[Bug 78713] New: Vertical sync (vsync) broken on Radeon Zaphod mode

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=78713

          Priority: medium
            Bug ID: 78713
          Assignee: xorg-driver-ati at lists.x.org
           Summary: Vertical sync (vsync) broken on Radeon Zaphod mode
        QA Contact: xorg-team at lists.x.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: chewi at aura-online.co.uk
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: git
         Component: Driver/Radeon
           Product: xorg

I know that vsync worked on Radeon Zaphod mode when bug #29726 was fixed but it
has broken at some point since. I am now observing tearing in glxgears even
when it reports that vsync is enabled. Unfortunately I have no idea exactly
when it broke. The good news is I have a very strong clue as to what the
problem is. If you remove this line...

http://cgit.freedesktop.org/xorg/driver/xf86-video-ati/tree/src/radeon_dri2.c?id=be1469cc23aba46daf3293b3d09c5f2e792e7f42#n480

...then it works. Why? I wish I knew. It was just a very lucky stab in the
dark. This line was around a good deal before bug #29726 was fixed so
presumably its interaction with something else must have changed in the
meantime. SwapbuffersWait is definitely enabled.

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