As I tried to explain this a few times in the past to others and had trouble myself, when I started using Linux, I thought I take some time today and write down what parts comprise the Linux graphics stack and how they interact. I'll ignore some parts which aren't too interesting to an average user at the moment, to keep this post as consise as possible. Apart from that, I hope I'm able to put all the relevant data into one spot. Let us start our little journey in the kernel. There, in a directory named gpu you'll find the drm directory, which contains all DRM drivers. In this post, we'll focus on those. The drivers in that directory are the kernel side of the Direct Rendering Infrastructure (DRI) and are responsible for managing concurrent access to the graphics hardware. They also provide interfaces to pass commands and data to the GPU. The DRI wiki explains the three main purposes of the DRM modules. The DRM module is also the part that decides whether KMS or UMS is used. Other acronyms you might hear with regard to graphics acceleration on Linux and are referring to the Kernel part are: GEM: an Intel-developed memory management system for GPUs.
TTM: refers to the memory management system used by almost all non-Intel drivers (e.g. AMD's Radeon drivers). The TTM interface is "GEM-ified", meaning it offers the same API as GEM.Apart from that, every driver has its hardware-specific parts like utilizing power-saving functions of the respective GPUs, loading firmware, if required, etc. Now we move from Kernel space to user land. We'll ignore any non-X and non-Mesa parts (like acceleration for TTYs). That means, that our next GPU specific part is most likely the DDX. (Please note, that the classic DDX might be replaced by a Gallium3D state tracker, currently that would be the xorg state tracker, but xorg will be replaced by XA. This is only an option if the Gallium driver for your GPU supports one of those state trackers, see the Gallium status page for further details.) The DDX for your GPU offers plain (2D) X acceleration on your hardware. The respective DDX' are generally named xf86-video-[NAME], where [NAME] is replaced by e.g. ati or intel. The DDX decides which X acceleration paths are available. Acronyms you might hear, referring to the DDX part of the graphics stack, are: EXA: even though it looks like an acronym, the X.Org wiki Glossary defines it as: acceleration architecture with no well-defined acronym EXA superseded the older XAA and offers 2D acceleration, often in conjunction with XRender.
UXA: more or less EXA for Intel GPUs.
GLX: actually not a part of the DDX, but an extension for X. It provides a way to draw with OpenGL into an window managed by X.
XRandR: An extension for X which needs to be supported by the DDX to work. It offers a standardized way to set up (multiple) heads (e.g. resolution, position, rotation, etc.). Read more: Cùran's life
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TTM: refers to the memory management system used by almost all non-Intel drivers (e.g. AMD's Radeon drivers). The TTM interface is "GEM-ified", meaning it offers the same API as GEM.Apart from that, every driver has its hardware-specific parts like utilizing power-saving functions of the respective GPUs, loading firmware, if required, etc. Now we move from Kernel space to user land. We'll ignore any non-X and non-Mesa parts (like acceleration for TTYs). That means, that our next GPU specific part is most likely the DDX. (Please note, that the classic DDX might be replaced by a Gallium3D state tracker, currently that would be the xorg state tracker, but xorg will be replaced by XA. This is only an option if the Gallium driver for your GPU supports one of those state trackers, see the Gallium status page for further details.) The DDX for your GPU offers plain (2D) X acceleration on your hardware. The respective DDX' are generally named xf86-video-[NAME], where [NAME] is replaced by e.g. ati or intel. The DDX decides which X acceleration paths are available. Acronyms you might hear, referring to the DDX part of the graphics stack, are: EXA: even though it looks like an acronym, the X.Org wiki Glossary defines it as: acceleration architecture with no well-defined acronym EXA superseded the older XAA and offers 2D acceleration, often in conjunction with XRender.
UXA: more or less EXA for Intel GPUs.
GLX: actually not a part of the DDX, but an extension for X. It provides a way to draw with OpenGL into an window managed by X.
XRandR: An extension for X which needs to be supported by the DDX to work. It offers a standardized way to set up (multiple) heads (e.g. resolution, position, rotation, etc.). Read more: Cùran's life
QR:
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