (*mode_fixup)(struct drm_crtc *crtc, |
| const struct drm_display_mode *mode, |
| struct drm_display_mode *adjusted_mode);</synopsis> |
| <para> |
| Let CRTCs adjust the requested mode or reject it completely. This |
| operation returns true if the mode is accepted (possibly after being |
| adjusted) or false if it is rejected. |
| </para> |
| <para> |
| The <methodname>mode_fixup</methodname> operation should reject the |
| mode if it can't reasonably use it. The definition of "reasonable" |
| is currently fuzzy in this context. One possible behaviour would be |
| to set the adjusted mode to the panel timings when a fixed-mode |
| panel is used with hardware capable of scaling. Another behaviour |
| would be to accept any input mode and adjust it to the closest mode |
| supported by the hardware (FIXME: This needs to be clarified). |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>int (*mode_set_base)(struct drm_crtc *crtc, int x, int y, |
| struct drm_framebuffer *old_fb)</synopsis> |
| <para> |
| Move the CRTC on the current frame buffer (stored in |
| <literal>crtc->fb</literal>) to position (x,y). Any of the frame |
| buffer, x position or y position may have been modified. |
| </para> |
| <para> |
| This helper operation is optional. If not provided, the |
| <function>drm_crtc_helper_set_config</function> function will fall |
| back to the <methodname>mode_set</methodname> helper operation. |
| </para> |
| <note><para> |
| FIXME: Why are x and y passed as arguments, as they can be accessed |
| through <literal>crtc->x</literal> and |
| <literal>crtc->y</literal>? |
| </para></note> |
| </listitem> |
| <listitem> |
| <synopsis>void (*prepare)(struct drm_crtc *crtc);</synopsis> |
| <para> |
| Prepare the CRTC for mode setting. This operation is called after |
| validating the requested mode. Drivers use it to perform |
| device-specific operations required before setting the new mode. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>int (*mode_set)(struct drm_crtc *crtc, struct drm_display_mode *mode, |
| struct drm_display_mode *adjusted_mode, int x, int y, |
| struct drm_framebuffer *old_fb);</synopsis> |
| <para> |
| Set a new mode, position and frame buffer. Depending on the device |
| requirements, the mode can be stored internally by the driver and |
| applied in the <methodname>commit</methodname> operation, or |
| programmed to the hardware immediately. |
| </para> |
| <para> |
| The <methodname>mode_set</methodname> operation returns 0 on success |
| or a negative error code if an error occurs. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>void (*commit)(struct drm_crtc *crtc);</synopsis> |
| <para> |
| Commit a mode. This operation is called after setting the new mode. |
| Upon return the device must use the new mode and be fully |
| operational. |
| </para> |
| </listitem> |
| </itemizedlist> |
| </sect2> |
| <sect2> |
| <title>Encoder Helper Operations</title> |
| <itemizedlist> |
| <listitem> |
| <synopsis>bool (*mode_fixup)(struct drm_encoder *encoder, |
| const struct drm_display_mode *mode, |
| struct drm_display_mode *adjusted_mode);</synopsis> |
| <para> |
| Let encoders adjust the requested mode or reject it completely. This |
| operation returns true if the mode is accepted (possibly after being |
| adjusted) or false if it is rejected. See the |
| <link linkend="drm-helper-crtc-mode-fixup">mode_fixup CRTC helper |
| operation</link> for an explanation of the allowed adjustments. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>void (*prepare)(struct drm_encoder *encoder);</synopsis> |
| <para> |
| Prepare the encoder for mode setting. This operation is called after |
| validating the requested mode. Drivers use it to perform |
| device-specific operations required before setting the new mode. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>void (*mode_set)(struct drm_encoder *encoder, |
| struct drm_display_mode *mode, |
| struct drm_display_mode *adjusted_mode);</synopsis> |
| <para> |
| Set a new mode. Depending on the device requirements, the mode can |
| be stored internally by the driver and applied in the |
| <methodname>commit</methodname> operation, or programmed to the |
| hardware immediately. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>void (*commit)(struct drm_encoder *encoder);</synopsis> |
| <para> |
| Commit a mode. This operation is called after setting the new mode. |
| Upon return the device must use the new mode and be fully |
| operational. |
| </para> |
| </listitem> |
| </itemizedlist> |
| </sect2> |
| <sect2> |
| <title>Connector Helper Operations</title> |
| <itemizedlist> |
| <listitem> |
| <synopsis>struct drm_encoder *(*best_encoder)(struct drm_connector *connector);</synopsis> |
| <para> |
| Return a pointer to the best encoder for the connecter. Device that |
| map connectors to encoders 1:1 simply return the pointer to the |
| associated encoder. This operation is mandatory. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>int (*get_modes)(struct drm_connector *connector);</synopsis> |
| <para> |
| Fill the connector's <structfield>probed_modes</structfield> list |
| by parsing EDID data with <function>drm_add_edid_modes</function> or |
| calling <function>drm_mode_probed_add</function> directly for every |
| supported mode and return the number of modes it has detected. This |
| operation is mandatory. |
| </para> |
| <para> |
| When adding modes manually the driver creates each mode with a call to |
| <function>drm_mode_create</function> and must fill the following fields. |
| <itemizedlist> |
| <listitem> |
| <synopsis>__u32 type;</synopsis> |
| <para> |
| Mode type bitmask, a combination of |
| <variablelist> |
| <varlistentry> |
| <term>DRM_MODE_TYPE_BUILTIN</term> |
| <listitem><para>not used?</para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_TYPE_CLOCK_C</term> |
| <listitem><para>not used?</para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_TYPE_CRTC_C</term> |
| <listitem><para>not used?</para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term> |
| DRM_MODE_TYPE_PREFERRED - The preferred mode for the connector |
| </term> |
| <listitem> |
| <para>not used?</para> |
| </listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_TYPE_DEFAULT</term> |
| <listitem><para>not used?</para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_TYPE_USERDEF</term> |
| <listitem><para>not used?</para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_TYPE_DRIVER</term> |
| <listitem> |
| <para> |
| The mode has been created by the driver (as opposed to |
| to user-created modes). |
| </para> |
| </listitem> |
| </varlistentry> |
| </variablelist> |
| Drivers must set the DRM_MODE_TYPE_DRIVER bit for all modes they |
| create, and set the DRM_MODE_TYPE_PREFERRED bit for the preferred |
| mode. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>__u32 clock;</synopsis> |
| <para>Pixel clock frequency in kHz unit</para> |
| </listitem> |
| <listitem> |
| <synopsis>__u16 hdisplay, hsync_start, hsync_end, htotal; |
| __u16 vdisplay, vsync_start, vsync_end, vtotal;</synopsis> |
| <para>Horizontal and vertical timing information</para> |
| <screen><![CDATA[ |
| Active Front Sync Back |
| Region Porch Porch |
| <-----------------------><----------------><-------------><--------------> |
| |
| //////////////////////| |
| ////////////////////// | |
| ////////////////////// |.................. ................ |
| _______________ |
| |
| <----- [hv]display -----> |
| <------------- [hv]sync_start ------------> |
| <--------------------- [hv]sync_end ---------------------> |
| <-------------------------------- [hv]total -----------------------------> |
| ]]></screen> |
| </listitem> |
| <listitem> |
| <synopsis>__u16 hskew; |
| __u16 vscan;</synopsis> |
| <para>Unknown</para> |
| </listitem> |
| <listitem> |
| <synopsis>__u32 flags;</synopsis> |
| <para> |
| Mode flags, a combination of |
| <variablelist> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_PHSYNC</term> |
| <listitem><para> |
| Horizontal sync is active high |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_NHSYNC</term> |
| <listitem><para> |
| Horizontal sync is active low |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_PVSYNC</term> |
| <listitem><para> |
| Vertical sync is active high |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_NVSYNC</term> |
| <listitem><para> |
| Vertical sync is active low |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_INTERLACE</term> |
| <listitem><para> |
| Mode is interlaced |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_DBLSCAN</term> |
| <listitem><para> |
| Mode uses doublescan |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_CSYNC</term> |
| <listitem><para> |
| Mode uses composite sync |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_PCSYNC</term> |
| <listitem><para> |
| Composite sync is active high |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_NCSYNC</term> |
| <listitem><para> |
| Composite sync is active low |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_HSKEW</term> |
| <listitem><para> |
| hskew provided (not used?) |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_BCAST</term> |
| <listitem><para> |
| not used? |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_PIXMUX</term> |
| <listitem><para> |
| not used? |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_DBLCLK</term> |
| <listitem><para> |
| not used? |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_FLAG_CLKDIV2</term> |
| <listitem><para> |
| ? |
| </para></listitem> |
| </varlistentry> |
| </variablelist> |
| </para> |
| <para> |
| Note that modes marked with the INTERLACE or DBLSCAN flags will be |
| filtered out by |
| <function>drm_helper_probe_single_connector_modes</function> if |
| the connector's <structfield>interlace_allowed</structfield> or |
| <structfield>doublescan_allowed</structfield> field is set to 0. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>char name[DRM_DISPLAY_MODE_LEN];</synopsis> |
| <para> |
| Mode name. The driver must call |
| <function>drm_mode_set_name</function> to fill the mode name from |
| <structfield>hdisplay</structfield>, |
| <structfield>vdisplay</structfield> and interlace flag after |
| filling the corresponding fields. |
| </para> |
| </listitem> |
| </itemizedlist> |
| </para> |
| <para> |
| The <structfield>vrefresh</structfield> value is computed by |
| <function>drm_helper_probe_single_connector_modes</function>. |
| </para> |
| <para> |
| When parsing EDID data, <function>drm_add_edid_modes</function> fill the |
| connector <structfield>display_info</structfield> |
| <structfield>width_mm</structfield> and |
| <structfield>height_mm</structfield> fields. When creating modes |
| manually the <methodname>get_modes</methodname> helper operation must |
| set the <structfield>display_info</structfield> |
| <structfield>width_mm</structfield> and |
| <structfield>height_mm</structfield> fields if they haven't been set |
| already (for instance at initialization time when a fixed-size panel is |
| attached to the connector). The mode <structfield>width_mm</structfield> |
| and <structfield>height_mm</structfield> fields are only used internally |
| during EDID parsing and should not be set when creating modes manually. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>int (*mode_valid)(struct drm_connector *connector, |
| struct drm_display_mode *mode);</synopsis> |
| <para> |
| Verify whether a mode is valid for the connector. Return MODE_OK for |
| supported modes and one of the enum drm_mode_status values (MODE_*) |
| for unsupported modes. This operation is mandatory. |
| </para> |
| <para> |
| As the mode rejection reason is currently not used beside for |
| immediately removing the unsupported mode, an implementation can |
| return MODE_BAD regardless of the exact reason why the mode is not |
| valid. |
| </para> |
| <note><para> |
| Note that the <methodname>mode_valid</methodname> helper operation is |
| only called for modes detected by the device, and |
| <emphasis>not</emphasis> for modes set by the user through the CRTC |
| <methodname>set_config</methodname> operation. |
| </para></note> |
| </listitem> |
| </itemizedlist> |
| </sect2> |
| <sect2> |
| <title>Modeset Helper Functions Reference</title> |
| !Edrivers/gpu/drm/drm_crtc_helper.c |
| </sect2> |
| <sect2> |
| <title>fbdev Helper Functions Reference</title> |
| !Pdrivers/gpu/drm/drm_fb_helper.c fbdev helpers |
| !Edrivers/gpu/drm/drm_fb_helper.c |
| !Iinclude/drm/drm_fb_helper.h |
| </sect2> |
| <sect2> |
| <title>Display Port Helper Functions Reference</title> |
| !Pdrivers/gpu/drm/drm_dp_helper.c dp helpers |
| !Iinclude/drm/drm_dp_helper.h |
| !Edrivers/gpu/drm/drm_dp_helper.c |
| </sect2> |
| <sect2> |
| <title>EDID Helper Functions Reference</title> |
| !Edrivers/gpu/drm/drm_edid.c |
| </sect2> |
| <sect2> |
| <title>Rectangle Utilities Reference</title> |
| !Pinclude/drm/drm_rect.h rect utils |
| !Iinclude/drm/drm_rect.h |
| !Edrivers/gpu/drm/drm_rect.c |
| </sect2> |
| <sect2> |
| <title>Flip-work Helper Reference</title> |
| !Pinclude/drm/drm_flip_work.h flip utils |
| !Iinclude/drm/drm_flip_work.h |
| !Edrivers/gpu/drm/drm_flip_work.c |
| </sect2> |
| <sect2> |
| <title>VMA Offset Manager</title> |
| !Pdrivers/gpu/drm/drm_vma_manager.c vma offset manager |
| !Edrivers/gpu/drm/drm_vma_manager.c |
| !Iinclude/drm/drm_vma_manager.h |
| </sect2> |
| </sect1> |
| |
| <!-- Internals: kms properties --> |
| |
| <sect1 id="drm-kms-properties"> |
| <title>KMS Properties</title> |
| <para> |
| Drivers may need to expose additional parameters to applications than |
| those described in the previous sections. KMS supports attaching |
| properties to CRTCs, connectors and planes and offers a userspace API to |
| list, get and set the property values. |
| </para> |
| <para> |
| Properties are identified by a name that uniquely defines the property |
| purpose, and store an associated value. For all property types except blob |
| properties the value is a 64-bit unsigned integer. |
| </para> |
| <para> |
| KMS differentiates between properties and property instances. Drivers |
| first create properties and then create and associate individual instances |
| of those properties to objects. A property can be instantiated multiple |
| times and associated with different objects. Values are stored in property |
| instances, and all other property information are stored in the propery |
| and shared between all instances of the property. |
| </para> |
| <para> |
| Every property is created with a type that influences how the KMS core |
| handles the property. Supported property types are |
| <variablelist> |
| <varlistentry> |
| <term>DRM_MODE_PROP_RANGE</term> |
| <listitem><para>Range properties report their minimum and maximum |
| admissible values. The KMS core verifies that values set by |
| application fit in that range.</para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_PROP_ENUM</term> |
| <listitem><para>Enumerated properties take a numerical value that |
| ranges from 0 to the number of enumerated values defined by the |
| property minus one, and associate a free-formed string name to each |
| value. Applications can retrieve the list of defined value-name pairs |
| and use the numerical value to get and set property instance values. |
| </para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_PROP_BITMASK</term> |
| <listitem><para>Bitmask properties are enumeration properties that |
| additionally restrict all enumerated values to the 0..63 range. |
| Bitmask property instance values combine one or more of the |
| enumerated bits defined by the property.</para></listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_MODE_PROP_BLOB</term> |
| <listitem><para>Blob properties store a binary blob without any format |
| restriction. The binary blobs are created as KMS standalone objects, |
| and blob property instance values store the ID of their associated |
| blob object.</para> |
| <para>Blob properties are only used for the connector EDID property |
| and cannot be created by drivers.</para></listitem> |
| </varlistentry> |
| </variablelist> |
| </para> |
| <para> |
| To create a property drivers call one of the following functions depending |
| on the property type. All property creation functions take property flags |
| and name, as well as type-specific arguments. |
| <itemizedlist> |
| <listitem> |
| <synopsis>struct drm_property *drm_property_create_range(struct drm_device *dev, int flags, |
| const char *name, |
| uint64_t min, uint64_t max);</synopsis> |
| <para>Create a range property with the given minimum and maximum |
| values.</para> |
| </listitem> |
| <listitem> |
| <synopsis>struct drm_property *drm_property_create_enum(struct drm_device *dev, int flags, |
| const char *name, |
| const struct drm_prop_enum_list *props, |
| int num_values);</synopsis> |
| <para>Create an enumerated property. The <parameter>props</parameter> |
| argument points to an array of <parameter>num_values</parameter> |
| value-name pairs.</para> |
| </listitem> |
| <listitem> |
| <synopsis>struct drm_property *drm_property_create_bitmask(struct drm_device *dev, |
| int flags, const char *name, |
| const struct drm_prop_enum_list *props, |
| int num_values);</synopsis> |
| <para>Create a bitmask property. The <parameter>props</parameter> |
| argument points to an array of <parameter>num_values</parameter> |
| value-name pairs.</para> |
| </listitem> |
| </itemizedlist> |
| </para> |
| <para> |
| Properties can additionally be created as immutable, in which case they |
| will be read-only for applications but can be modified by the driver. To |
| create an immutable property drivers must set the DRM_MODE_PROP_IMMUTABLE |
| flag at property creation time. |
| </para> |
| <para> |
| When no array of value-name pairs is readily available at property |
| creation time for enumerated or range properties, drivers can create |
| the property using the <function>drm_property_create</function> function |
| and manually add enumeration value-name pairs by calling the |
| <function>drm_property_add_enum</function> function. Care must be taken to |
| properly specify the property type through the <parameter>flags</parameter> |
| argument. |
| </para> |
| <para> |
| After creating properties drivers can attach property instances to CRTC, |
| connector and plane objects by calling the |
| <function>drm_object_attach_property</function>. The function takes a |
| pointer to the target object, a pointer to the previously created property |
| and an initial instance value. |
| </para> |
| </sect1> |
| |
| <!-- Internals: vertical blanking --> |
| |
| <sect1 id="drm-vertical-blank"> |
| <title>Vertical Blanking</title> |
| <para> |
| Vertical blanking plays a major role in graphics rendering. To achieve |
| tear-free display, users must synchronize page flips and/or rendering to |
| vertical blanking. The DRM API offers ioctls to perform page flips |
| synchronized to vertical blanking and wait for vertical blanking. |
| </para> |
| <para> |
| The DRM core handles most of the vertical blanking management logic, which |
| involves filtering out spurious interrupts, keeping race-free blanking |
| counters, coping with counter wrap-around and resets and keeping use |
| counts. It relies on the driver to generate vertical blanking interrupts |
| and optionally provide a hardware vertical blanking counter. Drivers must |
| implement the following operations. |
| </para> |
| <itemizedlist> |
| <listitem> |
| <synopsis>int (*enable_vblank) (struct drm_device *dev, int crtc); |
| void (*disable_vblank) (struct drm_device *dev, int crtc);</synopsis> |
| <para> |
| Enable or disable vertical blanking interrupts for the given CRTC. |
| </para> |
| </listitem> |
| <listitem> |
| <synopsis>u32 (*get_vblank_counter) (struct drm_device *dev, int crtc);</synopsis> |
| <para> |
| Retrieve the value of the vertical blanking counter for the given |
| CRTC. If the hardware maintains a vertical blanking counter its value |
| should be returned. Otherwise drivers can use the |
| <function>drm_vblank_count</function> helper function to handle this |
| operation. |
| </para> |
| </listitem> |
| </itemizedlist> |
| <para> |
| Drivers must initialize the vertical blanking handling core with a call to |
| <function>drm_vblank_init</function> in their |
| <methodname>load</methodname> operation. The function will set the struct |
| <structname>drm_device</structname> |
| <structfield>vblank_disable_allowed</structfield> field to 0. This will |
| keep vertical blanking interrupts enabled permanently until the first mode |
| set operation, where <structfield>vblank_disable_allowed</structfield> is |
| set to 1. The reason behind this is not clear. Drivers can set the field |
| to 1 after <function>calling drm_vblank_init</function> to make vertical |
| blanking interrupts dynamically managed from the beginning. |
| </para> |
| <para> |
| Vertical blanking interrupts can be enabled by the DRM core or by drivers |
| themselves (for instance to handle page flipping operations). The DRM core |
| maintains a vertical blanking use count to ensure that the interrupts are |
| not disabled while a user still needs them. To increment the use count, |
| drivers call <function>drm_vblank_get</function>. Upon return vertical |
| blanking interrupts are guaranteed to be enabled. |
| </para> |
| <para> |
| To decrement the use count drivers call |
| <function>drm_vblank_put</function>. Only when the use count drops to zero |
| will the DRM core disable the vertical blanking interrupts after a delay |
| by scheduling a timer. The delay is accessible through the vblankoffdelay |
| module parameter or the <varname>drm_vblank_offdelay</varname> global |
| variable and expressed in milliseconds. Its default value is 5000 ms. |
| </para> |
| <para> |
| When a vertical blanking interrupt occurs drivers only need to call the |
| <function>drm_handle_vblank</function> function to account for the |
| interrupt. |
| </para> |
| <para> |
| Resources allocated by <function>drm_vblank_init</function> must be freed |
| with a call to <function>drm_vblank_cleanup</function> in the driver |
| <methodname>unload</methodname> operation handler. |
| </para> |
| </sect1> |
| |
| <!-- Internals: open/close, file operations and ioctls --> |
| |
| <sect1> |
| <title>Open/Close, File Operations and IOCTLs</title> |
| <sect2> |
| <title>Open and Close</title> |
| <synopsis>int (*firstopen) (struct drm_device *); |
| void (*lastclose) (struct drm_device *); |
| int (*open) (struct drm_device *, struct drm_file *); |
| void (*preclose) (struct drm_device *, struct drm_file *); |
| void (*postclose) (struct drm_device *, struct drm_file *);</synopsis> |
| <abstract>Open and close handlers. None of those methods are mandatory. |
| </abstract> |
| <para> |
| The <methodname>firstopen</methodname> method is called by the DRM core |
| for legacy UMS (User Mode Setting) drivers only when an application |
| opens a device that has no other opened file handle. UMS drivers can |
| implement it to acquire device resources. KMS drivers can't use the |
| method and must acquire resources in the <methodname>load</methodname> |
| method instead. |
| </para> |
| <para> |
| Similarly the <methodname>lastclose</methodname> method is called when |
| the last application holding a file handle opened on the device closes |
| it, for both UMS and KMS drivers. Additionally, the method is also |
| called at module unload time or, for hot-pluggable devices, when the |
| device is unplugged. The <methodname>firstopen</methodname> and |
| <methodname>lastclose</methodname> calls can thus be unbalanced. |
| </para> |
| <para> |
| The <methodname>open</methodname> method is called every time the device |
| is opened by an application. Drivers can allocate per-file private data |
| in this method and store them in the struct |
| <structname>drm_file</structname> <structfield>driver_priv</structfield> |
| field. Note that the <methodname>open</methodname> method is called |
| before <methodname>firstopen</methodname>. |
| </para> |
| <para> |
| The close operation is split into <methodname>preclose</methodname> and |
| <methodname>postclose</methodname> methods. Drivers must stop and |
| cleanup all per-file operations in the <methodname>preclose</methodname> |
| method. For instance pending vertical blanking and page flip events must |
| be cancelled. No per-file operation is allowed on the file handle after |
| returning from the <methodname>preclose</methodname> method. |
| </para> |
| <para> |
| Finally the <methodname>postclose</methodname> method is called as the |
| last step of the close operation, right before calling the |
| <methodname>lastclose</methodname> method if no other open file handle |
| exists for the device. Drivers that have allocated per-file private data |
| in the <methodname>open</methodname> method should free it here. |
| </para> |
| <para> |
| The <methodname>lastclose</methodname> method should restore CRTC and |
| plane properties to default value, so that a subsequent open of the |
| device will not inherit state from the previous user. It can also be |
| used to execute delayed power switching state changes, e.g. in |
| conjunction with the vga-switcheroo infrastructure. Beyond that KMS |
| drivers should not do any further cleanup. Only legacy UMS drivers might |
| need to clean up device state so that the vga console or an independent |
| fbdev driver could take over. |
| </para> |
| </sect2> |
| <sect2> |
| <title>File Operations</title> |
| <synopsis>const struct file_operations *fops</synopsis> |
| <abstract>File operations for the DRM device node.</abstract> |
| <para> |
| Drivers must define the file operations structure that forms the DRM |
| userspace API entry point, even though most of those operations are |
| implemented in the DRM core. The <methodname>open</methodname>, |
| <methodname>release</methodname> and <methodname>ioctl</methodname> |
| operations are handled by |
| <programlisting> |
| .owner = THIS_MODULE, |
| .open = drm_open, |
| .release = drm_release, |
| .unlocked_ioctl = drm_ioctl, |
| #ifdef CONFIG_COMPAT |
| .compat_ioctl = drm_compat_ioctl, |
| #endif |
| </programlisting> |
| </para> |
| <para> |
| Drivers that implement private ioctls that requires 32/64bit |
| compatibility support must provide their own |
| <methodname>compat_ioctl</methodname> handler that processes private |
| ioctls and calls <function>drm_compat_ioctl</function> for core ioctls. |
| </para> |
| <para> |
| The <methodname>read</methodname> and <methodname>poll</methodname> |
| operations provide support for reading DRM events and polling them. They |
| are implemented by |
| <programlisting> |
| .poll = drm_poll, |
| .read = drm_read, |
| .llseek = no_llseek, |
| </programlisting> |
| </para> |
| <para> |
| The memory mapping implementation varies depending on how the driver |
| manages memory. Pre-GEM drivers will use <function>drm_mmap</function>, |
| while GEM-aware drivers will use <function>drm_gem_mmap</function>. See |
| <xref linkend="drm-gem"/>. |
| <programlisting> |
| .mmap = drm_gem_mmap, |
| </programlisting> |
| </para> |
| <para> |
| No other file operation is supported by the DRM API. |
| </para> |
| </sect2> |
| <sect2> |
| <title>IOCTLs</title> |
| <synopsis>struct drm_ioctl_desc *ioctls; |
| int num_ioctls;</synopsis> |
| <abstract>Driver-specific ioctls descriptors table.</abstract> |
| <para> |
| Driver-specific ioctls numbers start at DRM_COMMAND_BASE. The ioctls |
| descriptors table is indexed by the ioctl number offset from the base |
| value. Drivers can use the DRM_IOCTL_DEF_DRV() macro to initialize the |
| table entries. |
| </para> |
| <para> |
| <programlisting>DRM_IOCTL_DEF_DRV(ioctl, func, flags)</programlisting> |
| <para> |
| <parameter>ioctl</parameter> is the ioctl name. Drivers must define |
| the DRM_##ioctl and DRM_IOCTL_##ioctl macros to the ioctl number |
| offset from DRM_COMMAND_BASE and the ioctl number respectively. The |
| first macro is private to the device while the second must be exposed |
| to userspace in a public header. |
| </para> |
| <para> |
| <parameter>func</parameter> is a pointer to the ioctl handler function |
| compatible with the <type>drm_ioctl_t</type> type. |
| <programlisting>typedef int drm_ioctl_t(struct drm_device *dev, void *data, |
| struct drm_file *file_priv);</programlisting> |
| </para> |
| <para> |
| <parameter>flags</parameter> is a bitmask combination of the following |
| values. It restricts how the ioctl is allowed to be called. |
| <itemizedlist> |
| <listitem><para> |
| DRM_AUTH - Only authenticated callers allowed |
| </para></listitem> |
| <listitem><para> |
| DRM_MASTER - The ioctl can only be called on the master file |
| handle |
| </para></listitem> |
| <listitem><para> |
| DRM_ROOT_ONLY - Only callers with the SYSADMIN capability allowed |
| </para></listitem> |
| <listitem><para> |
| DRM_CONTROL_ALLOW - The ioctl can only be called on a control |
| device |
| </para></listitem> |
| <listitem><para> |
| DRM_UNLOCKED - The ioctl handler will be called without locking |
| the DRM global mutex |
| </para></listitem> |
| </itemizedlist> |
| </para> |
| </para> |
| </sect2> |
| </sect1> |
| |
| <sect1> |
| <title>Command submission & fencing</title> |
| <para> |
| This should cover a few device-specific command submission |
| implementations. |
| </para> |
| </sect1> |
| |
| <!-- Internals: suspend/resume --> |
| |
| <sect1> |
| <title>Suspend/Resume</title> |
| <para> |
| The DRM core provides some suspend/resume code, but drivers wanting full |
| suspend/resume support should provide save() and restore() functions. |
| These are called at suspend, hibernate, or resume time, and should perform |
| any state save or restore required by your device across suspend or |
| hibernate states. |
| </para> |
| <synopsis>int (*suspend) (struct drm_device *, pm_message_t state); |
| int (*resume) (struct drm_device *);</synopsis> |
| <para> |
| Those are legacy suspend and resume methods. New driver should use the |
| power management interface provided by their bus type (usually through |
| the struct <structname>device_driver</structname> dev_pm_ops) and set |
| these methods to NULL. |
| </para> |
| </sect1> |
| |
| <sect1> |
| <title>DMA services</title> |
| <para> |
| This should cover how DMA mapping etc. is supported by the core. |
| These functions are deprecated and should not be used. |
| </para> |
| </sect1> |
| </chapter> |
| |
| <!-- TODO |
| |
| - Add a glossary |
| - Document the struct_mutex catch-all lock |
| - Document connector properties |
| |
| - Why is the load method optional? |
| - What are drivers supposed to set the initial display state to, and how? |
| Connector's DPMS states are not initialized and are thus equal to |
| DRM_MODE_DPMS_ON. The fbcon compatibility layer calls |
| drm_helper_disable_unused_functions(), which disables unused encoders and |
| CRTCs, but doesn't touch the connectors' DPMS state, and |
| drm_helper_connector_dpms() in reaction to fbdev blanking events. Do drivers |
| that don't implement (or just don't use) fbcon compatibility need to call |
| those functions themselves? |
| - KMS drivers must call drm_vblank_pre_modeset() and drm_vblank_post_modeset() |
| around mode setting. Should this be done in the DRM core? |
| - vblank_disable_allowed is set to 1 in the first drm_vblank_post_modeset() |
| call and never set back to 0. It seems to be safe to permanently set it to 1 |
| in drm_vblank_init() for KMS driver, and it might be safe for UMS drivers as |
| well. This should be investigated. |
| - crtc and connector .save and .restore operations are only used internally in |
| drivers, should they be removed from the core? |
| - encoder mid-layer .save and .restore operations are only used internally in |
| drivers, should they be removed from the core? |
| - encoder mid-layer .detect operation is only used internally in drivers, |
| should it be removed from the core? |
| --> |
| |
| <!-- External interfaces --> |
| |
| <chapter id="drmExternals"> |
| <title>Userland interfaces</title> |
| <para> |
| The DRM core exports several interfaces to applications, |
| generally intended to be used through corresponding libdrm |
| wrapper functions. In addition, drivers export device-specific |
| interfaces for use by userspace drivers & device-aware |
| applications through ioctls and sysfs files. |
| </para> |
| <para> |
| External interfaces include: memory mapping, context management, |
| DMA operations, AGP management, vblank control, fence |
| management, memory management, and output management. |
| </para> |
| <para> |
| Cover generic ioctls and sysfs layout here. We only need high-level |
| info, since man pages should cover the rest. |
| </para> |
| |
| <!-- External: render nodes --> |
| |
| <sect1> |
| <title>Render nodes</title> |
| <para> |
| DRM core provides multiple character-devices for user-space to use. |
| Depending on which device is opened, user-space can perform a different |
| set of operations (mainly ioctls). The primary node is always created |
| and called <term>card<num></term>. Additionally, a currently |
| unused control node, called <term>controlD<num></term> is also |
| created. The primary node provides all legacy operations and |
| historically was the only interface used by userspace. With KMS, the |
| control node was introduced. However, the planned KMS control interface |
| has never been written and so the control node stays unused to date. |
| </para> |
| <para> |
| With the increased use of offscreen renderers and GPGPU applications, |
| clients no longer require running compositors or graphics servers to |
| make use of a GPU. But the DRM API required unprivileged clients to |
| authenticate to a DRM-Master prior to getting GPU access. To avoid this |
| step and to grant clients GPU access without authenticating, render |
| nodes were introduced. Render nodes solely serve render clients, that |
| is, no modesetting or privileged ioctls can be issued on render nodes. |
| Only non-global rendering commands are allowed. If a driver supports |
| render nodes, it must advertise it via the <term>DRIVER_RENDER</term> |
| DRM driver capability. If not supported, the primary node must be used |
| for render clients together with the legacy drmAuth authentication |
| procedure. |
| </para> |
| <para> |
| If a driver advertises render node support, DRM core will create a |
| separate render node called <term>renderD<num></term>. There will |
| be one render node per device. No ioctls except PRIME-related ioctls |
| will be allowed on this node. Especially <term>GEM_OPEN</term> will be |
| explicitly prohibited. Render nodes are designed to avoid the |
| buffer-leaks, which occur if clients guess the flink names or mmap |
| offsets on the legacy interface. Additionally to this basic interface, |
| drivers must mark their driver-dependent render-only ioctls as |
| <term>DRM_RENDER_ALLOW</term> so render clients can use them. Driver |
| authors must be careful not to allow any privileged ioctls on render |
| nodes. |
| </para> |
| <para> |
| With render nodes, user-space can now control access to the render node |
| via basic file-system access-modes. A running graphics server which |
| authenticates clients on the privileged primary/legacy node is no longer |
| required. Instead, a client can open the render node and is immediately |
| granted GPU access. Communication between clients (or servers) is done |
| via PRIME. FLINK from render node to legacy node is not supported. New |
| clients must not use the insecure FLINK interface. |
| </para> |
| <para> |
| Besides dropping all modeset/global ioctls, render nodes also drop the |
| DRM-Master concept. There is no reason to associate render clients with |
| a DRM-Master as they are independent of any graphics server. Besides, |
| they must work without any running master, anyway. |
| Drivers must be able to run without a master object if they support |
| render nodes. If, on the other hand, a driver requires shared state |
| between clients which is visible to user-space and accessible beyond |
| open-file boundaries, they cannot support render nodes. |
| </para> |
| </sect1> |
| |
| <!-- External: vblank handling --> |
| |
| <sect1> |
| <title>VBlank event handling</title> |
| <para> |
| The DRM core exposes two vertical blank related ioctls: |
| <variablelist> |
| <varlistentry> |
| <term>DRM_IOCTL_WAIT_VBLANK</term> |
| <listitem> |
| <para> |
| This takes a struct drm_wait_vblank structure as its argument, |
| and it is used to block or request a signal when a specified |
| vblank event occurs. |
| </para> |
| </listitem> |
| </varlistentry> |
| <varlistentry> |
| <term>DRM_IOCTL_MODESET_CTL</term> |
| <listitem> |
| <para> |
| This should be called by application level drivers before and |
| after mode setting, since on many devices the vertical blank |
| counter is reset at that time. Internally, the DRM snapshots |
| the last vblank count when the ioctl is called with the |
| _DRM_PRE_MODESET command, so that the counter won't go backwards |
| (which is dealt with when _DRM_POST_MODESET is used). |
| </para> |
| </listitem> |
| </varlistentry> |
| </variablelist> |
| <!--!Edrivers/char/drm/drm_irq.c--> |
| </para> |
| </sect1> |
| |
| </chapter> |
| |
| <!-- API reference --> |
| |
| <appendix id="drmDriverApi"> |
| <title>DRM Driver API</title> |
| <para> |
| Include auto-generated API reference here (need to reference it |
| from paragraphs above too). |
| </para> |
| </appendix> |
| |
| </book> |