====== Ubuntu - GPU - DRM and DRI ======

**DRM** (Direct Rendering Manager) is a subsystem of the Linux kernel responsible for interfacing with GPUs of modern video cards.

  * DRM exposes an API (libdrm) that user-space programs can use to send commands and data to the GPU and perform operations such as configuring the mode setting of the display. 
  * **libdrm** makes it easy to access the DRM (Direct Rendering Manager) on the operating system.

DRM uses a set of generic system ioctls to allocate memory for the graphical objects and stuffs the commands and texture it needs.

  * The [[https://man7.org/linux/man-pages/man2/ioctl.2.html|ioctl]] system is a special type of system call that deals with device-specific input and output operations.
  * In this case, it deals with the input and output operations of a video card.

So, when we a graphical application is run, it loads the OpenGL driver, such as Mesa; which in turn, loads libdrm, which enables talking directly to the kernel through ioctl.

The window system, such as X Server or Wayland, needs to know what is happening, so it can synchronize and update itself.

  * This synchronization process is known as **DRI** (Direct Rendering Infrastructure).

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{{:ubuntu:gpu:gpu_-_drm_dri.png?400|}}

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[[Ubuntu:GPU:DRM:Get DRM Info|Get DRM Info]]