[PATCH xserver] present: Only requeue for next MSC after flip failure

[Adam Jackson]

On Thu, 2016-03-24 at 07:22 -0600, Keith Packard wrote:
> Michel Dänzer <michel at daenzer.net> writes:
> 
> > 
> > From: Michel Dänzer <michel.daenzer at amd.com>
> > 
> > This code was added to deal with the driver present hook failing, in
> > which case we need to wait for the next MSC before executing the
> > presentation.
> > 
> > However, it could also take effect in cases where the driver incorrectly
> > thinks the current MSC matches the target one (e.g. due to the kernel
> > interface only supporting 32-bit MSC values), in which case it could
> > result in the presentation getting requeued over and over.
> > 
> > To prevent such issues, check specifically for the target MSC
> > immediately following the current MSC.
> Yeah, I think this is reasonable. I wondered if we should use a broader
> range than == 1, but really that's the only case that's interesting;
> either the flip vblank is getting executed in the MSC it was supposed
> to, in which case vblank->target_msc will be exactly crtc_msc+1, or it's
> being done late, in which case that will have passed and we'll copy it
> immediately.

Huh.  That actually means we're pretty close to supporting
GLX_EXT_swap_control_tear properly.  Nice.

remote: I: patch #78156 updated using rev 3b385105b2d19a1c55e9779ae88d775185eea231.
remote: I: 1 patch(es) updated to state Accepted.
To ssh://git.freedesktop.org/git/xorg/xserver
   8ac0e05..3b38510  master -> master

- ajax