[Intel-gfx] [PATCH 1/2] drm/framebuffer: Format modifier for Intel Gen 12 render compression with Clear Color

[Imre Deak]

On Fri, Dec 11, 2020 at 09:04:02AM +0200, Chery, Nanley G wrote:
> [...]
> > > We probably don't have to update the header, but we noticed in our
> > > testing that the clear color prefers an alignment greater than 64B.
> > > Unfortunately, I can't find any bspec note about this. As long as the
> > > buffer creators are aware though, I think we should be fine. I don't
> > > know if this is the best forum to bring it up, but I thought I'd
> > > share.
> > 
> > Yes, would be good to clarify this and get it also to the spec. Then the
> > driver should also check the alignment of the 3rd FB plane.
> 
> I plan to run some more tests and file a bug in the spec.

Ok, thanks. Note that this patch has a problem with synchornization and
based on Chris' response I'm planning to update it once I figured out
the proper way to map the CC plane. Until that you could still use it on
TGL if you wait for the RT result explicitly after the fast clear and
before flipping to it (that's what the IGT test does atm).

> I see that the IGT test only clears the fb once. Just to confirm, is the 
> clear color offset read from on every frame? Userspace would like to be 
> able to pass different clear colors for an fb.

Yes, every time you do a flip the kernel will re-read the CC value and
program it to the display.

--Imre