[RFC] drm/atomic: Abuse legacy cursor update flag for legacy gamma update too

[Ville Syrjälä]

On Tue, Feb 13, 2018 at 10:33:28AM +0100, Maarten Lankhorst wrote:
> Hey,
> 
> Op 13-02-18 om 10:16 schreef Chris Wilson:
> > Quoting Maarten Lankhorst (2018-02-13 09:12:01)
> >> Programs like redshift set the legacy gamma for X.org every 5 seconds.
> >> Because atomic commits wait for vblank completion, we get a frame drop
> >> every 5 seconds because of the legacy gamma update.
> >>
> >> Work around this by setting the legacy_cursor_update flag, to force
> >> legacy gamma updates not to be synced against vblank.
> >>
> >> Reported-by: Tholin #intel-gfx
> >> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> > Reminiscing: Remember the time we had all those vblank workers patches,
> > one of which was to do async gamma updates (apply the last one on the
> > vblank). Motivated by gnome-shell and the ilk doing a gamma animation
> > for fade-out on logout (which I guess they gave up on since it happened
> > to be so slow as to extend logout ;).
> 
> That special case could be handled by userspace with atomic commits, I don't
> think it's worth optimizing it further..

We need to eventually move the gamma updates (and other single buffered
registers) to a vblank worker or something similar. Otherwise they will
tear.

-- 
Ville Syrjälä
Intel OTC