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DRM(7)                     Direct Rendering Manager                     DRM(7)


NAME

       drm - Direct Rendering Manager


SYNOPSIS

       #include <xf86drm.h>


DESCRIPTION

       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.

   Authentication
       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.

   Mode-Setting
       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-dependent 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).


REPORTING BUGS

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


SEE ALSO

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

                                September 2012                          DRM(7)

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