"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

  Written 2012 by David Herrmann <dh.herrmann@googlemail.com>

  Dedicated to the Public Domain

-->

<refentry id="drm">

  <refentryinfo>

    <title>Direct Rendering Manager</title>

    <productname>libdrm</productname>

    <date>September 2012</date>

    <authorgroup>

      <author>

        <contrib>Developer</contrib>

        <firstname>David</firstname>

        <surname>Herrmann</surname>

        <email>dh.herrmann@googlemail.com</email>

      </author>

    </authorgroup>

  </refentryinfo>

  <refmeta>

    <refentrytitle>drm</refentrytitle>

    <manvolnum>7</manvolnum>

  </refmeta>

  <refnamediv>

    <refname>drm</refname>

    <refpurpose>Direct Rendering Manager</refpurpose>

  </refnamediv>

  <refsynopsisdiv>

    <funcsynopsis>

      <funcsynopsisinfo>#include <xf86drm.h></funcsynopsisinfo>

    </funcsynopsis>

  </refsynopsisdiv>

  <refsect1>

    <title>Description</title>

    <para>The <emphasis>Direct Rendering Manager</emphasis> (DRM) is a framework

          to manage <emphasis>Graphics Processing Units</emphasis> (GPUs). It is

          designed to support the needs of complex graphics devices, usually

          containing programmable pipelines well suited to 3D graphics

          acceleration. Furthermore, it is responsible for memory management,

          interrupt handling and DMA to provide a uniform interface to

          applications.</para>

    <para>In earlier days, the kernel framework was solely used to provide raw

          hardware access to privileged user-space processes which implement

          all the hardware abstraction layers. But more and more tasks were

          moved into the kernel. All these interfaces are based on

          <citerefentry><refentrytitle>ioctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>

          commands on the DRM character device. The <emphasis>libdrm</emphasis>

          library provides wrappers for these system-calls and many helpers to

          simplify the API.</para>

    <para>When a GPU is detected, the DRM system loads a driver for the detected

          hardware type. Each connected GPU is then presented to user-space via

          a character-device that is usually available as

          <filename>/dev/dri/card0</filename> and can be accessed with

          <citerefentry><refentrytitle>open</refentrytitle><manvolnum>2</manvolnum></citerefentry>

          and

          <citerefentry><refentrytitle>close</refentrytitle><manvolnum>2</manvolnum></citerefentry>.

          However, it still depends on the graphics driver which interfaces are

          available on these devices. If an interface is not available, the

          syscalls will fail with <literal>EINVAL</literal>.</para>

    <refsect2>

      <title>Authentication</title>

      <para>All DRM devices provide authentication mechanisms. Only a DRM-Master

            is allowed to perform mode-setting or modify core state and only one

            user can be DRM-Master at a time. See

            <citerefentry><refentrytitle>drmSetMaster</refentrytitle><manvolnum>3</manvolnum></citerefentry>

            for information on how to become DRM-Master and what the limitations

            are. Other DRM users can be authenticated to the DRM-Master via

            <citerefentry><refentrytitle>drmAuthMagic</refentrytitle><manvolnum>3</manvolnum></citerefentry>

            so they can perform buffer allocations and rendering.</para>

    </refsect2>

    <refsect2>

      <title>Mode-Setting</title>

      <para>Managing connected monitors and displays and changing the current

            modes is called <emphasis>Mode-Setting</emphasis>. This is

            restricted to the current DRM-Master. Historically, this was

            implemented in user-space, but new DRM drivers implement a kernel

            interface to perform mode-setting called

            <emphasis>Kernel Mode Setting</emphasis> (KMS). If your

            hardware-driver supports it, you can use the KMS API provided by

            DRM. This includes allocating framebuffers, selecting modes and

            managing CRTCs and encoders. See

            <citerefentry><refentrytitle>drm-kms</refentrytitle><manvolnum>7</manvolnum></citerefentry>

            for more.</para>

    </refsect2>

    <refsect2>

      <title>Memory Management</title>

      <para>The most sophisticated tasks for GPUs today is managing memory

            objects. Textures, framebuffers, command-buffers and all other kinds

            of commands for the GPU have to be stored in memory. The DRM driver

            takes care of managing all memory objects, flushing caches,

            synchronizing access and providing CPU access to GPU memory. All

            memory management is hardware driver dependent. However, two generic

            frameworks are available that are used by most DRM drivers. These

            are the <emphasis>Translation Table Manager</emphasis> (TTM) and the

            <emphasis>Graphics Execution Manager</emphasis> (GEM). They provide

            generic APIs to create, destroy and access buffers from user-space.

            However, there are still many differences between the drivers so

            driver-depedent code is still needed. Many helpers are provided in

            <emphasis>libgbm</emphasis> (Graphics Buffer Manager) from the

            <emphasis>mesa-project</emphasis>. For more information on DRM

            memory-management, see

            <citerefentry><refentrytitle>drm-memory</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>

    </refsect2>

  </refsect1>

  <refsect1>

    <title>Reporting Bugs</title>

    <para>Bugs in this manual should be reported to

      https://gitlab.freedesktop.org/mesa/drm/-/issues</para>

  </refsect1>

  <refsect1>

    <title>See Also</title>

    <para>

      <citerefentry><refentrytitle>drm-kms</refentrytitle><manvolnum>7</manvolnum></citerefentry>,

      <citerefentry><refentrytitle>drm-memory</refentrytitle><manvolnum>7</manvolnum></citerefentry>,

      <citerefentry><refentrytitle>drmSetMaster</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

      <citerefentry><refentrytitle>drmAuthMagic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

      <citerefentry><refentrytitle>drmAvailable</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

      <citerefentry><refentrytitle>drmOpen</refentrytitle><manvolnum>3</manvolnum></citerefentry>

    </para>

  </refsect1>

</refentry>