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Jesse Barnes2d2ef822009-10-26 13:06:31 -07001<?xml version="1.0" encoding="UTF-8"?>
2<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
4
5<book id="drmDevelopersGuide">
6 <bookinfo>
7 <title>Linux DRM Developer's Guide</title>
8
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02009 <authorgroup>
10 <author>
11 <firstname>Jesse</firstname>
12 <surname>Barnes</surname>
13 <contrib>Initial version</contrib>
14 <affiliation>
15 <orgname>Intel Corporation</orgname>
16 <address>
17 <email>jesse.barnes@intel.com</email>
18 </address>
19 </affiliation>
20 </author>
21 <author>
22 <firstname>Laurent</firstname>
23 <surname>Pinchart</surname>
24 <contrib>Driver internals</contrib>
25 <affiliation>
26 <orgname>Ideas on board SPRL</orgname>
27 <address>
28 <email>laurent.pinchart@ideasonboard.com</email>
29 </address>
30 </affiliation>
31 </author>
32 </authorgroup>
33
Jesse Barnes2d2ef822009-10-26 13:06:31 -070034 <copyright>
35 <year>2008-2009</year>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +020036 <year>2012</year>
37 <holder>Intel Corporation</holder>
38 <holder>Laurent Pinchart</holder>
Jesse Barnes2d2ef822009-10-26 13:06:31 -070039 </copyright>
40
41 <legalnotice>
42 <para>
43 The contents of this file may be used under the terms of the GNU
44 General Public License version 2 (the "GPL") as distributed in
45 the kernel source COPYING file.
46 </para>
47 </legalnotice>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +020048
49 <revhistory>
50 <!-- Put document revisions here, newest first. -->
51 <revision>
52 <revnumber>1.0</revnumber>
53 <date>2012-07-13</date>
54 <authorinitials>LP</authorinitials>
55 <revremark>Added extensive documentation about driver internals.
56 </revremark>
57 </revision>
58 </revhistory>
Jesse Barnes2d2ef822009-10-26 13:06:31 -070059 </bookinfo>
60
61<toc></toc>
62
63 <!-- Introduction -->
64
65 <chapter id="drmIntroduction">
66 <title>Introduction</title>
67 <para>
68 The Linux DRM layer contains code intended to support the needs
69 of complex graphics devices, usually containing programmable
70 pipelines well suited to 3D graphics acceleration. Graphics
Michael Wittenf11aca02011-08-25 17:21:31 +000071 drivers in the kernel may make use of DRM functions to make
Jesse Barnes2d2ef822009-10-26 13:06:31 -070072 tasks like memory management, interrupt handling and DMA easier,
73 and provide a uniform interface to applications.
74 </para>
75 <para>
76 A note on versions: this guide covers features found in the DRM
77 tree, including the TTM memory manager, output configuration and
78 mode setting, and the new vblank internals, in addition to all
79 the regular features found in current kernels.
80 </para>
81 <para>
82 [Insert diagram of typical DRM stack here]
83 </para>
84 </chapter>
85
86 <!-- Internals -->
87
88 <chapter id="drmInternals">
89 <title>DRM Internals</title>
90 <para>
91 This chapter documents DRM internals relevant to driver authors
92 and developers working to add support for the latest features to
93 existing drivers.
94 </para>
95 <para>
Michael Wittena78f6782011-08-25 17:18:08 +000096 First, we go over some typical driver initialization
Jesse Barnes2d2ef822009-10-26 13:06:31 -070097 requirements, like setting up command buffers, creating an
98 initial output configuration, and initializing core services.
Michael Wittena78f6782011-08-25 17:18:08 +000099 Subsequent sections cover core internals in more detail,
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700100 providing implementation notes and examples.
101 </para>
102 <para>
103 The DRM layer provides several services to graphics drivers,
104 many of them driven by the application interfaces it provides
105 through libdrm, the library that wraps most of the DRM ioctls.
106 These include vblank event handling, memory
107 management, output management, framebuffer management, command
108 submission &amp; fencing, suspend/resume support, and DMA
109 services.
110 </para>
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700111
112 <!-- Internals: driver init -->
113
114 <sect1>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200115 <title>Driver Initialization</title>
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700116 <para>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200117 At the core of every DRM driver is a <structname>drm_driver</structname>
118 structure. Drivers typically statically initialize a drm_driver structure,
119 and then pass it to one of the <function>drm_*_init()</function> functions
120 to register it with the DRM subsystem.
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700121 </para>
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700122 <para>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200123 The <structname>drm_driver</structname> structure contains static
124 information that describes the driver and features it supports, and
125 pointers to methods that the DRM core will call to implement the DRM API.
126 We will first go through the <structname>drm_driver</structname> static
127 information fields, and will then describe individual operations in
128 details as they get used in later sections.
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700129 </para>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200130 <sect2>
131 <title>Driver Information</title>
132 <sect3>
133 <title>Driver Features</title>
134 <para>
135 Drivers inform the DRM core about their requirements and supported
136 features by setting appropriate flags in the
137 <structfield>driver_features</structfield> field. Since those flags
138 influence the DRM core behaviour since registration time, most of them
139 must be set to registering the <structname>drm_driver</structname>
140 instance.
141 </para>
142 <synopsis>u32 driver_features;</synopsis>
143 <variablelist>
144 <title>Driver Feature Flags</title>
145 <varlistentry>
146 <term>DRIVER_USE_AGP</term>
147 <listitem><para>
148 Driver uses AGP interface, the DRM core will manage AGP resources.
149 </para></listitem>
150 </varlistentry>
151 <varlistentry>
152 <term>DRIVER_REQUIRE_AGP</term>
153 <listitem><para>
154 Driver needs AGP interface to function. AGP initialization failure
155 will become a fatal error.
156 </para></listitem>
157 </varlistentry>
158 <varlistentry>
159 <term>DRIVER_USE_MTRR</term>
160 <listitem><para>
161 Driver uses MTRR interface for mapping memory, the DRM core will
162 manage MTRR resources. Deprecated.
163 </para></listitem>
164 </varlistentry>
165 <varlistentry>
166 <term>DRIVER_PCI_DMA</term>
167 <listitem><para>
168 Driver is capable of PCI DMA, mapping of PCI DMA buffers to
169 userspace will be enabled. Deprecated.
170 </para></listitem>
171 </varlistentry>
172 <varlistentry>
173 <term>DRIVER_SG</term>
174 <listitem><para>
175 Driver can perform scatter/gather DMA, allocation and mapping of
176 scatter/gather buffers will be enabled. Deprecated.
177 </para></listitem>
178 </varlistentry>
179 <varlistentry>
180 <term>DRIVER_HAVE_DMA</term>
181 <listitem><para>
182 Driver supports DMA, the userspace DMA API will be supported.
183 Deprecated.
184 </para></listitem>
185 </varlistentry>
186 <varlistentry>
187 <term>DRIVER_HAVE_IRQ</term><term>DRIVER_IRQ_SHARED</term>
188 <listitem><para>
189 DRIVER_HAVE_IRQ indicates whether the driver has an IRQ handler. The
190 DRM core will automatically register an interrupt handler when the
191 flag is set. DRIVER_IRQ_SHARED indicates whether the device &amp;
192 handler support shared IRQs (note that this is required of PCI
193 drivers).
194 </para></listitem>
195 </varlistentry>
196 <varlistentry>
197 <term>DRIVER_IRQ_VBL</term>
198 <listitem><para>Unused. Deprecated.</para></listitem>
199 </varlistentry>
200 <varlistentry>
201 <term>DRIVER_DMA_QUEUE</term>
202 <listitem><para>
203 Should be set if the driver queues DMA requests and completes them
204 asynchronously. Deprecated.
205 </para></listitem>
206 </varlistentry>
207 <varlistentry>
208 <term>DRIVER_FB_DMA</term>
209 <listitem><para>
210 Driver supports DMA to/from the framebuffer, mapping of frambuffer
211 DMA buffers to userspace will be supported. Deprecated.
212 </para></listitem>
213 </varlistentry>
214 <varlistentry>
215 <term>DRIVER_IRQ_VBL2</term>
216 <listitem><para>Unused. Deprecated.</para></listitem>
217 </varlistentry>
218 <varlistentry>
219 <term>DRIVER_GEM</term>
220 <listitem><para>
221 Driver use the GEM memory manager.
222 </para></listitem>
223 </varlistentry>
224 <varlistentry>
225 <term>DRIVER_MODESET</term>
226 <listitem><para>
227 Driver supports mode setting interfaces (KMS).
228 </para></listitem>
229 </varlistentry>
230 <varlistentry>
231 <term>DRIVER_PRIME</term>
232 <listitem><para>
233 Driver implements DRM PRIME buffer sharing.
234 </para></listitem>
235 </varlistentry>
236 </variablelist>
237 </sect3>
238 <sect3>
239 <title>Major, Minor and Patchlevel</title>
240 <synopsis>int major;
241int minor;
242int patchlevel;</synopsis>
243 <para>
244 The DRM core identifies driver versions by a major, minor and patch
245 level triplet. The information is printed to the kernel log at
246 initialization time and passed to userspace through the
247 DRM_IOCTL_VERSION ioctl.
248 </para>
249 <para>
250 The major and minor numbers are also used to verify the requested driver
251 API version passed to DRM_IOCTL_SET_VERSION. When the driver API changes
252 between minor versions, applications can call DRM_IOCTL_SET_VERSION to
253 select a specific version of the API. If the requested major isn't equal
254 to the driver major, or the requested minor is larger than the driver
255 minor, the DRM_IOCTL_SET_VERSION call will return an error. Otherwise
256 the driver's set_version() method will be called with the requested
257 version.
258 </para>
259 </sect3>
260 <sect3>
261 <title>Name, Description and Date</title>
262 <synopsis>char *name;
263char *desc;
264char *date;</synopsis>
265 <para>
266 The driver name is printed to the kernel log at initialization time,
267 used for IRQ registration and passed to userspace through
268 DRM_IOCTL_VERSION.
269 </para>
270 <para>
271 The driver description is a purely informative string passed to
272 userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by
273 the kernel.
274 </para>
275 <para>
276 The driver date, formatted as YYYYMMDD, is meant to identify the date of
277 the latest modification to the driver. However, as most drivers fail to
278 update it, its value is mostly useless. The DRM core prints it to the
279 kernel log at initialization time and passes it to userspace through the
280 DRM_IOCTL_VERSION ioctl.
281 </para>
282 </sect3>
283 </sect2>
284 <sect2>
285 <title>Driver Load</title>
286 <para>
287 The <methodname>load</methodname> method is the driver and device
288 initialization entry point. The method is responsible for allocating and
289 initializing driver private data, specifying supported performance
290 counters, performing resource allocation and mapping (e.g. acquiring
291 clocks, mapping registers or allocating command buffers), initializing
292 the memory manager (<xref linkend="drm-memory-management"/>), installing
293 the IRQ handler (<xref linkend="drm-irq-registration"/>), setting up
294 vertical blanking handling (<xref linkend="drm-vertical-blank"/>), mode
295 setting (<xref linkend="drm-mode-setting"/>) and initial output
296 configuration (<xref linkend="drm-kms-init"/>).
297 </para>
298 <note><para>
299 If compatibility is a concern (e.g. with drivers converted over from
300 User Mode Setting to Kernel Mode Setting), care must be taken to prevent
301 device initialization and control that is incompatible with currently
302 active userspace drivers. For instance, if user level mode setting
303 drivers are in use, it would be problematic to perform output discovery
304 &amp; configuration at load time. Likewise, if user-level drivers
305 unaware of memory management are in use, memory management and command
306 buffer setup may need to be omitted. These requirements are
307 driver-specific, and care needs to be taken to keep both old and new
308 applications and libraries working.
309 </para></note>
310 <synopsis>int (*load) (struct drm_device *, unsigned long flags);</synopsis>
311 <para>
312 The method takes two arguments, a pointer to the newly created
313 <structname>drm_device</structname> and flags. The flags are used to
314 pass the <structfield>driver_data</structfield> field of the device id
315 corresponding to the device passed to <function>drm_*_init()</function>.
316 Only PCI devices currently use this, USB and platform DRM drivers have
317 their <methodname>load</methodname> method called with flags to 0.
318 </para>
319 <sect3>
320 <title>Driver Private &amp; Performance Counters</title>
321 <para>
322 The driver private hangs off the main
323 <structname>drm_device</structname> structure and can be used for
324 tracking various device-specific bits of information, like register
325 offsets, command buffer status, register state for suspend/resume, etc.
326 At load time, a driver may simply allocate one and set
327 <structname>drm_device</structname>.<structfield>dev_priv</structfield>
328 appropriately; it should be freed and
329 <structname>drm_device</structname>.<structfield>dev_priv</structfield>
330 set to NULL when the driver is unloaded.
331 </para>
332 <para>
333 DRM supports several counters which were used for rough performance
334 characterization. This stat counter system is deprecated and should not
335 be used. If performance monitoring is desired, the developer should
336 investigate and potentially enhance the kernel perf and tracing
337 infrastructure to export GPU related performance information for
338 consumption by performance monitoring tools and applications.
339 </para>
340 </sect3>
341 <sect3 id="drm-irq-registration">
342 <title>IRQ Registration</title>
343 <para>
344 The DRM core tries to facilitate IRQ handler registration and
345 unregistration by providing <function>drm_irq_install</function> and
346 <function>drm_irq_uninstall</function> functions. Those functions only
347 support a single interrupt per device.
348 </para>
349 <!--!Fdrivers/char/drm/drm_irq.c drm_irq_install-->
350 <para>
351 Both functions get the device IRQ by calling
352 <function>drm_dev_to_irq</function>. This inline function will call a
353 bus-specific operation to retrieve the IRQ number. For platform devices,
354 <function>platform_get_irq</function>(..., 0) is used to retrieve the
355 IRQ number.
356 </para>
357 <para>
358 <function>drm_irq_install</function> starts by calling the
359 <methodname>irq_preinstall</methodname> driver operation. The operation
360 is optional and must make sure that the interrupt will not get fired by
361 clearing all pending interrupt flags or disabling the interrupt.
362 </para>
363 <para>
364 The IRQ will then be requested by a call to
365 <function>request_irq</function>. If the DRIVER_IRQ_SHARED driver
366 feature flag is set, a shared (IRQF_SHARED) IRQ handler will be
367 requested.
368 </para>
369 <para>
370 The IRQ handler function must be provided as the mandatory irq_handler
371 driver operation. It will get passed directly to
372 <function>request_irq</function> and thus has the same prototype as all
373 IRQ handlers. It will get called with a pointer to the DRM device as the
374 second argument.
375 </para>
376 <para>
377 Finally the function calls the optional
378 <methodname>irq_postinstall</methodname> driver operation. The operation
379 usually enables interrupts (excluding the vblank interrupt, which is
380 enabled separately), but drivers may choose to enable/disable interrupts
381 at a different time.
382 </para>
383 <para>
384 <function>drm_irq_uninstall</function> is similarly used to uninstall an
385 IRQ handler. It starts by waking up all processes waiting on a vblank
386 interrupt to make sure they don't hang, and then calls the optional
387 <methodname>irq_uninstall</methodname> driver operation. The operation
388 must disable all hardware interrupts. Finally the function frees the IRQ
389 by calling <function>free_irq</function>.
390 </para>
391 </sect3>
392 <sect3>
393 <title>Memory Manager Initialization</title>
394 <para>
395 Every DRM driver requires a memory manager which must be initialized at
396 load time. DRM currently contains two memory managers, the Translation
397 Table Manager (TTM) and the Graphics Execution Manager (GEM).
398 This document describes the use of the GEM memory manager only. See
399 <xref linkend="drm-memory-management"/> for details.
400 </para>
401 </sect3>
402 <sect3>
403 <title>Miscellaneous Device Configuration</title>
404 <para>
405 Another task that may be necessary for PCI devices during configuration
406 is mapping the video BIOS. On many devices, the VBIOS describes device
407 configuration, LCD panel timings (if any), and contains flags indicating
408 device state. Mapping the BIOS can be done using the pci_map_rom() call,
409 a convenience function that takes care of mapping the actual ROM,
410 whether it has been shadowed into memory (typically at address 0xc0000)
411 or exists on the PCI device in the ROM BAR. Note that after the ROM has
412 been mapped and any necessary information has been extracted, it should
413 be unmapped; on many devices, the ROM address decoder is shared with
414 other BARs, so leaving it mapped could cause undesired behaviour like
415 hangs or memory corruption.
416 <!--!Fdrivers/pci/rom.c pci_map_rom-->
417 </para>
418 </sect3>
419 </sect2>
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700420 </sect1>
421
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200422 <!-- Internals: memory management -->
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700423
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200424 <sect1 id="drm-memory-management">
425 <title>Memory management</title>
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700426 <para>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200427 Modern Linux systems require large amount of graphics memory to store
428 frame buffers, textures, vertices and other graphics-related data. Given
429 the very dynamic nature of many of that data, managing graphics memory
430 efficiently is thus crucial for the graphics stack and plays a central
431 role in the DRM infrastructure.
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700432 </para>
433 <para>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200434 The DRM core includes two memory managers, namely Translation Table Maps
435 (TTM) and Graphics Execution Manager (GEM). TTM was the first DRM memory
436 manager to be developed and tried to be a one-size-fits-them all
437 solution. It provides a single userspace API to accomodate the need of
438 all hardware, supporting both Unified Memory Architecture (UMA) devices
439 and devices with dedicated video RAM (i.e. most discrete video cards).
440 This resulted in a large, complex piece of code that turned out to be
441 hard to use for driver development.
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700442 </para>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200443 <para>
444 GEM started as an Intel-sponsored project in reaction to TTM's
445 complexity. Its design philosophy is completely different: instead of
446 providing a solution to every graphics memory-related problems, GEM
447 identified common code between drivers and created a support library to
448 share it. GEM has simpler initialization and execution requirements than
449 TTM, but has no video RAM management capabitilies and is thus limited to
450 UMA devices.
451 </para>
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700452 <sect2>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200453 <title>The Translation Table Manager (TTM)</title>
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700454 <para>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200455 TTM design background and information belongs here.
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700456 </para>
457 <sect3>
458 <title>TTM initialization</title>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200459 <warning><para>This section is outdated.</para></warning>
460 <para>
461 Drivers wishing to support TTM must fill out a drm_bo_driver
462 structure. The structure contains several fields with function
463 pointers for initializing the TTM, allocating and freeing memory,
464 waiting for command completion and fence synchronization, and memory
465 migration. See the radeon_ttm.c file for an example of usage.
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700466 </para>
467 <para>
468 The ttm_global_reference structure is made up of several fields:
469 </para>
470 <programlisting>
471 struct ttm_global_reference {
472 enum ttm_global_types global_type;
473 size_t size;
474 void *object;
475 int (*init) (struct ttm_global_reference *);
476 void (*release) (struct ttm_global_reference *);
477 };
478 </programlisting>
479 <para>
480 There should be one global reference structure for your memory
481 manager as a whole, and there will be others for each object
482 created by the memory manager at runtime. Your global TTM should
483 have a type of TTM_GLOBAL_TTM_MEM. The size field for the global
484 object should be sizeof(struct ttm_mem_global), and the init and
Michael Wittena5294e02011-08-29 18:05:52 +0000485 release hooks should point at your driver-specific init and
Michael Wittena78f6782011-08-25 17:18:08 +0000486 release routines, which probably eventually call
Michael Witten005d7f42011-08-25 19:02:52 +0000487 ttm_mem_global_init and ttm_mem_global_release, respectively.
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700488 </para>
489 <para>
490 Once your global TTM accounting structure is set up and initialized
Michael Wittenae63d792011-08-25 19:19:18 +0000491 by calling ttm_global_item_ref() on it,
Michael Witten1c86de22011-08-25 19:14:26 +0000492 you need to create a buffer object TTM to
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700493 provide a pool for buffer object allocation by clients and the
494 kernel itself. The type of this object should be TTM_GLOBAL_TTM_BO,
495 and its size should be sizeof(struct ttm_bo_global). Again,
Michael Wittena5294e02011-08-29 18:05:52 +0000496 driver-specific init and release functions may be provided,
Michael Wittenae63d792011-08-25 19:19:18 +0000497 likely eventually calling ttm_bo_global_init() and
498 ttm_bo_global_release(), respectively. Also, like the previous
499 object, ttm_global_item_ref() is used to create an initial reference
Nicolas Kaiserce04cc02010-05-28 07:33:49 +0200500 count for the TTM, which will call your initialization function.
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700501 </para>
502 </sect3>
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700503 </sect2>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200504 <sect2 id="drm-gem">
505 <title>The Graphics Execution Manager (GEM)</title>
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700506 <para>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200507 The GEM design approach has resulted in a memory manager that doesn't
508 provide full coverage of all (or even all common) use cases in its
509 userspace or kernel API. GEM exposes a set of standard memory-related
510 operations to userspace and a set of helper functions to drivers, and let
511 drivers implement hardware-specific operations with their own private API.
512 </para>
513 <para>
514 The GEM userspace API is described in the
515 <ulink url="http://lwn.net/Articles/283798/"><citetitle>GEM - the Graphics
516 Execution Manager</citetitle></ulink> article on LWN. While slightly
517 outdated, the document provides a good overview of the GEM API principles.
518 Buffer allocation and read and write operations, described as part of the
519 common GEM API, are currently implemented using driver-specific ioctls.
520 </para>
521 <para>
522 GEM is data-agnostic. It manages abstract buffer objects without knowing
523 what individual buffers contain. APIs that require knowledge of buffer
524 contents or purpose, such as buffer allocation or synchronization
525 primitives, are thus outside of the scope of GEM and must be implemented
526 using driver-specific ioctls.
527 </para>
528 <para>
529 On a fundamental level, GEM involves several operations:
Michael Witten327d6fb2011-08-25 20:18:14 +0000530 <itemizedlist>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200531 <listitem>Memory allocation and freeing</listitem>
532 <listitem>Command execution</listitem>
533 <listitem>Aperture management at command execution time</listitem>
Michael Witten327d6fb2011-08-25 20:18:14 +0000534 </itemizedlist>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200535 Buffer object allocation is relatively straightforward and largely
536 provided by Linux's shmem layer, which provides memory to back each
537 object.
538 </para>
539 <para>
540 Device-specific operations, such as command execution, pinning, buffer
541 read &amp; write, mapping, and domain ownership transfers are left to
542 driver-specific ioctls.
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700543 </para>
544 <sect3>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200545 <title>GEM Initialization</title>
546 <para>
547 Drivers that use GEM must set the DRIVER_GEM bit in the struct
548 <structname>drm_driver</structname>
549 <structfield>driver_features</structfield> field. The DRM core will
550 then automatically initialize the GEM core before calling the
551 <methodname>load</methodname> operation. Behind the scene, this will
552 create a DRM Memory Manager object which provides an address space
553 pool for object allocation.
554 </para>
555 <para>
556 In a KMS configuration, drivers need to allocate and initialize a
557 command ring buffer following core GEM initialization if required by
558 the hardware. UMA devices usually have what is called a "stolen"
559 memory region, which provides space for the initial framebuffer and
560 large, contiguous memory regions required by the device. This space is
561 typically not managed by GEM, and must be initialized separately into
562 its own DRM MM object.
563 </para>
564 </sect3>
565 <sect3>
566 <title>GEM Objects Creation</title>
567 <para>
568 GEM splits creation of GEM objects and allocation of the memory that
569 backs them in two distinct operations.
570 </para>
571 <para>
572 GEM objects are represented by an instance of struct
573 <structname>drm_gem_object</structname>. Drivers usually need to extend
574 GEM objects with private information and thus create a driver-specific
575 GEM object structure type that embeds an instance of struct
576 <structname>drm_gem_object</structname>.
577 </para>
578 <para>
579 To create a GEM object, a driver allocates memory for an instance of its
580 specific GEM object type and initializes the embedded struct
581 <structname>drm_gem_object</structname> with a call to
582 <function>drm_gem_object_init</function>. The function takes a pointer to
583 the DRM device, a pointer to the GEM object and the buffer object size
584 in bytes.
585 </para>
586 <para>
587 GEM uses shmem to allocate anonymous pageable memory.
588 <function>drm_gem_object_init</function> will create an shmfs file of
589 the requested size and store it into the struct
590 <structname>drm_gem_object</structname> <structfield>filp</structfield>
591 field. The memory is used as either main storage for the object when the
592 graphics hardware uses system memory directly or as a backing store
593 otherwise.
594 </para>
595 <para>
596 Drivers are responsible for the actual physical pages allocation by
597 calling <function>shmem_read_mapping_page_gfp</function> for each page.
598 Note that they can decide to allocate pages when initializing the GEM
599 object, or to delay allocation until the memory is needed (for instance
600 when a page fault occurs as a result of a userspace memory access or
601 when the driver needs to start a DMA transfer involving the memory).
602 </para>
603 <para>
604 Anonymous pageable memory allocation is not always desired, for instance
605 when the hardware requires physically contiguous system memory as is
606 often the case in embedded devices. Drivers can create GEM objects with
607 no shmfs backing (called private GEM objects) by initializing them with
608 a call to <function>drm_gem_private_object_init</function> instead of
609 <function>drm_gem_object_init</function>. Storage for private GEM
610 objects must be managed by drivers.
611 </para>
612 <para>
613 Drivers that do not need to extend GEM objects with private information
614 can call the <function>drm_gem_object_alloc</function> function to
615 allocate and initialize a struct <structname>drm_gem_object</structname>
616 instance. The GEM core will call the optional driver
617 <methodname>gem_init_object</methodname> operation after initializing
618 the GEM object with <function>drm_gem_object_init</function>.
619 <synopsis>int (*gem_init_object) (struct drm_gem_object *obj);</synopsis>
620 </para>
621 <para>
622 No alloc-and-init function exists for private GEM objects.
623 </para>
624 </sect3>
625 <sect3>
626 <title>GEM Objects Lifetime</title>
627 <para>
628 All GEM objects are reference-counted by the GEM core. References can be
629 acquired and release by <function>calling drm_gem_object_reference</function>
630 and <function>drm_gem_object_unreference</function> respectively. The
631 caller must hold the <structname>drm_device</structname>
632 <structfield>struct_mutex</structfield> lock. As a convenience, GEM
633 provides the <function>drm_gem_object_reference_unlocked</function> and
634 <function>drm_gem_object_unreference_unlocked</function> functions that
635 can be called without holding the lock.
636 </para>
637 <para>
638 When the last reference to a GEM object is released the GEM core calls
639 the <structname>drm_driver</structname>
640 <methodname>gem_free_object</methodname> operation. That operation is
641 mandatory for GEM-enabled drivers and must free the GEM object and all
642 associated resources.
643 </para>
644 <para>
645 <synopsis>void (*gem_free_object) (struct drm_gem_object *obj);</synopsis>
646 Drivers are responsible for freeing all GEM object resources, including
647 the resources created by the GEM core. If an mmap offset has been
648 created for the object (in which case
649 <structname>drm_gem_object</structname>::<structfield>map_list</structfield>::<structfield>map</structfield>
650 is not NULL) it must be freed by a call to
651 <function>drm_gem_free_mmap_offset</function>. The shmfs backing store
652 must be released by calling <function>drm_gem_object_release</function>
653 (that function can safely be called if no shmfs backing store has been
654 created).
655 </para>
656 </sect3>
657 <sect3>
658 <title>GEM Objects Naming</title>
659 <para>
660 Communication between userspace and the kernel refers to GEM objects
661 using local handles, global names or, more recently, file descriptors.
662 All of those are 32-bit integer values; the usual Linux kernel limits
663 apply to the file descriptors.
664 </para>
665 <para>
666 GEM handles are local to a DRM file. Applications get a handle to a GEM
667 object through a driver-specific ioctl, and can use that handle to refer
668 to the GEM object in other standard or driver-specific ioctls. Closing a
669 DRM file handle frees all its GEM handles and dereferences the
670 associated GEM objects.
671 </para>
672 <para>
673 To create a handle for a GEM object drivers call
674 <function>drm_gem_handle_create</function>. The function takes a pointer
675 to the DRM file and the GEM object and returns a locally unique handle.
676 When the handle is no longer needed drivers delete it with a call to
677 <function>drm_gem_handle_delete</function>. Finally the GEM object
678 associated with a handle can be retrieved by a call to
679 <function>drm_gem_object_lookup</function>.
680 </para>
681 <para>
682 Handles don't take ownership of GEM objects, they only take a reference
683 to the object that will be dropped when the handle is destroyed. To
684 avoid leaking GEM objects, drivers must make sure they drop the
685 reference(s) they own (such as the initial reference taken at object
686 creation time) as appropriate, without any special consideration for the
687 handle. For example, in the particular case of combined GEM object and
688 handle creation in the implementation of the
689 <methodname>dumb_create</methodname> operation, drivers must drop the
690 initial reference to the GEM object before returning the handle.
691 </para>
692 <para>
693 GEM names are similar in purpose to handles but are not local to DRM
694 files. They can be passed between processes to reference a GEM object
695 globally. Names can't be used directly to refer to objects in the DRM
696 API, applications must convert handles to names and names to handles
697 using the DRM_IOCTL_GEM_FLINK and DRM_IOCTL_GEM_OPEN ioctls
698 respectively. The conversion is handled by the DRM core without any
699 driver-specific support.
700 </para>
701 <para>
702 Similar to global names, GEM file descriptors are also used to share GEM
703 objects across processes. They offer additional security: as file
704 descriptors must be explictly sent over UNIX domain sockets to be shared
705 between applications, they can't be guessed like the globally unique GEM
706 names.
707 </para>
708 <para>
709 Drivers that support GEM file descriptors, also known as the DRM PRIME
710 API, must set the DRIVER_PRIME bit in the struct
711 <structname>drm_driver</structname>
712 <structfield>driver_features</structfield> field, and implement the
713 <methodname>prime_handle_to_fd</methodname> and
714 <methodname>prime_fd_to_handle</methodname> operations.
715 </para>
716 <para>
717 <synopsis>int (*prime_handle_to_fd)(struct drm_device *dev,
718 struct drm_file *file_priv, uint32_t handle,
719 uint32_t flags, int *prime_fd);
720 int (*prime_fd_to_handle)(struct drm_device *dev,
721 struct drm_file *file_priv, int prime_fd,
722 uint32_t *handle);</synopsis>
723 Those two operations convert a handle to a PRIME file descriptor and
724 vice versa. Drivers must use the kernel dma-buf buffer sharing framework
725 to manage the PRIME file descriptors.
726 </para>
727 <para>
728 While non-GEM drivers must implement the operations themselves, GEM
729 drivers must use the <function>drm_gem_prime_handle_to_fd</function>
730 and <function>drm_gem_prime_fd_to_handle</function> helper functions.
731 Those helpers rely on the driver
732 <methodname>gem_prime_export</methodname> and
733 <methodname>gem_prime_import</methodname> operations to create a dma-buf
734 instance from a GEM object (dma-buf exporter role) and to create a GEM
735 object from a dma-buf instance (dma-buf importer role).
736 </para>
737 <para>
738 <synopsis>struct dma_buf * (*gem_prime_export)(struct drm_device *dev,
739 struct drm_gem_object *obj,
740 int flags);
741 struct drm_gem_object * (*gem_prime_import)(struct drm_device *dev,
742 struct dma_buf *dma_buf);</synopsis>
743 These two operations are mandatory for GEM drivers that support DRM
744 PRIME.
745 </para>
Aaron Plattner89177642013-01-15 20:47:42 +0000746 <sect4>
747 <title>DRM PRIME Helper Functions Reference</title>
748!Pdrivers/gpu/drm/drm_prime.c PRIME Helpers
749 </sect4>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200750 </sect3>
751 <sect3 id="drm-gem-objects-mapping">
752 <title>GEM Objects Mapping</title>
753 <para>
754 Because mapping operations are fairly heavyweight GEM favours
755 read/write-like access to buffers, implemented through driver-specific
756 ioctls, over mapping buffers to userspace. However, when random access
757 to the buffer is needed (to perform software rendering for instance),
758 direct access to the object can be more efficient.
759 </para>
760 <para>
761 The mmap system call can't be used directly to map GEM objects, as they
762 don't have their own file handle. Two alternative methods currently
763 co-exist to map GEM objects to userspace. The first method uses a
764 driver-specific ioctl to perform the mapping operation, calling
765 <function>do_mmap</function> under the hood. This is often considered
766 dubious, seems to be discouraged for new GEM-enabled drivers, and will
767 thus not be described here.
768 </para>
769 <para>
770 The second method uses the mmap system call on the DRM file handle.
771 <synopsis>void *mmap(void *addr, size_t length, int prot, int flags, int fd,
772 off_t offset);</synopsis>
773 DRM identifies the GEM object to be mapped by a fake offset passed
774 through the mmap offset argument. Prior to being mapped, a GEM object
775 must thus be associated with a fake offset. To do so, drivers must call
776 <function>drm_gem_create_mmap_offset</function> on the object. The
777 function allocates a fake offset range from a pool and stores the
778 offset divided by PAGE_SIZE in
779 <literal>obj-&gt;map_list.hash.key</literal>. Care must be taken not to
780 call <function>drm_gem_create_mmap_offset</function> if a fake offset
781 has already been allocated for the object. This can be tested by
782 <literal>obj-&gt;map_list.map</literal> being non-NULL.
783 </para>
784 <para>
785 Once allocated, the fake offset value
786 (<literal>obj-&gt;map_list.hash.key &lt;&lt; PAGE_SHIFT</literal>)
787 must be passed to the application in a driver-specific way and can then
788 be used as the mmap offset argument.
789 </para>
790 <para>
791 The GEM core provides a helper method <function>drm_gem_mmap</function>
792 to handle object mapping. The method can be set directly as the mmap
793 file operation handler. It will look up the GEM object based on the
794 offset value and set the VMA operations to the
795 <structname>drm_driver</structname> <structfield>gem_vm_ops</structfield>
796 field. Note that <function>drm_gem_mmap</function> doesn't map memory to
797 userspace, but relies on the driver-provided fault handler to map pages
798 individually.
799 </para>
800 <para>
801 To use <function>drm_gem_mmap</function>, drivers must fill the struct
802 <structname>drm_driver</structname> <structfield>gem_vm_ops</structfield>
803 field with a pointer to VM operations.
804 </para>
805 <para>
806 <synopsis>struct vm_operations_struct *gem_vm_ops
807
808 struct vm_operations_struct {
809 void (*open)(struct vm_area_struct * area);
810 void (*close)(struct vm_area_struct * area);
811 int (*fault)(struct vm_area_struct *vma, struct vm_fault *vmf);
812 };</synopsis>
813 </para>
814 <para>
815 The <methodname>open</methodname> and <methodname>close</methodname>
816 operations must update the GEM object reference count. Drivers can use
817 the <function>drm_gem_vm_open</function> and
818 <function>drm_gem_vm_close</function> helper functions directly as open
819 and close handlers.
820 </para>
821 <para>
822 The fault operation handler is responsible for mapping individual pages
823 to userspace when a page fault occurs. Depending on the memory
824 allocation scheme, drivers can allocate pages at fault time, or can
825 decide to allocate memory for the GEM object at the time the object is
826 created.
827 </para>
828 <para>
829 Drivers that want to map the GEM object upfront instead of handling page
830 faults can implement their own mmap file operation handler.
831 </para>
832 </sect3>
833 <sect3>
834 <title>Dumb GEM Objects</title>
835 <para>
836 The GEM API doesn't standardize GEM objects creation and leaves it to
837 driver-specific ioctls. While not an issue for full-fledged graphics
838 stacks that include device-specific userspace components (in libdrm for
839 instance), this limit makes DRM-based early boot graphics unnecessarily
840 complex.
841 </para>
842 <para>
843 Dumb GEM objects partly alleviate the problem by providing a standard
844 API to create dumb buffers suitable for scanout, which can then be used
845 to create KMS frame buffers.
846 </para>
847 <para>
848 To support dumb GEM objects drivers must implement the
849 <methodname>dumb_create</methodname>,
850 <methodname>dumb_destroy</methodname> and
851 <methodname>dumb_map_offset</methodname> operations.
852 </para>
853 <itemizedlist>
854 <listitem>
855 <synopsis>int (*dumb_create)(struct drm_file *file_priv, struct drm_device *dev,
856 struct drm_mode_create_dumb *args);</synopsis>
857 <para>
858 The <methodname>dumb_create</methodname> operation creates a GEM
859 object suitable for scanout based on the width, height and depth
860 from the struct <structname>drm_mode_create_dumb</structname>
861 argument. It fills the argument's <structfield>handle</structfield>,
862 <structfield>pitch</structfield> and <structfield>size</structfield>
863 fields with a handle for the newly created GEM object and its line
864 pitch and size in bytes.
865 </para>
866 </listitem>
867 <listitem>
868 <synopsis>int (*dumb_destroy)(struct drm_file *file_priv, struct drm_device *dev,
869 uint32_t handle);</synopsis>
870 <para>
871 The <methodname>dumb_destroy</methodname> operation destroys a dumb
872 GEM object created by <methodname>dumb_create</methodname>.
873 </para>
874 </listitem>
875 <listitem>
876 <synopsis>int (*dumb_map_offset)(struct drm_file *file_priv, struct drm_device *dev,
877 uint32_t handle, uint64_t *offset);</synopsis>
878 <para>
879 The <methodname>dumb_map_offset</methodname> operation associates an
880 mmap fake offset with the GEM object given by the handle and returns
881 it. Drivers must use the
882 <function>drm_gem_create_mmap_offset</function> function to
883 associate the fake offset as described in
884 <xref linkend="drm-gem-objects-mapping"/>.
885 </para>
886 </listitem>
887 </itemizedlist>
888 </sect3>
889 <sect3>
890 <title>Memory Coherency</title>
891 <para>
892 When mapped to the device or used in a command buffer, backing pages
893 for an object are flushed to memory and marked write combined so as to
894 be coherent with the GPU. Likewise, if the CPU accesses an object
895 after the GPU has finished rendering to the object, then the object
896 must be made coherent with the CPU's view of memory, usually involving
897 GPU cache flushing of various kinds. This core CPU&lt;-&gt;GPU
898 coherency management is provided by a device-specific ioctl, which
899 evaluates an object's current domain and performs any necessary
900 flushing or synchronization to put the object into the desired
901 coherency domain (note that the object may be busy, i.e. an active
902 render target; in that case, setting the domain blocks the client and
903 waits for rendering to complete before performing any necessary
904 flushing operations).
905 </para>
906 </sect3>
907 <sect3>
908 <title>Command Execution</title>
909 <para>
910 Perhaps the most important GEM function for GPU devices is providing a
911 command execution interface to clients. Client programs construct
912 command buffers containing references to previously allocated memory
913 objects, and then submit them to GEM. At that point, GEM takes care to
914 bind all the objects into the GTT, execute the buffer, and provide
915 necessary synchronization between clients accessing the same buffers.
916 This often involves evicting some objects from the GTT and re-binding
917 others (a fairly expensive operation), and providing relocation
918 support which hides fixed GTT offsets from clients. Clients must take
919 care not to submit command buffers that reference more objects than
920 can fit in the GTT; otherwise, GEM will reject them and no rendering
921 will occur. Similarly, if several objects in the buffer require fence
922 registers to be allocated for correct rendering (e.g. 2D blits on
923 pre-965 chips), care must be taken not to require more fence registers
924 than are available to the client. Such resource management should be
925 abstracted from the client in libdrm.
926 </para>
927 </sect3>
928 </sect2>
929 </sect1>
930
931 <!-- Internals: mode setting -->
932
933 <sect1 id="drm-mode-setting">
934 <title>Mode Setting</title>
935 <para>
936 Drivers must initialize the mode setting core by calling
937 <function>drm_mode_config_init</function> on the DRM device. The function
938 initializes the <structname>drm_device</structname>
939 <structfield>mode_config</structfield> field and never fails. Once done,
940 mode configuration must be setup by initializing the following fields.
941 </para>
942 <itemizedlist>
943 <listitem>
944 <synopsis>int min_width, min_height;
945int max_width, max_height;</synopsis>
946 <para>
947 Minimum and maximum width and height of the frame buffers in pixel
948 units.
Jesse Barnes2d2ef822009-10-26 13:06:31 -0700949 </para>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +0200950 </listitem>
951 <listitem>
952 <synopsis>struct drm_mode_config_funcs *funcs;</synopsis>
953 <para>Mode setting functions.</para>
954 </listitem>
955 </itemizedlist>
956 <sect2>
957 <title>Frame Buffer Creation</title>
958 <synopsis>struct drm_framebuffer *(*fb_create)(struct drm_device *dev,
959 struct drm_file *file_priv,
960 struct drm_mode_fb_cmd2 *mode_cmd);</synopsis>
961 <para>
962 Frame buffers are abstract memory objects that provide a source of
963 pixels to scanout to a CRTC. Applications explicitly request the
964 creation of frame buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls and
965 receive an opaque handle that can be passed to the KMS CRTC control,
966 plane configuration and page flip functions.
967 </para>
968 <para>
969 Frame buffers rely on the underneath memory manager for low-level memory
970 operations. When creating a frame buffer applications pass a memory
971 handle (or a list of memory handles for multi-planar formats) through
972 the <parameter>drm_mode_fb_cmd2</parameter> argument. This document
973 assumes that the driver uses GEM, those handles thus reference GEM
974 objects.
975 </para>
976 <para>
977 Drivers must first validate the requested frame buffer parameters passed
978 through the mode_cmd argument. In particular this is where invalid
979 sizes, pixel formats or pitches can be caught.
980 </para>
981 <para>
982 If the parameters are deemed valid, drivers then create, initialize and
983 return an instance of struct <structname>drm_framebuffer</structname>.
984 If desired the instance can be embedded in a larger driver-specific
Daniel Vetter5d7a9512013-01-04 22:31:20 +0100985 structure. Drivers must fill its <structfield>width</structfield>,
986 <structfield>height</structfield>, <structfield>pitches</structfield>,
987 <structfield>offsets</structfield>, <structfield>depth</structfield>,
988 <structfield>bits_per_pixel</structfield> and
989 <structfield>pixel_format</structfield> fields from the values passed
990 through the <parameter>drm_mode_fb_cmd2</parameter> argument. They
991 should call the <function>drm_helper_mode_fill_fb_struct</function>
992 helper function to do so.
993 </para>
994
995 <para>
996 The initailization of the new framebuffer instance is finalized with a
997 call to <function>drm_framebuffer_init</function> which takes a pointer
998 to DRM frame buffer operations (struct
999 <structname>drm_framebuffer_funcs</structname>). Note that this function
1000 publishes the framebuffer and so from this point on it can be accessed
1001 concurrently from other threads. Hence it must be the last step in the
1002 driver's framebuffer initialization sequence. Frame buffer operations
1003 are
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02001004 <itemizedlist>
1005 <listitem>
1006 <synopsis>int (*create_handle)(struct drm_framebuffer *fb,
1007 struct drm_file *file_priv, unsigned int *handle);</synopsis>
1008 <para>
1009 Create a handle to the frame buffer underlying memory object. If
1010 the frame buffer uses a multi-plane format, the handle will
1011 reference the memory object associated with the first plane.
1012 </para>
1013 <para>
1014 Drivers call <function>drm_gem_handle_create</function> to create
1015 the handle.
1016 </para>
1017 </listitem>
1018 <listitem>
1019 <synopsis>void (*destroy)(struct drm_framebuffer *framebuffer);</synopsis>
1020 <para>
1021 Destroy the frame buffer object and frees all associated
1022 resources. Drivers must call
1023 <function>drm_framebuffer_cleanup</function> to free resources
1024 allocated by the DRM core for the frame buffer object, and must
1025 make sure to unreference all memory objects associated with the
1026 frame buffer. Handles created by the
1027 <methodname>create_handle</methodname> operation are released by
1028 the DRM core.
1029 </para>
1030 </listitem>
1031 <listitem>
1032 <synopsis>int (*dirty)(struct drm_framebuffer *framebuffer,
1033 struct drm_file *file_priv, unsigned flags, unsigned color,
1034 struct drm_clip_rect *clips, unsigned num_clips);</synopsis>
1035 <para>
1036 This optional operation notifies the driver that a region of the
1037 frame buffer has changed in response to a DRM_IOCTL_MODE_DIRTYFB
1038 ioctl call.
1039 </para>
1040 </listitem>
1041 </itemizedlist>
1042 </para>
1043 <para>
Daniel Vetter5d7a9512013-01-04 22:31:20 +01001044 The lifetime of a drm framebuffer is controlled with a reference count,
1045 drivers can grab additional references with
1046 <function>drm_framebuffer_reference</function> </para> and drop them
1047 again with <function>drm_framebuffer_unreference</function>. For
1048 driver-private framebuffers for which the last reference is never
1049 dropped (e.g. for the fbdev framebuffer when the struct
1050 <structname>drm_framebuffer</structname> is embedded into the fbdev
1051 helper struct) drivers can manually clean up a framebuffer at module
1052 unload time with
1053 <function>drm_framebuffer_unregister_private</function>.
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02001054 </sect2>
1055 <sect2>
1056 <title>Output Polling</title>
1057 <synopsis>void (*output_poll_changed)(struct drm_device *dev);</synopsis>
1058 <para>
1059 This operation notifies the driver that the status of one or more
1060 connectors has changed. Drivers that use the fb helper can just call the
1061 <function>drm_fb_helper_hotplug_event</function> function to handle this
1062 operation.
1063 </para>
1064 </sect2>
Daniel Vetter5d7a9512013-01-04 22:31:20 +01001065 <sect2>
1066 <title>Locking</title>
1067 <para>
1068 Beside some lookup structures with their own locking (which is hidden
1069 behind the interface functions) most of the modeset state is protected
1070 by the <code>dev-&lt;mode_config.lock</code> mutex and additionally
1071 per-crtc locks to allow cursor updates, pageflips and similar operations
1072 to occur concurrently with background tasks like output detection.
1073 Operations which cross domains like a full modeset always grab all
1074 locks. Drivers there need to protect resources shared between crtcs with
1075 additional locking. They also need to be careful to always grab the
1076 relevant crtc locks if a modset functions touches crtc state, e.g. for
1077 load detection (which does only grab the <code>mode_config.lock</code>
1078 to allow concurrent screen updates on live crtcs).
1079 </para>
1080 </sect2>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02001081 </sect1>
1082
1083 <!-- Internals: kms initialization and cleanup -->
1084
1085 <sect1 id="drm-kms-init">
1086 <title>KMS Initialization and Cleanup</title>
1087 <para>
1088 A KMS device is abstracted and exposed as a set of planes, CRTCs, encoders
1089 and connectors. KMS drivers must thus create and initialize all those
1090 objects at load time after initializing mode setting.
1091 </para>
1092 <sect2>
1093 <title>CRTCs (struct <structname>drm_crtc</structname>)</title>
1094 <para>
1095 A CRTC is an abstraction representing a part of the chip that contains a
1096 pointer to a scanout buffer. Therefore, the number of CRTCs available
1097 determines how many independent scanout buffers can be active at any
1098 given time. The CRTC structure contains several fields to support this:
1099 a pointer to some video memory (abstracted as a frame buffer object), a
1100 display mode, and an (x, y) offset into the video memory to support
1101 panning or configurations where one piece of video memory spans multiple
1102 CRTCs.
1103 </para>
1104 <sect3>
1105 <title>CRTC Initialization</title>
1106 <para>
1107 A KMS device must create and register at least one struct
1108 <structname>drm_crtc</structname> instance. The instance is allocated
1109 and zeroed by the driver, possibly as part of a larger structure, and
1110 registered with a call to <function>drm_crtc_init</function> with a
1111 pointer to CRTC functions.
1112 </para>
1113 </sect3>
1114 <sect3>
1115 <title>CRTC Operations</title>
1116 <sect4>
1117 <title>Set Configuration</title>
1118 <synopsis>int (*set_config)(struct drm_mode_set *set);</synopsis>
1119 <para>
1120 Apply a new CRTC configuration to the device. The configuration
1121 specifies a CRTC, a frame buffer to scan out from, a (x,y) position in
1122 the frame buffer, a display mode and an array of connectors to drive
1123 with the CRTC if possible.
1124 </para>
1125 <para>
1126 If the frame buffer specified in the configuration is NULL, the driver
1127 must detach all encoders connected to the CRTC and all connectors
1128 attached to those encoders and disable them.
1129 </para>
1130 <para>
1131 This operation is called with the mode config lock held.
1132 </para>
1133 <note><para>
1134 FIXME: How should set_config interact with DPMS? If the CRTC is
1135 suspended, should it be resumed?
1136 </para></note>
1137 </sect4>
1138 <sect4>
1139 <title>Page Flipping</title>
1140 <synopsis>int (*page_flip)(struct drm_crtc *crtc, struct drm_framebuffer *fb,
1141 struct drm_pending_vblank_event *event);</synopsis>
1142 <para>
1143 Schedule a page flip to the given frame buffer for the CRTC. This
1144 operation is called with the mode config mutex held.
1145 </para>
1146 <para>
1147 Page flipping is a synchronization mechanism that replaces the frame
1148 buffer being scanned out by the CRTC with a new frame buffer during
1149 vertical blanking, avoiding tearing. When an application requests a page
1150 flip the DRM core verifies that the new frame buffer is large enough to
1151 be scanned out by the CRTC in the currently configured mode and then
1152 calls the CRTC <methodname>page_flip</methodname> operation with a
1153 pointer to the new frame buffer.
1154 </para>
1155 <para>
1156 The <methodname>page_flip</methodname> operation schedules a page flip.
1157 Once any pending rendering targetting the new frame buffer has
1158 completed, the CRTC will be reprogrammed to display that frame buffer
1159 after the next vertical refresh. The operation must return immediately
1160 without waiting for rendering or page flip to complete and must block
1161 any new rendering to the frame buffer until the page flip completes.
1162 </para>
1163 <para>
1164 If a page flip is already pending, the
1165 <methodname>page_flip</methodname> operation must return
1166 -<errorname>EBUSY</errorname>.
1167 </para>
1168 <para>
1169 To synchronize page flip to vertical blanking the driver will likely
1170 need to enable vertical blanking interrupts. It should call
1171 <function>drm_vblank_get</function> for that purpose, and call
1172 <function>drm_vblank_put</function> after the page flip completes.
1173 </para>
1174 <para>
1175 If the application has requested to be notified when page flip completes
1176 the <methodname>page_flip</methodname> operation will be called with a
1177 non-NULL <parameter>event</parameter> argument pointing to a
1178 <structname>drm_pending_vblank_event</structname> instance. Upon page
Rob Clarkc6eefa12012-10-16 22:48:40 +00001179 flip completion the driver must call <methodname>drm_send_vblank_event</methodname>
1180 to fill in the event and send to wake up any waiting processes.
1181 This can be performed with
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02001182 <programlisting><![CDATA[
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02001183 spin_lock_irqsave(&dev->event_lock, flags);
Rob Clarkc6eefa12012-10-16 22:48:40 +00001184 ...
1185 drm_send_vblank_event(dev, pipe, event);
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02001186 spin_unlock_irqrestore(&dev->event_lock, flags);
1187 ]]></programlisting>
1188 </para>
1189 <note><para>
1190 FIXME: Could drivers that don't need to wait for rendering to complete
1191 just add the event to <literal>dev-&gt;vblank_event_list</literal> and
1192 let the DRM core handle everything, as for "normal" vertical blanking
1193 events?
1194 </para></note>
1195 <para>
1196 While waiting for the page flip to complete, the
1197 <literal>event-&gt;base.link</literal> list head can be used freely by
1198 the driver to store the pending event in a driver-specific list.
1199 </para>
1200 <para>
1201 If the file handle is closed before the event is signaled, drivers must
1202 take care to destroy the event in their
1203 <methodname>preclose</methodname> operation (and, if needed, call
1204 <function>drm_vblank_put</function>).
1205 </para>
1206 </sect4>
1207 <sect4>
1208 <title>Miscellaneous</title>
1209 <itemizedlist>
1210 <listitem>
1211 <synopsis>void (*gamma_set)(struct drm_crtc *crtc, u16 *r, u16 *g, u16 *b,
1212 uint32_t start, uint32_t size);</synopsis>
1213 <para>
1214 Apply a gamma table to the device. The operation is optional.
1215 </para>
1216 </listitem>
1217 <listitem>
1218 <synopsis>void (*destroy)(struct drm_crtc *crtc);</synopsis>
1219 <para>
1220 Destroy the CRTC when not needed anymore. See
1221 <xref linkend="drm-kms-init"/>.
1222 </para>
1223 </listitem>
1224 </itemizedlist>
1225 </sect4>
1226 </sect3>
1227 </sect2>
1228 <sect2>
1229 <title>Planes (struct <structname>drm_plane</structname>)</title>
1230 <para>
1231 A plane represents an image source that can be blended with or overlayed
1232 on top of a CRTC during the scanout process. Planes are associated with
1233 a frame buffer to crop a portion of the image memory (source) and
1234 optionally scale it to a destination size. The result is then blended
1235 with or overlayed on top of a CRTC.
1236 </para>
1237 <sect3>
1238 <title>Plane Initialization</title>
1239 <para>
1240 Planes are optional. To create a plane, a KMS drivers allocates and
1241 zeroes an instances of struct <structname>drm_plane</structname>
1242 (possibly as part of a larger structure) and registers it with a call
1243 to <function>drm_plane_init</function>. The function takes a bitmask
1244 of the CRTCs that can be associated with the plane, a pointer to the
1245 plane functions and a list of format supported formats.
1246 </para>
1247 </sect3>
1248 <sect3>
1249 <title>Plane Operations</title>
1250 <itemizedlist>
1251 <listitem>
1252 <synopsis>int (*update_plane)(struct drm_plane *plane, struct drm_crtc *crtc,
1253 struct drm_framebuffer *fb, int crtc_x, int crtc_y,
1254 unsigned int crtc_w, unsigned int crtc_h,
1255 uint32_t src_x, uint32_t src_y,
1256 uint32_t src_w, uint32_t src_h);</synopsis>
1257 <para>
1258 Enable and configure the plane to use the given CRTC and frame buffer.
1259 </para>
1260 <para>
1261 The source rectangle in frame buffer memory coordinates is given by
1262 the <parameter>src_x</parameter>, <parameter>src_y</parameter>,
1263 <parameter>src_w</parameter> and <parameter>src_h</parameter>
1264 parameters (as 16.16 fixed point values). Devices that don't support
1265 subpixel plane coordinates can ignore the fractional part.
1266 </para>
1267 <para>
1268 The destination rectangle in CRTC coordinates is given by the
1269 <parameter>crtc_x</parameter>, <parameter>crtc_y</parameter>,
1270 <parameter>crtc_w</parameter> and <parameter>crtc_h</parameter>
1271 parameters (as integer values). Devices scale the source rectangle to
1272 the destination rectangle. If scaling is not supported, and the source
1273 rectangle size doesn't match the destination rectangle size, the
1274 driver must return a -<errorname>EINVAL</errorname> error.
1275 </para>
1276 </listitem>
1277 <listitem>
1278 <synopsis>int (*disable_plane)(struct drm_plane *plane);</synopsis>
1279 <para>
1280 Disable the plane. The DRM core calls this method in response to a
1281 DRM_IOCTL_MODE_SETPLANE ioctl call with the frame buffer ID set to 0.
1282 Disabled planes must not be processed by the CRTC.
1283 </para>
1284 </listitem>
1285 <listitem>
1286 <synopsis>void (*destroy)(struct drm_plane *plane);</synopsis>
1287 <para>
1288 Destroy the plane when not needed anymore. See
1289 <xref linkend="drm-kms-init"/>.
1290 </para>
1291 </listitem>
1292 </itemizedlist>
1293 </sect3>
1294 </sect2>
1295 <sect2>
1296 <title>Encoders (struct <structname>drm_encoder</structname>)</title>
1297 <para>
1298 An encoder takes pixel data from a CRTC and converts it to a format
1299 suitable for any attached connectors. On some devices, it may be
1300 possible to have a CRTC send data to more than one encoder. In that
1301 case, both encoders would receive data from the same scanout buffer,
1302 resulting in a "cloned" display configuration across the connectors
1303 attached to each encoder.
1304 </para>
1305 <sect3>
1306 <title>Encoder Initialization</title>
1307 <para>
1308 As for CRTCs, a KMS driver must create, initialize and register at
1309 least one struct <structname>drm_encoder</structname> instance. The
1310 instance is allocated and zeroed by the driver, possibly as part of a
1311 larger structure.
1312 </para>
1313 <para>
1314 Drivers must initialize the struct <structname>drm_encoder</structname>
1315 <structfield>possible_crtcs</structfield> and
1316 <structfield>possible_clones</structfield> fields before registering the
1317 encoder. Both fields are bitmasks of respectively the CRTCs that the
1318 encoder can be connected to, and sibling encoders candidate for cloning.
1319 </para>
1320 <para>
1321 After being initialized, the encoder must be registered with a call to
1322 <function>drm_encoder_init</function>. The function takes a pointer to
1323 the encoder functions and an encoder type. Supported types are
1324 <itemizedlist>
1325 <listitem>
1326 DRM_MODE_ENCODER_DAC for VGA and analog on DVI-I/DVI-A
1327 </listitem>
1328 <listitem>
1329 DRM_MODE_ENCODER_TMDS for DVI, HDMI and (embedded) DisplayPort
1330 </listitem>
1331 <listitem>
1332 DRM_MODE_ENCODER_LVDS for display panels
1333 </listitem>
1334 <listitem>
1335 DRM_MODE_ENCODER_TVDAC for TV output (Composite, S-Video, Component,
1336 SCART)
1337 </listitem>
1338 <listitem>
1339 DRM_MODE_ENCODER_VIRTUAL for virtual machine displays
1340 </listitem>
1341 </itemizedlist>
1342 </para>
1343 <para>
1344 Encoders must be attached to a CRTC to be used. DRM drivers leave
1345 encoders unattached at initialization time. Applications (or the fbdev
1346 compatibility layer when implemented) are responsible for attaching the
1347 encoders they want to use to a CRTC.
1348 </para>
1349 </sect3>
1350 <sect3>
1351 <title>Encoder Operations</title>
1352 <itemizedlist>
1353 <listitem>
1354 <synopsis>void (*destroy)(struct drm_encoder *encoder);</synopsis>
1355 <para>
1356 Called to destroy the encoder when not needed anymore. See
1357 <xref linkend="drm-kms-init"/>.
1358 </para>
1359 </listitem>
1360 </itemizedlist>
1361 </sect3>
1362 </sect2>
1363 <sect2>
1364 <title>Connectors (struct <structname>drm_connector</structname>)</title>
1365 <para>
1366 A connector is the final destination for pixel data on a device, and
1367 usually connects directly to an external display device like a monitor
1368 or laptop panel. A connector can only be attached to one encoder at a
1369 time. The connector is also the structure where information about the
1370 attached display is kept, so it contains fields for display data, EDID
1371 data, DPMS &amp; connection status, and information about modes
1372 supported on the attached displays.
1373 </para>
1374 <sect3>
1375 <title>Connector Initialization</title>
1376 <para>
1377 Finally a KMS driver must create, initialize, register and attach at
1378 least one struct <structname>drm_connector</structname> instance. The
1379 instance is created as other KMS objects and initialized by setting the
1380 following fields.
1381 </para>
1382 <variablelist>
1383 <varlistentry>
1384 <term><structfield>interlace_allowed</structfield></term>
1385 <listitem><para>
1386 Whether the connector can handle interlaced modes.
1387 </para></listitem>
1388 </varlistentry>
1389 <varlistentry>
1390 <term><structfield>doublescan_allowed</structfield></term>
1391 <listitem><para>
1392 Whether the connector can handle doublescan.
1393 </para></listitem>
1394 </varlistentry>
1395 <varlistentry>
1396 <term><structfield>display_info
1397 </structfield></term>
1398 <listitem><para>
1399 Display information is filled from EDID information when a display
1400 is detected. For non hot-pluggable displays such as flat panels in
1401 embedded systems, the driver should initialize the
1402 <structfield>display_info</structfield>.<structfield>width_mm</structfield>
1403 and
1404 <structfield>display_info</structfield>.<structfield>height_mm</structfield>
1405 fields with the physical size of the display.
1406 </para></listitem>
1407 </varlistentry>
1408 <varlistentry>
1409 <term id="drm-kms-connector-polled"><structfield>polled</structfield></term>
1410 <listitem><para>
1411 Connector polling mode, a combination of
1412 <variablelist>
1413 <varlistentry>
1414 <term>DRM_CONNECTOR_POLL_HPD</term>
1415 <listitem><para>
1416 The connector generates hotplug events and doesn't need to be
1417 periodically polled. The CONNECT and DISCONNECT flags must not
1418 be set together with the HPD flag.
1419 </para></listitem>
1420 </varlistentry>
1421 <varlistentry>
1422 <term>DRM_CONNECTOR_POLL_CONNECT</term>
1423 <listitem><para>
1424 Periodically poll the connector for connection.
1425 </para></listitem>
1426 </varlistentry>
1427 <varlistentry>
1428 <term>DRM_CONNECTOR_POLL_DISCONNECT</term>
1429 <listitem><para>
1430 Periodically poll the connector for disconnection.
1431 </para></listitem>
1432 </varlistentry>
1433 </variablelist>
1434 Set to 0 for connectors that don't support connection status
1435 discovery.
1436 </para></listitem>
1437 </varlistentry>
1438 </variablelist>
1439 <para>
1440 The connector is then registered with a call to
1441 <function>drm_connector_init</function> with a pointer to the connector
1442 functions and a connector type, and exposed through sysfs with a call to
1443 <function>drm_sysfs_connector_add</function>.
1444 </para>
1445 <para>
1446 Supported connector types are
1447 <itemizedlist>
1448 <listitem>DRM_MODE_CONNECTOR_VGA</listitem>
1449 <listitem>DRM_MODE_CONNECTOR_DVII</listitem>
1450 <listitem>DRM_MODE_CONNECTOR_DVID</listitem>
1451 <listitem>DRM_MODE_CONNECTOR_DVIA</listitem>
1452 <listitem>DRM_MODE_CONNECTOR_Composite</listitem>
1453 <listitem>DRM_MODE_CONNECTOR_SVIDEO</listitem>
1454 <listitem>DRM_MODE_CONNECTOR_LVDS</listitem>
1455 <listitem>DRM_MODE_CONNECTOR_Component</listitem>
1456 <listitem>DRM_MODE_CONNECTOR_9PinDIN</listitem>
1457 <listitem>DRM_MODE_CONNECTOR_DisplayPort</listitem>
1458 <listitem>DRM_MODE_CONNECTOR_HDMIA</listitem>
1459 <listitem>DRM_MODE_CONNECTOR_HDMIB</listitem>
1460 <listitem>DRM_MODE_CONNECTOR_TV</listitem>
1461 <listitem>DRM_MODE_CONNECTOR_eDP</listitem>
1462 <listitem>DRM_MODE_CONNECTOR_VIRTUAL</listitem>
1463 </itemizedlist>
1464 </para>
1465 <para>
1466 Connectors must be attached to an encoder to be used. For devices that
1467 map connectors to encoders 1:1, the connector should be attached at
1468 initialization time with a call to
1469 <function>drm_mode_connector_attach_encoder</function>. The driver must
1470 also set the <structname>drm_connector</structname>
1471 <structfield>encoder</structfield> field to point to the attached
1472 encoder.
1473 </para>
1474 <para>
1475 Finally, drivers must initialize the connectors state change detection
1476 with a call to <function>drm_kms_helper_poll_init</function>. If at
1477 least one connector is pollable but can't generate hotplug interrupts
1478 (indicated by the DRM_CONNECTOR_POLL_CONNECT and
1479 DRM_CONNECTOR_POLL_DISCONNECT connector flags), a delayed work will
1480 automatically be queued to periodically poll for changes. Connectors
1481 that can generate hotplug interrupts must be marked with the
1482 DRM_CONNECTOR_POLL_HPD flag instead, and their interrupt handler must
1483 call <function>drm_helper_hpd_irq_event</function>. The function will
1484 queue a delayed work to check the state of all connectors, but no
1485 periodic polling will be done.
1486 </para>
1487 </sect3>
1488 <sect3>
1489 <title>Connector Operations</title>
1490 <note><para>
1491 Unless otherwise state, all operations are mandatory.
1492 </para></note>
1493 <sect4>
1494 <title>DPMS</title>
1495 <synopsis>void (*dpms)(struct drm_connector *connector, int mode);</synopsis>
1496 <para>
1497 The DPMS operation sets the power state of a connector. The mode
1498 argument is one of
1499 <itemizedlist>
1500 <listitem><para>DRM_MODE_DPMS_ON</para></listitem>
1501 <listitem><para>DRM_MODE_DPMS_STANDBY</para></listitem>
1502 <listitem><para>DRM_MODE_DPMS_SUSPEND</para></listitem>
1503 <listitem><para>DRM_MODE_DPMS_OFF</para></listitem>
1504 </itemizedlist>
1505 </para>
1506 <para>
1507 In all but DPMS_ON mode the encoder to which the connector is attached
1508 should put the display in low-power mode by driving its signals
1509 appropriately. If more than one connector is attached to the encoder
1510 care should be taken not to change the power state of other displays as
1511 a side effect. Low-power mode should be propagated to the encoders and
1512 CRTCs when all related connectors are put in low-power mode.
1513 </para>
1514 </sect4>
1515 <sect4>
1516 <title>Modes</title>
1517 <synopsis>int (*fill_modes)(struct drm_connector *connector, uint32_t max_width,
1518 uint32_t max_height);</synopsis>
1519 <para>
1520 Fill the mode list with all supported modes for the connector. If the
1521 <parameter>max_width</parameter> and <parameter>max_height</parameter>
1522 arguments are non-zero, the implementation must ignore all modes wider
1523 than <parameter>max_width</parameter> or higher than
1524 <parameter>max_height</parameter>.
1525 </para>
1526 <para>
1527 The connector must also fill in this operation its
1528 <structfield>display_info</structfield>
1529 <structfield>width_mm</structfield> and
1530 <structfield>height_mm</structfield> fields with the connected display
1531 physical size in millimeters. The fields should be set to 0 if the value
1532 isn't known or is not applicable (for instance for projector devices).
1533 </para>
1534 </sect4>
1535 <sect4>
1536 <title>Connection Status</title>
1537 <para>
1538 The connection status is updated through polling or hotplug events when
1539 supported (see <xref linkend="drm-kms-connector-polled"/>). The status
1540 value is reported to userspace through ioctls and must not be used
1541 inside the driver, as it only gets initialized by a call to
1542 <function>drm_mode_getconnector</function> from userspace.
1543 </para>
1544 <synopsis>enum drm_connector_status (*detect)(struct drm_connector *connector,
1545 bool force);</synopsis>
1546 <para>
1547 Check to see if anything is attached to the connector. The
1548 <parameter>force</parameter> parameter is set to false whilst polling or
1549 to true when checking the connector due to user request.
1550 <parameter>force</parameter> can be used by the driver to avoid
1551 expensive, destructive operations during automated probing.
1552 </para>
1553 <para>
1554 Return connector_status_connected if something is connected to the
1555 connector, connector_status_disconnected if nothing is connected and
1556 connector_status_unknown if the connection state isn't known.
1557 </para>
1558 <para>
1559 Drivers should only return connector_status_connected if the connection
1560 status has really been probed as connected. Connectors that can't detect
1561 the connection status, or failed connection status probes, should return
1562 connector_status_unknown.
1563 </para>
1564 </sect4>
1565 <sect4>
1566 <title>Miscellaneous</title>
1567 <itemizedlist>
1568 <listitem>
1569 <synopsis>void (*destroy)(struct drm_connector *connector);</synopsis>
1570 <para>
1571 Destroy the connector when not needed anymore. See
1572 <xref linkend="drm-kms-init"/>.
1573 </para>
1574 </listitem>
1575 </itemizedlist>
1576 </sect4>
1577 </sect3>
1578 </sect2>
1579 <sect2>
1580 <title>Cleanup</title>
1581 <para>
1582 The DRM core manages its objects' lifetime. When an object is not needed
1583 anymore the core calls its destroy function, which must clean up and
1584 free every resource allocated for the object. Every
1585 <function>drm_*_init</function> call must be matched with a
1586 corresponding <function>drm_*_cleanup</function> call to cleanup CRTCs
1587 (<function>drm_crtc_cleanup</function>), planes
1588 (<function>drm_plane_cleanup</function>), encoders
1589 (<function>drm_encoder_cleanup</function>) and connectors
1590 (<function>drm_connector_cleanup</function>). Furthermore, connectors
1591 that have been added to sysfs must be removed by a call to
1592 <function>drm_sysfs_connector_remove</function> before calling
1593 <function>drm_connector_cleanup</function>.
1594 </para>
1595 <para>
1596 Connectors state change detection must be cleanup up with a call to
1597 <function>drm_kms_helper_poll_fini</function>.
1598 </para>
1599 </sect2>
1600 <sect2>
1601 <title>Output discovery and initialization example</title>
1602 <programlisting><![CDATA[
Jesse Barnes2d2ef822009-10-26 13:06:31 -07001603void intel_crt_init(struct drm_device *dev)
1604{
1605 struct drm_connector *connector;
1606 struct intel_output *intel_output;
1607
1608 intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
1609 if (!intel_output)
1610 return;
1611
1612 connector = &intel_output->base;
1613 drm_connector_init(dev, &intel_output->base,
1614 &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
1615
1616 drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
1617 DRM_MODE_ENCODER_DAC);
1618
1619 drm_mode_connector_attach_encoder(&intel_output->base,
1620 &intel_output->enc);
1621
1622 /* Set up the DDC bus. */
1623 intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
1624 if (!intel_output->ddc_bus) {
1625 dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
1626 "failed.\n");
1627 return;
1628 }
1629
1630 intel_output->type = INTEL_OUTPUT_ANALOG;
1631 connector->interlace_allowed = 0;
1632 connector->doublescan_allowed = 0;
1633
1634 drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
1635 drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
1636
1637 drm_sysfs_connector_add(connector);
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02001638}]]></programlisting>
1639 <para>
1640 In the example above (taken from the i915 driver), a CRTC, connector and
1641 encoder combination is created. A device-specific i2c bus is also
1642 created for fetching EDID data and performing monitor detection. Once
1643 the process is complete, the new connector is registered with sysfs to
1644 make its properties available to applications.
1645 </para>
1646 </sect2>
Daniel Vetter065a50ed2012-12-02 00:09:18 +01001647 <sect2>
1648 <title>KMS API Functions</title>
1649!Edrivers/gpu/drm/drm_crtc.c
1650 </sect2>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02001651 </sect1>
1652
Daniel Vettere4949f22012-11-01 14:45:15 +01001653 <!-- Internals: kms helper functions -->
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02001654
1655 <sect1>
Daniel Vettere4949f22012-11-01 14:45:15 +01001656 <title>Mode Setting Helper Functions</title>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02001657 <para>
1658 The CRTC, encoder and connector functions provided by the drivers
1659 implement the DRM API. They're called by the DRM core and ioctl handlers
1660 to handle device state changes and configuration request. As implementing
1661 those functions often requires logic not specific to drivers, mid-layer
1662 helper functions are available to avoid duplicating boilerplate code.
1663 </para>
1664 <para>
1665 The DRM core contains one mid-layer implementation. The mid-layer provides
1666 implementations of several CRTC, encoder and connector functions (called
1667 from the top of the mid-layer) that pre-process requests and call
1668 lower-level functions provided by the driver (at the bottom of the
1669 mid-layer). For instance, the
1670 <function>drm_crtc_helper_set_config</function> function can be used to
1671 fill the struct <structname>drm_crtc_funcs</structname>
1672 <structfield>set_config</structfield> field. When called, it will split
1673 the <methodname>set_config</methodname> operation in smaller, simpler
1674 operations and call the driver to handle them.
1675 </para>
1676 <para>
1677 To use the mid-layer, drivers call <function>drm_crtc_helper_add</function>,
1678 <function>drm_encoder_helper_add</function> and
1679 <function>drm_connector_helper_add</function> functions to install their
1680 mid-layer bottom operations handlers, and fill the
1681 <structname>drm_crtc_funcs</structname>,
1682 <structname>drm_encoder_funcs</structname> and
1683 <structname>drm_connector_funcs</structname> structures with pointers to
1684 the mid-layer top API functions. Installing the mid-layer bottom operation
1685 handlers is best done right after registering the corresponding KMS object.
1686 </para>
1687 <para>
1688 The mid-layer is not split between CRTC, encoder and connector operations.
1689 To use it, a driver must provide bottom functions for all of the three KMS
1690 entities.
1691 </para>
1692 <sect2>
1693 <title>Helper Functions</title>
1694 <itemizedlist>
1695 <listitem>
1696 <synopsis>int drm_crtc_helper_set_config(struct drm_mode_set *set);</synopsis>
1697 <para>
1698 The <function>drm_crtc_helper_set_config</function> helper function
1699 is a CRTC <methodname>set_config</methodname> implementation. It
1700 first tries to locate the best encoder for each connector by calling
1701 the connector <methodname>best_encoder</methodname> helper
1702 operation.
1703 </para>
1704 <para>
1705 After locating the appropriate encoders, the helper function will
1706 call the <methodname>mode_fixup</methodname> encoder and CRTC helper
1707 operations to adjust the requested mode, or reject it completely in
1708 which case an error will be returned to the application. If the new
1709 configuration after mode adjustment is identical to the current
1710 configuration the helper function will return without performing any
1711 other operation.
1712 </para>
1713 <para>
1714 If the adjusted mode is identical to the current mode but changes to
1715 the frame buffer need to be applied, the
1716 <function>drm_crtc_helper_set_config</function> function will call
1717 the CRTC <methodname>mode_set_base</methodname> helper operation. If
1718 the adjusted mode differs from the current mode, or if the
1719 <methodname>mode_set_base</methodname> helper operation is not
1720 provided, the helper function performs a full mode set sequence by
1721 calling the <methodname>prepare</methodname>,
1722 <methodname>mode_set</methodname> and
1723 <methodname>commit</methodname> CRTC and encoder helper operations,
1724 in that order.
1725 </para>
1726 </listitem>
1727 <listitem>
1728 <synopsis>void drm_helper_connector_dpms(struct drm_connector *connector, int mode);</synopsis>
1729 <para>
1730 The <function>drm_helper_connector_dpms</function> helper function
1731 is a connector <methodname>dpms</methodname> implementation that
1732 tracks power state of connectors. To use the function, drivers must
1733 provide <methodname>dpms</methodname> helper operations for CRTCs
1734 and encoders to apply the DPMS state to the device.
1735 </para>
1736 <para>
1737 The mid-layer doesn't track the power state of CRTCs and encoders.
1738 The <methodname>dpms</methodname> helper operations can thus be
1739 called with a mode identical to the currently active mode.
1740 </para>
1741 </listitem>
1742 <listitem>
1743 <synopsis>int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
1744 uint32_t maxX, uint32_t maxY);</synopsis>
1745 <para>
1746 The <function>drm_helper_probe_single_connector_modes</function> helper
1747 function is a connector <methodname>fill_modes</methodname>
1748 implementation that updates the connection status for the connector
1749 and then retrieves a list of modes by calling the connector
1750 <methodname>get_modes</methodname> helper operation.
1751 </para>
1752 <para>
1753 The function filters out modes larger than
1754 <parameter>max_width</parameter> and <parameter>max_height</parameter>
1755 if specified. It then calls the connector
1756 <methodname>mode_valid</methodname> helper operation for each mode in
1757 the probed list to check whether the mode is valid for the connector.
1758 </para>
1759 </listitem>
1760 </itemizedlist>
1761 </sect2>
1762 <sect2>
1763 <title>CRTC Helper Operations</title>
1764 <itemizedlist>
1765 <listitem id="drm-helper-crtc-mode-fixup">
1766 <synopsis>bool (*mode_fixup)(struct drm_crtc *crtc,
1767 const struct drm_display_mode *mode,
1768 struct drm_display_mode *adjusted_mode);</synopsis>
1769 <para>
1770 Let CRTCs adjust the requested mode or reject it completely. This
1771 operation returns true if the mode is accepted (possibly after being
1772 adjusted) or false if it is rejected.
1773 </para>
1774 <para>
1775 The <methodname>mode_fixup</methodname> operation should reject the
1776 mode if it can't reasonably use it. The definition of "reasonable"
1777 is currently fuzzy in this context. One possible behaviour would be
1778 to set the adjusted mode to the panel timings when a fixed-mode
1779 panel is used with hardware capable of scaling. Another behaviour
1780 would be to accept any input mode and adjust it to the closest mode
1781 supported by the hardware (FIXME: This needs to be clarified).
1782 </para>
1783 </listitem>
1784 <listitem>
1785 <synopsis>int (*mode_set_base)(struct drm_crtc *crtc, int x, int y,
1786 struct drm_framebuffer *old_fb)</synopsis>
1787 <para>
1788 Move the CRTC on the current frame buffer (stored in
1789 <literal>crtc-&gt;fb</literal>) to position (x,y). Any of the frame
1790 buffer, x position or y position may have been modified.
1791 </para>
1792 <para>
1793 This helper operation is optional. If not provided, the
1794 <function>drm_crtc_helper_set_config</function> function will fall
1795 back to the <methodname>mode_set</methodname> helper operation.
1796 </para>
1797 <note><para>
1798 FIXME: Why are x and y passed as arguments, as they can be accessed
1799 through <literal>crtc-&gt;x</literal> and
1800 <literal>crtc-&gt;y</literal>?
1801 </para></note>
1802 </listitem>
1803 <listitem>
1804 <synopsis>void (*prepare)(struct drm_crtc *crtc);</synopsis>
1805 <para>
1806 Prepare the CRTC for mode setting. This operation is called after
1807 validating the requested mode. Drivers use it to perform
1808 device-specific operations required before setting the new mode.
1809 </para>
1810 </listitem>
1811 <listitem>
1812 <synopsis>int (*mode_set)(struct drm_crtc *crtc, struct drm_display_mode *mode,
1813 struct drm_display_mode *adjusted_mode, int x, int y,
1814 struct drm_framebuffer *old_fb);</synopsis>
1815 <para>
1816 Set a new mode, position and frame buffer. Depending on the device
1817 requirements, the mode can be stored internally by the driver and
1818 applied in the <methodname>commit</methodname> operation, or
1819 programmed to the hardware immediately.
1820 </para>
1821 <para>
1822 The <methodname>mode_set</methodname> operation returns 0 on success
1823 or a negative error code if an error occurs.
1824 </para>
1825 </listitem>
1826 <listitem>
1827 <synopsis>void (*commit)(struct drm_crtc *crtc);</synopsis>
1828 <para>
1829 Commit a mode. This operation is called after setting the new mode.
1830 Upon return the device must use the new mode and be fully
1831 operational.
1832 </para>
1833 </listitem>
1834 </itemizedlist>
1835 </sect2>
1836 <sect2>
1837 <title>Encoder Helper Operations</title>
1838 <itemizedlist>
1839 <listitem>
1840 <synopsis>bool (*mode_fixup)(struct drm_encoder *encoder,
1841 const struct drm_display_mode *mode,
1842 struct drm_display_mode *adjusted_mode);</synopsis>
1843 <note><para>
1844 FIXME: The mode argument be const, but the i915 driver modifies
1845 mode-&gt;clock in <function>intel_dp_mode_fixup</function>.
1846 </para></note>
1847 <para>
1848 Let encoders adjust the requested mode or reject it completely. This
1849 operation returns true if the mode is accepted (possibly after being
1850 adjusted) or false if it is rejected. See the
1851 <link linkend="drm-helper-crtc-mode-fixup">mode_fixup CRTC helper
1852 operation</link> for an explanation of the allowed adjustments.
1853 </para>
1854 </listitem>
1855 <listitem>
1856 <synopsis>void (*prepare)(struct drm_encoder *encoder);</synopsis>
1857 <para>
1858 Prepare the encoder for mode setting. This operation is called after
1859 validating the requested mode. Drivers use it to perform
1860 device-specific operations required before setting the new mode.
1861 </para>
1862 </listitem>
1863 <listitem>
1864 <synopsis>void (*mode_set)(struct drm_encoder *encoder,
1865 struct drm_display_mode *mode,
1866 struct drm_display_mode *adjusted_mode);</synopsis>
1867 <para>
1868 Set a new mode. Depending on the device requirements, the mode can
1869 be stored internally by the driver and applied in the
1870 <methodname>commit</methodname> operation, or programmed to the
1871 hardware immediately.
1872 </para>
1873 </listitem>
1874 <listitem>
1875 <synopsis>void (*commit)(struct drm_encoder *encoder);</synopsis>
1876 <para>
1877 Commit a mode. This operation is called after setting the new mode.
1878 Upon return the device must use the new mode and be fully
1879 operational.
1880 </para>
1881 </listitem>
1882 </itemizedlist>
1883 </sect2>
1884 <sect2>
1885 <title>Connector Helper Operations</title>
1886 <itemizedlist>
1887 <listitem>
1888 <synopsis>struct drm_encoder *(*best_encoder)(struct drm_connector *connector);</synopsis>
1889 <para>
1890 Return a pointer to the best encoder for the connecter. Device that
1891 map connectors to encoders 1:1 simply return the pointer to the
1892 associated encoder. This operation is mandatory.
1893 </para>
1894 </listitem>
1895 <listitem>
1896 <synopsis>int (*get_modes)(struct drm_connector *connector);</synopsis>
1897 <para>
1898 Fill the connector's <structfield>probed_modes</structfield> list
1899 by parsing EDID data with <function>drm_add_edid_modes</function> or
1900 calling <function>drm_mode_probed_add</function> directly for every
1901 supported mode and return the number of modes it has detected. This
1902 operation is mandatory.
1903 </para>
1904 <para>
1905 When adding modes manually the driver creates each mode with a call to
1906 <function>drm_mode_create</function> and must fill the following fields.
1907 <itemizedlist>
1908 <listitem>
1909 <synopsis>__u32 type;</synopsis>
1910 <para>
1911 Mode type bitmask, a combination of
1912 <variablelist>
1913 <varlistentry>
1914 <term>DRM_MODE_TYPE_BUILTIN</term>
1915 <listitem><para>not used?</para></listitem>
1916 </varlistentry>
1917 <varlistentry>
1918 <term>DRM_MODE_TYPE_CLOCK_C</term>
1919 <listitem><para>not used?</para></listitem>
1920 </varlistentry>
1921 <varlistentry>
1922 <term>DRM_MODE_TYPE_CRTC_C</term>
1923 <listitem><para>not used?</para></listitem>
1924 </varlistentry>
1925 <varlistentry>
1926 <term>
1927 DRM_MODE_TYPE_PREFERRED - The preferred mode for the connector
1928 </term>
1929 <listitem>
1930 <para>not used?</para>
1931 </listitem>
1932 </varlistentry>
1933 <varlistentry>
1934 <term>DRM_MODE_TYPE_DEFAULT</term>
1935 <listitem><para>not used?</para></listitem>
1936 </varlistentry>
1937 <varlistentry>
1938 <term>DRM_MODE_TYPE_USERDEF</term>
1939 <listitem><para>not used?</para></listitem>
1940 </varlistentry>
1941 <varlistentry>
1942 <term>DRM_MODE_TYPE_DRIVER</term>
1943 <listitem>
1944 <para>
1945 The mode has been created by the driver (as opposed to
1946 to user-created modes).
1947 </para>
1948 </listitem>
1949 </varlistentry>
1950 </variablelist>
1951 Drivers must set the DRM_MODE_TYPE_DRIVER bit for all modes they
1952 create, and set the DRM_MODE_TYPE_PREFERRED bit for the preferred
1953 mode.
1954 </para>
1955 </listitem>
1956 <listitem>
1957 <synopsis>__u32 clock;</synopsis>
1958 <para>Pixel clock frequency in kHz unit</para>
1959 </listitem>
1960 <listitem>
1961 <synopsis>__u16 hdisplay, hsync_start, hsync_end, htotal;
1962 __u16 vdisplay, vsync_start, vsync_end, vtotal;</synopsis>
1963 <para>Horizontal and vertical timing information</para>
1964 <screen><![CDATA[
1965 Active Front Sync Back
1966 Region Porch Porch
1967 <-----------------------><----------------><-------------><-------------->
1968
1969 //////////////////////|
1970 ////////////////////// |
1971 ////////////////////// |.................. ................
1972 _______________
1973
1974 <----- [hv]display ----->
1975 <------------- [hv]sync_start ------------>
1976 <--------------------- [hv]sync_end --------------------->
1977 <-------------------------------- [hv]total ----------------------------->
1978]]></screen>
1979 </listitem>
1980 <listitem>
1981 <synopsis>__u16 hskew;
1982 __u16 vscan;</synopsis>
1983 <para>Unknown</para>
1984 </listitem>
1985 <listitem>
1986 <synopsis>__u32 flags;</synopsis>
1987 <para>
1988 Mode flags, a combination of
1989 <variablelist>
1990 <varlistentry>
1991 <term>DRM_MODE_FLAG_PHSYNC</term>
1992 <listitem><para>
1993 Horizontal sync is active high
1994 </para></listitem>
1995 </varlistentry>
1996 <varlistentry>
1997 <term>DRM_MODE_FLAG_NHSYNC</term>
1998 <listitem><para>
1999 Horizontal sync is active low
2000 </para></listitem>
2001 </varlistentry>
2002 <varlistentry>
2003 <term>DRM_MODE_FLAG_PVSYNC</term>
2004 <listitem><para>
2005 Vertical sync is active high
2006 </para></listitem>
2007 </varlistentry>
2008 <varlistentry>
2009 <term>DRM_MODE_FLAG_NVSYNC</term>
2010 <listitem><para>
2011 Vertical sync is active low
2012 </para></listitem>
2013 </varlistentry>
2014 <varlistentry>
2015 <term>DRM_MODE_FLAG_INTERLACE</term>
2016 <listitem><para>
2017 Mode is interlaced
2018 </para></listitem>
2019 </varlistentry>
2020 <varlistentry>
2021 <term>DRM_MODE_FLAG_DBLSCAN</term>
2022 <listitem><para>
2023 Mode uses doublescan
2024 </para></listitem>
2025 </varlistentry>
2026 <varlistentry>
2027 <term>DRM_MODE_FLAG_CSYNC</term>
2028 <listitem><para>
2029 Mode uses composite sync
2030 </para></listitem>
2031 </varlistentry>
2032 <varlistentry>
2033 <term>DRM_MODE_FLAG_PCSYNC</term>
2034 <listitem><para>
2035 Composite sync is active high
2036 </para></listitem>
2037 </varlistentry>
2038 <varlistentry>
2039 <term>DRM_MODE_FLAG_NCSYNC</term>
2040 <listitem><para>
2041 Composite sync is active low
2042 </para></listitem>
2043 </varlistentry>
2044 <varlistentry>
2045 <term>DRM_MODE_FLAG_HSKEW</term>
2046 <listitem><para>
2047 hskew provided (not used?)
2048 </para></listitem>
2049 </varlistentry>
2050 <varlistentry>
2051 <term>DRM_MODE_FLAG_BCAST</term>
2052 <listitem><para>
2053 not used?
2054 </para></listitem>
2055 </varlistentry>
2056 <varlistentry>
2057 <term>DRM_MODE_FLAG_PIXMUX</term>
2058 <listitem><para>
2059 not used?
2060 </para></listitem>
2061 </varlistentry>
2062 <varlistentry>
2063 <term>DRM_MODE_FLAG_DBLCLK</term>
2064 <listitem><para>
2065 not used?
2066 </para></listitem>
2067 </varlistentry>
2068 <varlistentry>
2069 <term>DRM_MODE_FLAG_CLKDIV2</term>
2070 <listitem><para>
2071 ?
2072 </para></listitem>
2073 </varlistentry>
2074 </variablelist>
2075 </para>
2076 <para>
2077 Note that modes marked with the INTERLACE or DBLSCAN flags will be
2078 filtered out by
2079 <function>drm_helper_probe_single_connector_modes</function> if
2080 the connector's <structfield>interlace_allowed</structfield> or
2081 <structfield>doublescan_allowed</structfield> field is set to 0.
2082 </para>
2083 </listitem>
2084 <listitem>
2085 <synopsis>char name[DRM_DISPLAY_MODE_LEN];</synopsis>
2086 <para>
2087 Mode name. The driver must call
2088 <function>drm_mode_set_name</function> to fill the mode name from
2089 <structfield>hdisplay</structfield>,
2090 <structfield>vdisplay</structfield> and interlace flag after
2091 filling the corresponding fields.
2092 </para>
2093 </listitem>
2094 </itemizedlist>
2095 </para>
2096 <para>
2097 The <structfield>vrefresh</structfield> value is computed by
2098 <function>drm_helper_probe_single_connector_modes</function>.
2099 </para>
2100 <para>
2101 When parsing EDID data, <function>drm_add_edid_modes</function> fill the
2102 connector <structfield>display_info</structfield>
2103 <structfield>width_mm</structfield> and
2104 <structfield>height_mm</structfield> fields. When creating modes
2105 manually the <methodname>get_modes</methodname> helper operation must
2106 set the <structfield>display_info</structfield>
2107 <structfield>width_mm</structfield> and
2108 <structfield>height_mm</structfield> fields if they haven't been set
2109 already (for instance at initilization time when a fixed-size panel is
2110 attached to the connector). The mode <structfield>width_mm</structfield>
2111 and <structfield>height_mm</structfield> fields are only used internally
2112 during EDID parsing and should not be set when creating modes manually.
2113 </para>
2114 </listitem>
2115 <listitem>
2116 <synopsis>int (*mode_valid)(struct drm_connector *connector,
2117 struct drm_display_mode *mode);</synopsis>
2118 <para>
2119 Verify whether a mode is valid for the connector. Return MODE_OK for
2120 supported modes and one of the enum drm_mode_status values (MODE_*)
2121 for unsupported modes. This operation is mandatory.
2122 </para>
2123 <para>
2124 As the mode rejection reason is currently not used beside for
2125 immediately removing the unsupported mode, an implementation can
2126 return MODE_BAD regardless of the exact reason why the mode is not
2127 valid.
2128 </para>
2129 <note><para>
2130 Note that the <methodname>mode_valid</methodname> helper operation is
2131 only called for modes detected by the device, and
2132 <emphasis>not</emphasis> for modes set by the user through the CRTC
2133 <methodname>set_config</methodname> operation.
2134 </para></note>
2135 </listitem>
2136 </itemizedlist>
2137 </sect2>
Daniel Vetter0d4ed4c2012-11-01 14:45:16 +01002138 <sect2>
2139 <title>Modeset Helper Functions Reference</title>
2140!Edrivers/gpu/drm/drm_crtc_helper.c
2141 </sect2>
Daniel Vetterd0ddc0332012-11-01 14:45:17 +01002142 <sect2>
2143 <title>fbdev Helper Functions Reference</title>
2144!Pdrivers/gpu/drm/drm_fb_helper.c fbdev helpers
2145!Edrivers/gpu/drm/drm_fb_helper.c
Daniel Vetter207fd322013-01-20 22:13:14 +01002146!Iinclude/drm/drm_fb_helper.h
Daniel Vetterd0ddc0332012-11-01 14:45:17 +01002147 </sect2>
Daniel Vetter28164fd2012-11-01 14:45:18 +01002148 <sect2>
2149 <title>Display Port Helper Functions Reference</title>
2150!Pdrivers/gpu/drm/drm_dp_helper.c dp helpers
2151!Iinclude/drm/drm_dp_helper.h
2152!Edrivers/gpu/drm/drm_dp_helper.c
2153 </sect2>
Thierry Reding5e308592013-01-14 09:00:31 +01002154 <sect2>
2155 <title>EDID Helper Functions Reference</title>
2156!Edrivers/gpu/drm/drm_edid.c
2157 </sect2>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02002158 </sect1>
2159
2160 <!-- Internals: vertical blanking -->
2161
2162 <sect1 id="drm-vertical-blank">
2163 <title>Vertical Blanking</title>
2164 <para>
2165 Vertical blanking plays a major role in graphics rendering. To achieve
2166 tear-free display, users must synchronize page flips and/or rendering to
2167 vertical blanking. The DRM API offers ioctls to perform page flips
2168 synchronized to vertical blanking and wait for vertical blanking.
2169 </para>
2170 <para>
2171 The DRM core handles most of the vertical blanking management logic, which
2172 involves filtering out spurious interrupts, keeping race-free blanking
2173 counters, coping with counter wrap-around and resets and keeping use
2174 counts. It relies on the driver to generate vertical blanking interrupts
2175 and optionally provide a hardware vertical blanking counter. Drivers must
2176 implement the following operations.
2177 </para>
2178 <itemizedlist>
2179 <listitem>
2180 <synopsis>int (*enable_vblank) (struct drm_device *dev, int crtc);
2181void (*disable_vblank) (struct drm_device *dev, int crtc);</synopsis>
2182 <para>
2183 Enable or disable vertical blanking interrupts for the given CRTC.
2184 </para>
2185 </listitem>
2186 <listitem>
2187 <synopsis>u32 (*get_vblank_counter) (struct drm_device *dev, int crtc);</synopsis>
2188 <para>
2189 Retrieve the value of the vertical blanking counter for the given
2190 CRTC. If the hardware maintains a vertical blanking counter its value
2191 should be returned. Otherwise drivers can use the
2192 <function>drm_vblank_count</function> helper function to handle this
2193 operation.
2194 </para>
2195 </listitem>
2196 </itemizedlist>
2197 <para>
2198 Drivers must initialize the vertical blanking handling core with a call to
2199 <function>drm_vblank_init</function> in their
2200 <methodname>load</methodname> operation. The function will set the struct
2201 <structname>drm_device</structname>
2202 <structfield>vblank_disable_allowed</structfield> field to 0. This will
2203 keep vertical blanking interrupts enabled permanently until the first mode
2204 set operation, where <structfield>vblank_disable_allowed</structfield> is
2205 set to 1. The reason behind this is not clear. Drivers can set the field
2206 to 1 after <function>calling drm_vblank_init</function> to make vertical
2207 blanking interrupts dynamically managed from the beginning.
2208 </para>
2209 <para>
2210 Vertical blanking interrupts can be enabled by the DRM core or by drivers
2211 themselves (for instance to handle page flipping operations). The DRM core
2212 maintains a vertical blanking use count to ensure that the interrupts are
2213 not disabled while a user still needs them. To increment the use count,
2214 drivers call <function>drm_vblank_get</function>. Upon return vertical
2215 blanking interrupts are guaranteed to be enabled.
2216 </para>
2217 <para>
2218 To decrement the use count drivers call
2219 <function>drm_vblank_put</function>. Only when the use count drops to zero
2220 will the DRM core disable the vertical blanking interrupts after a delay
2221 by scheduling a timer. The delay is accessible through the vblankoffdelay
2222 module parameter or the <varname>drm_vblank_offdelay</varname> global
2223 variable and expressed in milliseconds. Its default value is 5000 ms.
2224 </para>
2225 <para>
2226 When a vertical blanking interrupt occurs drivers only need to call the
2227 <function>drm_handle_vblank</function> function to account for the
2228 interrupt.
2229 </para>
2230 <para>
2231 Resources allocated by <function>drm_vblank_init</function> must be freed
2232 with a call to <function>drm_vblank_cleanup</function> in the driver
2233 <methodname>unload</methodname> operation handler.
2234 </para>
2235 </sect1>
2236
2237 <!-- Internals: open/close, file operations and ioctls -->
2238
2239 <sect1>
2240 <title>Open/Close, File Operations and IOCTLs</title>
2241 <sect2>
2242 <title>Open and Close</title>
2243 <synopsis>int (*firstopen) (struct drm_device *);
2244void (*lastclose) (struct drm_device *);
2245int (*open) (struct drm_device *, struct drm_file *);
2246void (*preclose) (struct drm_device *, struct drm_file *);
2247void (*postclose) (struct drm_device *, struct drm_file *);</synopsis>
2248 <abstract>Open and close handlers. None of those methods are mandatory.
2249 </abstract>
2250 <para>
2251 The <methodname>firstopen</methodname> method is called by the DRM core
2252 when an application opens a device that has no other opened file handle.
2253 Similarly the <methodname>lastclose</methodname> method is called when
2254 the last application holding a file handle opened on the device closes
2255 it. Both methods are mostly used for UMS (User Mode Setting) drivers to
2256 acquire and release device resources which should be done in the
2257 <methodname>load</methodname> and <methodname>unload</methodname>
2258 methods for KMS drivers.
2259 </para>
2260 <para>
2261 Note that the <methodname>lastclose</methodname> method is also called
2262 at module unload time or, for hot-pluggable devices, when the device is
2263 unplugged. The <methodname>firstopen</methodname> and
2264 <methodname>lastclose</methodname> calls can thus be unbalanced.
2265 </para>
2266 <para>
2267 The <methodname>open</methodname> method is called every time the device
2268 is opened by an application. Drivers can allocate per-file private data
2269 in this method and store them in the struct
2270 <structname>drm_file</structname> <structfield>driver_priv</structfield>
2271 field. Note that the <methodname>open</methodname> method is called
2272 before <methodname>firstopen</methodname>.
2273 </para>
2274 <para>
2275 The close operation is split into <methodname>preclose</methodname> and
2276 <methodname>postclose</methodname> methods. Drivers must stop and
2277 cleanup all per-file operations in the <methodname>preclose</methodname>
2278 method. For instance pending vertical blanking and page flip events must
2279 be cancelled. No per-file operation is allowed on the file handle after
2280 returning from the <methodname>preclose</methodname> method.
2281 </para>
2282 <para>
2283 Finally the <methodname>postclose</methodname> method is called as the
2284 last step of the close operation, right before calling the
2285 <methodname>lastclose</methodname> method if no other open file handle
2286 exists for the device. Drivers that have allocated per-file private data
2287 in the <methodname>open</methodname> method should free it here.
2288 </para>
2289 <para>
2290 The <methodname>lastclose</methodname> method should restore CRTC and
2291 plane properties to default value, so that a subsequent open of the
2292 device will not inherit state from the previous user.
2293 </para>
2294 </sect2>
2295 <sect2>
2296 <title>File Operations</title>
2297 <synopsis>const struct file_operations *fops</synopsis>
2298 <abstract>File operations for the DRM device node.</abstract>
2299 <para>
2300 Drivers must define the file operations structure that forms the DRM
2301 userspace API entry point, even though most of those operations are
2302 implemented in the DRM core. The <methodname>open</methodname>,
2303 <methodname>release</methodname> and <methodname>ioctl</methodname>
2304 operations are handled by
2305 <programlisting>
2306 .owner = THIS_MODULE,
2307 .open = drm_open,
2308 .release = drm_release,
2309 .unlocked_ioctl = drm_ioctl,
2310 #ifdef CONFIG_COMPAT
2311 .compat_ioctl = drm_compat_ioctl,
2312 #endif
2313 </programlisting>
2314 </para>
2315 <para>
2316 Drivers that implement private ioctls that requires 32/64bit
2317 compatibility support must provide their own
2318 <methodname>compat_ioctl</methodname> handler that processes private
2319 ioctls and calls <function>drm_compat_ioctl</function> for core ioctls.
2320 </para>
2321 <para>
2322 The <methodname>read</methodname> and <methodname>poll</methodname>
2323 operations provide support for reading DRM events and polling them. They
2324 are implemented by
2325 <programlisting>
2326 .poll = drm_poll,
2327 .read = drm_read,
2328 .fasync = drm_fasync,
2329 .llseek = no_llseek,
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002330 </programlisting>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02002331 </para>
2332 <para>
2333 The memory mapping implementation varies depending on how the driver
2334 manages memory. Pre-GEM drivers will use <function>drm_mmap</function>,
2335 while GEM-aware drivers will use <function>drm_gem_mmap</function>. See
2336 <xref linkend="drm-gem"/>.
2337 <programlisting>
2338 .mmap = drm_gem_mmap,
2339 </programlisting>
2340 </para>
2341 <para>
2342 No other file operation is supported by the DRM API.
2343 </para>
2344 </sect2>
2345 <sect2>
2346 <title>IOCTLs</title>
2347 <synopsis>struct drm_ioctl_desc *ioctls;
2348int num_ioctls;</synopsis>
2349 <abstract>Driver-specific ioctls descriptors table.</abstract>
2350 <para>
2351 Driver-specific ioctls numbers start at DRM_COMMAND_BASE. The ioctls
2352 descriptors table is indexed by the ioctl number offset from the base
2353 value. Drivers can use the DRM_IOCTL_DEF_DRV() macro to initialize the
2354 table entries.
2355 </para>
2356 <para>
2357 <programlisting>DRM_IOCTL_DEF_DRV(ioctl, func, flags)</programlisting>
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002358 <para>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02002359 <parameter>ioctl</parameter> is the ioctl name. Drivers must define
2360 the DRM_##ioctl and DRM_IOCTL_##ioctl macros to the ioctl number
2361 offset from DRM_COMMAND_BASE and the ioctl number respectively. The
2362 first macro is private to the device while the second must be exposed
2363 to userspace in a public header.
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002364 </para>
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002365 <para>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02002366 <parameter>func</parameter> is a pointer to the ioctl handler function
2367 compatible with the <type>drm_ioctl_t</type> type.
2368 <programlisting>typedef int drm_ioctl_t(struct drm_device *dev, void *data,
2369 struct drm_file *file_priv);</programlisting>
2370 </para>
2371 <para>
2372 <parameter>flags</parameter> is a bitmask combination of the following
2373 values. It restricts how the ioctl is allowed to be called.
Michael Witten65ffef52011-08-25 20:55:58 +00002374 <itemizedlist>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02002375 <listitem><para>
2376 DRM_AUTH - Only authenticated callers allowed
2377 </para></listitem>
2378 <listitem><para>
2379 DRM_MASTER - The ioctl can only be called on the master file
2380 handle
2381 </para></listitem>
2382 <listitem><para>
2383 DRM_ROOT_ONLY - Only callers with the SYSADMIN capability allowed
2384 </para></listitem>
2385 <listitem><para>
2386 DRM_CONTROL_ALLOW - The ioctl can only be called on a control
2387 device
2388 </para></listitem>
2389 <listitem><para>
2390 DRM_UNLOCKED - The ioctl handler will be called without locking
2391 the DRM global mutex
2392 </para></listitem>
Michael Witten65ffef52011-08-25 20:55:58 +00002393 </itemizedlist>
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002394 </para>
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002395 </para>
2396 </sect2>
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002397 </sect1>
2398
2399 <sect1>
2400 <title>Command submission &amp; fencing</title>
2401 <para>
Michael Wittena5294e02011-08-29 18:05:52 +00002402 This should cover a few device-specific command submission
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002403 implementations.
2404 </para>
2405 </sect1>
2406
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02002407 <!-- Internals: suspend/resume -->
2408
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002409 <sect1>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02002410 <title>Suspend/Resume</title>
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002411 <para>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02002412 The DRM core provides some suspend/resume code, but drivers wanting full
2413 suspend/resume support should provide save() and restore() functions.
2414 These are called at suspend, hibernate, or resume time, and should perform
2415 any state save or restore required by your device across suspend or
2416 hibernate states.
2417 </para>
2418 <synopsis>int (*suspend) (struct drm_device *, pm_message_t state);
2419int (*resume) (struct drm_device *);</synopsis>
2420 <para>
2421 Those are legacy suspend and resume methods. New driver should use the
2422 power management interface provided by their bus type (usually through
2423 the struct <structname>device_driver</structname> dev_pm_ops) and set
2424 these methods to NULL.
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002425 </para>
2426 </sect1>
2427
2428 <sect1>
2429 <title>DMA services</title>
2430 <para>
2431 This should cover how DMA mapping etc. is supported by the core.
2432 These functions are deprecated and should not be used.
2433 </para>
2434 </sect1>
2435 </chapter>
2436
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02002437<!-- TODO
2438
2439- Add a glossary
2440- Document the struct_mutex catch-all lock
2441- Document connector properties
2442
2443- Why is the load method optional?
2444- What are drivers supposed to set the initial display state to, and how?
2445 Connector's DPMS states are not initialized and are thus equal to
2446 DRM_MODE_DPMS_ON. The fbcon compatibility layer calls
2447 drm_helper_disable_unused_functions(), which disables unused encoders and
2448 CRTCs, but doesn't touch the connectors' DPMS state, and
2449 drm_helper_connector_dpms() in reaction to fbdev blanking events. Do drivers
2450 that don't implement (or just don't use) fbcon compatibility need to call
2451 those functions themselves?
2452- KMS drivers must call drm_vblank_pre_modeset() and drm_vblank_post_modeset()
2453 around mode setting. Should this be done in the DRM core?
2454- vblank_disable_allowed is set to 1 in the first drm_vblank_post_modeset()
2455 call and never set back to 0. It seems to be safe to permanently set it to 1
2456 in drm_vblank_init() for KMS driver, and it might be safe for UMS drivers as
2457 well. This should be investigated.
2458- crtc and connector .save and .restore operations are only used internally in
2459 drivers, should they be removed from the core?
2460- encoder mid-layer .save and .restore operations are only used internally in
2461 drivers, should they be removed from the core?
2462- encoder mid-layer .detect operation is only used internally in drivers,
2463 should it be removed from the core?
2464-->
2465
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002466 <!-- External interfaces -->
2467
2468 <chapter id="drmExternals">
2469 <title>Userland interfaces</title>
2470 <para>
2471 The DRM core exports several interfaces to applications,
2472 generally intended to be used through corresponding libdrm
Michael Wittena5294e02011-08-29 18:05:52 +00002473 wrapper functions. In addition, drivers export device-specific
Michael Witten7f0925a2011-08-29 18:07:13 +00002474 interfaces for use by userspace drivers &amp; device-aware
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002475 applications through ioctls and sysfs files.
2476 </para>
2477 <para>
2478 External interfaces include: memory mapping, context management,
2479 DMA operations, AGP management, vblank control, fence
2480 management, memory management, and output management.
2481 </para>
2482 <para>
Michael Wittenbcd3cfc2011-08-29 19:29:16 +00002483 Cover generic ioctls and sysfs layout here. We only need high-level
2484 info, since man pages should cover the rest.
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002485 </para>
Laurent Pinchart9cad9c92012-07-13 00:57:26 +02002486
2487 <!-- External: vblank handling -->
2488
2489 <sect1>
2490 <title>VBlank event handling</title>
2491 <para>
2492 The DRM core exposes two vertical blank related ioctls:
2493 <variablelist>
2494 <varlistentry>
2495 <term>DRM_IOCTL_WAIT_VBLANK</term>
2496 <listitem>
2497 <para>
2498 This takes a struct drm_wait_vblank structure as its argument,
2499 and it is used to block or request a signal when a specified
2500 vblank event occurs.
2501 </para>
2502 </listitem>
2503 </varlistentry>
2504 <varlistentry>
2505 <term>DRM_IOCTL_MODESET_CTL</term>
2506 <listitem>
2507 <para>
2508 This should be called by application level drivers before and
2509 after mode setting, since on many devices the vertical blank
2510 counter is reset at that time. Internally, the DRM snapshots
2511 the last vblank count when the ioctl is called with the
2512 _DRM_PRE_MODESET command, so that the counter won't go backwards
2513 (which is dealt with when _DRM_POST_MODESET is used).
2514 </para>
2515 </listitem>
2516 </varlistentry>
2517 </variablelist>
2518<!--!Edrivers/char/drm/drm_irq.c-->
2519 </para>
2520 </sect1>
2521
Jesse Barnes2d2ef822009-10-26 13:06:31 -07002522 </chapter>
2523
2524 <!-- API reference -->
2525
2526 <appendix id="drmDriverApi">
2527 <title>DRM Driver API</title>
2528 <para>
2529 Include auto-generated API reference here (need to reference it
2530 from paragraphs above too).
2531 </para>
2532 </appendix>
2533
2534</book>