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
39       perform 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-depedent
61       code is still needed. Many helpers are provided in libgbm (Graphics
62       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://bugs.freedesktop.org/enter_bug.cgi?product=DRI&component=libdrm
68       under the "DRI" product, component "libdrm"
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SEE ALSO

71       drm-kms(7), drm-memory(7), drmSetMaster(3), drmAuthMagic(3),
72       drmAvailable(3), drmOpen(3)
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76libdrm                          September 2012                          DRM(7)
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