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DRM(7)			   Direct Rendering Manager			DRM(7)

       drm - Direct Rendering Manager

       #include	<xf86drm.h>

       The Direct Rendering Manager (DRM) is a framework to manage Graphics
       Processing Units	(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.

       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 ioctl(2) commands on
       the DRM character device. The libdrm library provides wrappers for
       these system-calls and many helpers to simplify the API.

       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 /dev/dri/card0 and	can be
       accessed	with open(2) and close(2). 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 EINVAL.

       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	drmSetMaster(3)	for information	on how
       to become DRM-Master and	what the limitations are. Other	DRM users can
       be authenticated	to the DRM-Master via drmAuthMagic(3) so they can
       perform buffer allocations and rendering.

       Managing	connected monitors and displays	and changing the current modes
       is called Mode-Setting. 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 Kernel Mode
       Setting (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 drm-kms(7) for more.

   Memory Management
       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 Translation Table Manager
       (TTM) and the Graphics Execution	Manager	(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 libgbm (Graphics
       Buffer Manager) from the	mesa-project. For more information on DRM
       memory-management, see drm-memory(7).

       Bugs in this manual should be reported to
       under the "DRI" product,	component "libdrm"

       drm-kms(7), drm-memory(7), drmSetMaster(3), drmAuthMagic(3),
       drmAvailable(3),	drmOpen(3)

libdrm				September 2012				DRM(7)


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