[Bug 94903] Tahiti and Hawaii (without amdgpu support) skips vblanks on wayland (weston and others) on some displays.

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94903

            Bug ID: 94903
           Summary: Tahiti and Hawaii (without amdgpu support) skips
                    vblanks on wayland (weston and others) on some
                    displays.
           Product: Mesa
           Version: git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: major
          Priority: medium
         Component: Drivers/Gallium/radeonsi
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: johngaltfirstrun at gmail.com
        QA Contact: dri-devel at lists.freedesktop.org

When running weston on this hardware with Shimian QHD270 displays, vblanks are
skipped resulting in stuttering video playback on any framerate other than
60fps (with multiple players and vo including opengl and wayland (shm)).
System:
Mesa: git
linux: 4.4, 4.5, 4.6 from a drm-next-wip branch
wayland: git
weston: git

A few notes:
 - This doesn't occur when using amdgpu (for instance building with hawaii
amdgpu support.
 - This bug goes back as far as a year, and another user verified they had this
issue on a radeonsi card with a specific monitor.
 - When utilizing amdgpu, the EDID is correctly read from these monitors.
Without, the EDID read fails. I've written the EDID to a file in /lib/firmware/
and successfully loaded with no change however.
 - Outside of video playback, there are no vblank skips. It was explained that
each application affects the entire compositor.
 - No change on video size. The issue is apparent (with no discernible change)
on non-60fps 360p youtube videos on up to high bitrate x265 4K tv shows.
 - By increasing repaint-window, I'm able to get consistent playback and no
vblank skips. However I do run into other issues with it, showing it's clearly
not a real solution for wayland support on radeon.
 - During video playback, weston-presentation-shm shows the missing vblanks
just as a timeline does (so including weston-presentation-shm log for
readability instead).

weston-presentation-shm log with video playback at beginning:
https://bpaste.net/show/f8c9b910ddc1. When vblanks are no longer skipped, the
video playback has stopped.

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