[PATCH 2/4] drm/radeon: Allow vblank_disable_immediate.

[Michel Dänzer]

On 21/06/17 10:44 AM, Mario Kleiner wrote:
> With instantaneous high precision vblank timestamping
> that updates at leading edge of vblank, a cooked hw
> vblank counter which increments at leading edge of
> vblank, and reliable page flip execution and completion
> at leading edge of vblank, we should meet the requirements
> for fast/immediate vblank irq disable/enable.
> 
> Testing on Linux-4.12-rc5 + drm-next on a Radeon HD 5770
> (DCE 4) with timing measurement equipment indicates this
> works fine, so allow immediate vblank disable for power
> saving.
> 
> For debugging in case of unexpected trouble, booting
> with kernel cmdline option drm.vblankoffdelay=0
> (or echo 0 > /sys/module/drm/parameters/vblankoffdelay)
> would keep vblank irqs permanently on to approximate old
> behavior.
> 
> Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
> Cc: Alex Deucher <alexander.deucher at amd.com>
> Cc: Michel Dänzer <michel.daenzer at amd.com>

My only doubt is whether this is also reliable on older (e.g. pre-R600)
GPUs. For newer GPUs (tested on Kaveri):

Reviewed-and-Tested-by: Michel Dänzer <michel.daenzer at amd.com>


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer