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-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).

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)