FreeBSD kernel DRM device code
FreeBSD kernel DRM device code Documentation

The Direct Rendering Manager (DRM) is a device-independent kernel-level device driver that provides support for the XFree86 Direct Rendering Infrastructure (DRI).

The DRM supports the Direct Rendering Infrastructure (DRI) in four major ways:

  1. The DRM provides synchronized access to the graphics hardware via the use of an optimized two-tiered lock.
  2. The DRM enforces the DRI security policy for access to the graphics hardware by only allowing authenticated X11 clients access to restricted regions of memory.
  3. The DRM provides a generic DMA engine, complete with multiple queues and the ability to detect the need for an OpenGL context switch.
  4. The DRM is extensible via the use of small device-specific modules that rely extensively on the API exported by the DRM module.