Xorg driver explanation on Linux?

[Bridgman, John]

))It looks like Xorg drivers on Linux platform are NOT kernel modules. Could someone explain, or better point some brief document - what these Xorg drivers are and how they are implemented ?

Sorry about the top-posting, let's try that again :)

The xorg drivers run in userspace, called by the X server. Where things get confusing is that they can be written to operate in at least different ways.

Basic 2d-only drivers can directly access the hardware from userspace for both modesetting and acceleration,  and can run without a kernel driver. This was the norm 10-15 years ago and many drivers can still fall back to this mode.

Drivers from a few years ago tend to access modesetting hardware from userspace but go through a kernel driver for acceleration, allowing the acceleration hardware to be shared with a separate 3d driver. Using the kernel driver to coordinate access to acceleration hardware is part of the Direct Rendering Infrastructure (DRI).

The most recent xorg drivers use the kernel driver for essentially all hardware accesses, including modesetting. Moving modesetting into the kernel driver was an initiative called (predictably) Kernel ModeSetting or KMS.