David Herrmann | 0a766a5 | 2012-09-28 23:44:20 +0200 | [diff] [blame] | 1 | <?xml version='1.0'?> <!--*-nxml-*--> |
| 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" |
| 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
| 4 | |
| 5 | <!-- |
| 6 | Written 2012 by David Herrmann <dh.herrmann@googlemail.com> |
| 7 | Dedicated to the Public Domain |
| 8 | --> |
| 9 | |
| 10 | <refentry id="drm"> |
| 11 | <refentryinfo> |
| 12 | <title>Direct Rendering Manager</title> |
| 13 | <productname>libdrm</productname> |
| 14 | <date>September 2012</date> |
| 15 | <authorgroup> |
| 16 | <author> |
| 17 | <contrib>Developer</contrib> |
| 18 | <firstname>David</firstname> |
| 19 | <surname>Herrmann</surname> |
| 20 | <email>dh.herrmann@googlemail.com</email> |
| 21 | </author> |
| 22 | </authorgroup> |
| 23 | </refentryinfo> |
| 24 | |
| 25 | <refmeta> |
| 26 | <refentrytitle>drm</refentrytitle> |
| 27 | <manvolnum>7</manvolnum> |
| 28 | </refmeta> |
| 29 | |
| 30 | <refnamediv> |
| 31 | <refname>drm</refname> |
| 32 | <refpurpose>Direct Rendering Manager</refpurpose> |
| 33 | </refnamediv> |
| 34 | |
| 35 | <refsynopsisdiv> |
| 36 | <funcsynopsis> |
| 37 | <funcsynopsisinfo>#include <xf86drm.h></funcsynopsisinfo> |
| 38 | </funcsynopsis> |
| 39 | </refsynopsisdiv> |
| 40 | |
| 41 | <refsect1> |
| 42 | <title>Description</title> |
| 43 | <para>The <emphasis>Direct Rendering Manager</emphasis> (DRM) is a framework |
| 44 | to manage <emphasis>Graphics Processing Units</emphasis> (GPUs). It is |
| 45 | designed to support the needs of complex graphics devices, usually |
| 46 | containing programmable pipelines well suited to 3D graphics |
| 47 | acceleration. Furthermore, it is responsible for memory management, |
| 48 | interrupt handling and DMA to provide a uniform interface to |
| 49 | applications.</para> |
| 50 | |
| 51 | <para>In earlier days, the kernel framework was solely used to provide raw |
| 52 | hardware access to priviledged user-space processes which implement |
| 53 | all the hardware abstraction layers. But more and more tasks where |
| 54 | moved into the kernel. All these interfaces are based on |
| 55 | <citerefentry><refentrytitle>ioctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> |
| 56 | commands on the DRM character device. The <emphasis>libdrm</emphasis> |
| 57 | library provides wrappers for these system-calls and many helpers to |
| 58 | simplify the API.</para> |
| 59 | |
| 60 | <para>When a GPU is detected, the DRM system loads a driver for the detected |
| 61 | hardware type. Each connected GPU is then presented to user-space via |
| 62 | a character-device that is usually available as |
| 63 | <filename>/dev/dri/card0</filename> and can be accessed with |
| 64 | <citerefentry><refentrytitle>open</refentrytitle><manvolnum>2</manvolnum></citerefentry> |
| 65 | and |
| 66 | <citerefentry><refentrytitle>close</refentrytitle><manvolnum>2</manvolnum></citerefentry>. |
| 67 | However, it still depends on the grapics driver which interfaces are |
| 68 | available on these devices. If an interface is not available, the |
| 69 | syscalls will fail with <literal>EINVAL</literal>.</para> |
| 70 | |
| 71 | <refsect2> |
| 72 | <title>Authentication</title> |
| 73 | <para>All DRM devices provide authentication mechanisms. Only a DRM-Master |
| 74 | is allowed to perform mode-setting or modify core state and only one |
| 75 | user can be DRM-Master at a time. See |
| 76 | <citerefentry><refentrytitle>drmSetMaster</refentrytitle><manvolnum>3</manvolnum></citerefentry> |
| 77 | for information on how to become DRM-Master and what the limitations |
| 78 | are. Other DRM users can be authenticated to the DRM-Master via |
| 79 | <citerefentry><refentrytitle>drmAuthMagic</refentrytitle><manvolnum>3</manvolnum></citerefentry> |
| 80 | so they can perform buffer allocations and rendering.</para> |
| 81 | </refsect2> |
| 82 | |
| 83 | <refsect2> |
| 84 | <title>Mode-Setting</title> |
| 85 | <para>Managing connected monitors and displays and changing the current |
| 86 | modes is called <emphasis>Mode-Setting</emphasis>. This is |
| 87 | restricted to the current DRM-Master. Historically, this was |
| 88 | implemented in user-space, but new DRM drivers implement a kernel |
| 89 | interface to perform mode-setting called |
| 90 | <emphasis>Kernel Mode Setting</emphasis> (KMS). If your |
| 91 | hardware-driver supports it, you can use the KMS API provided by |
| 92 | DRM. This includes allocating framebuffers, selecting modes and |
| 93 | managing CRTCs and encoders. See |
| 94 | <citerefentry><refentrytitle>drm-kms</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
| 95 | for more.</para> |
| 96 | </refsect2> |
| 97 | |
| 98 | <refsect2> |
| 99 | <title>Memory Management</title> |
| 100 | <para>The most sophisticated tasks for GPUs today is managing memory |
| 101 | objects. Textures, framebuffers, command-buffers and all other kinds |
| 102 | of commands for the GPU have to be stored in memory. The DRM driver |
| 103 | takes care of managing all memory objects, flushing caches, |
| 104 | synchronizing access and providing CPU access to GPU memory. All |
| 105 | memory management is hardware driver dependent. However, two generic |
| 106 | frameworks are available that are used by most DRM drivers. These |
| 107 | are the <emphasis>Translation Table Manager</emphasis> (TTM) and the |
| 108 | <emphasis>Graphics Execution Manager</emphasis> (GEM). They provide |
| 109 | generic APIs to create, destroy and access buffers from user-space. |
| 110 | However, there are still many differences between the drivers so |
| 111 | driver-depedent code is still needed. Many helpers are provided in |
| 112 | <emphasis>libgbm</emphasis> (Graphics Buffer Manager) from the |
| 113 | <emphasis>mesa-project</emphasis>. For more information on DRM |
| 114 | memory-management, see |
| 115 | <citerefentry><refentrytitle>drm-memory</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para> |
| 116 | </refsect2> |
| 117 | </refsect1> |
| 118 | |
| 119 | <refsect1> |
| 120 | <title>Reporting Bugs</title> |
| 121 | <para>Bugs in this manual should be reported to |
| 122 | http://bugs.freedesktop.org under the "Mesa" product, with "Other" or |
| 123 | "libdrm" as the component.</para> |
| 124 | </refsect1> |
| 125 | |
| 126 | <refsect1> |
| 127 | <title>See Also</title> |
| 128 | <para> |
| 129 | <citerefentry><refentrytitle>drm-kms</refentrytitle><manvolnum>7</manvolnum></citerefentry>, |
| 130 | <citerefentry><refentrytitle>drm-memory</refentrytitle><manvolnum>7</manvolnum></citerefentry>, |
| 131 | <citerefentry><refentrytitle>drmSetMaster</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
| 132 | <citerefentry><refentrytitle>drmAuthMagic</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
| 133 | <citerefentry><refentrytitle>drmAvailable</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
| 134 | <citerefentry><refentrytitle>drmOpen</refentrytitle><manvolnum>3</manvolnum></citerefentry> |
| 135 | </para> |
| 136 | </refsect1> |
| 137 | </refentry> |