1DRM(7)                     Direct Rendering Manager                     DRM(7)
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NAME

6       drm - Direct Rendering Manager
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SYNOPSIS

9       #include <xf86drm.h>
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DESCRIPTION

12       The  Direct  Rendering  Manager (DRM) is a framework to manage Graphics
13       Processing Units (GPUs). It is designed to support the needs of complex
14       graphics devices, usually containing programmable pipelines well suited
15       to 3D graphics acceleration. Furthermore, it is responsible for  memory
16       management,  interrupt  handling and DMA to provide a uniform interface
17       to applications.
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19       In earlier days, the kernel framework was solely used  to  provide  raw
20       hardware  access to privileged user-space processes which implement all
21       the hardware abstraction layers. But more and  more  tasks  were  moved
22       into the kernel. All these interfaces are based on ioctl(2) commands on
23       the DRM character device. The  libdrm  library  provides  wrappers  for
24       these system-calls and many helpers to simplify the API.
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26       When  a GPU is detected, the DRM system loads a driver for the detected
27       hardware type. Each connected GPU is then presented to user-space via a
28       character-device that is usually available as /dev/dri/card0 and can be
29       accessed with open(2) and close(2). However, it still  depends  on  the
30       graphics  driver which interfaces are available on these devices. If an
31       interface is not available, the syscalls will fail with EINVAL.
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33   Authentication
34       All DRM devices provide authentication mechanisms. Only a DRM master is
35       allowed  to perform mode-setting or modify core state and only one user
36       can be DRM master at a time. See drmSetMaster(3) for information on how
37       to  become DRM master and what the limitations are. Other DRM users can
38       be authenticated to the DRM-Master via drmAuthMagic(3) so they can per‐
39       form buffer allocations and rendering.
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41   Mode-Setting
42       Managing connected monitors and displays and changing the current modes
43       is called Mode-Setting. This is restricted to the current  DRM  master.
44       Historically,  this  was implemented in user-space, but new DRM drivers
45       implement a kernel interface to perform mode-setting called Kernel Mode
46       Setting (KMS). If your hardware-driver supports it, you can use the KMS
47       API provided by DRM. This includes allocating  framebuffers,  selecting
48       modes and managing CRTCs and encoders. See drm-kms(7) for more.
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50   Memory Management
51       The most sophisticated tasks for GPUs today is managing memory objects.
52       Textures, framebuffers, command-buffers and all other kinds of commands
53       for  the  GPU have to be stored in memory. The DRM driver takes care of
54       managing all memory objects, flushing caches, synchronizing access  and
55       providing  CPU  access to GPU memory. All memory management is hardware
56       driver dependent. However, two generic frameworks  are  available  that
57       are  used  by most DRM drivers. These are the Translation Table Manager
58       (TTM) and the Graphics Execution Manager (GEM).  They  provide  generic
59       APIs  to  create,  destroy and access buffers from user-space. However,
60       there are still many differences between the drivers  so  driver-depen‐
61       dent  code is still needed. Many helpers are provided in libgbm (Graph‐
62       ics Buffer Manager) from the Mesa project. For more information on  DRM
63       memory management, see drm-memory(7).
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REPORTING BUGS

66       Bugs      in      this     manual     should     be     reported     to
67       https://gitlab.freedesktop.org/mesa/drm/-/issues.
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SEE ALSO

70       drm-kms(7), drm-memory(7), drmSetMaster(3), drmAuthMagic(3),  drmAvail‐
71       able(3), drmOpen(3)
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76                                September 2012                          DRM(7)
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