drivers/gpu/drm/radeon/Kconfig

config DRM_RADEON_KMS
	bool "Enable modesetting on radeon by default - NEW DRIVER"
	depends on DRM_RADEON
	select BACKLIGHT_CLASS_DEVICE
	help
	  Choose this option if you want kernel modesetting enabled by default.

	  This is a completely new driver. It's only part of the existing drm
	  for compatibility reasons. It requires an entirely different graphics
	  stack above it and works very differently from the old drm stack.
	  i.e. don't enable this unless you know what you are doing it may
	  cause issues or bugs compared to the previous userspace driver stack.

	  When kernel modesetting is enabled the IOCTL of radeon/drm
	  driver are considered as invalid and an error message is printed
	  in the log and they return failure.

	  KMS enabled userspace will use new API to talk with the radeon/drm
	  driver. The new API provide functions to create/destroy/share/mmap
	  buffer object which are then managed by the kernel memory manager
	  (here TTM). In order to submit command to the GPU the userspace
	  provide a buffer holding the command stream, along this buffer
	  userspace have to provide a list of buffer object used by the
	  command stream. The kernel radeon driver will then place buffer
	  in GPU accessible memory and will update command stream to reflect
	  the position of the different buffers.

	  The kernel will also perform security check on command stream
	  provided by the user, we want to catch and forbid any illegal use
	  of the GPU such as DMA into random system memory or into memory
	  not owned by the process supplying the command stream.