[Wayland-bugs] [Bug 83884] New: Recover from missing DRM completion events

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=83884

          Priority: medium
            Bug ID: 83884
          Assignee: wayland-bugs at lists.freedesktop.org
           Summary: Recover from missing DRM completion events
          Severity: enhancement
    Classification: Unclassified
                OS: Linux (All)
          Reporter: ppaalanen at gmail.com
          Hardware: All
            Status: NEW
           Version: unspecified
         Component: weston
           Product: Wayland

Add a watchdog to the DRM backend that will recover Weston, if the DRM page
flip events stop coming.

Weston relies on those events, and will normally not repaint until the previous
update has been acked. However, on buggy DRM drivers, and now that we are
getting closer to the universal planes and atomic mode setting and page
flipping framework, it is quite likely that some drivers are sometimes buggy.
Recovering from buggy drivers while still clearly signalling the failure should
help developers in testing their drivers.

How to recover?
Some options:
- gracefully quit Weston with an error
- fall back to immediate, timer throttled display updates (drmModeSetCrtc /
drmModePageFlip without events) and hope it works

Need to take care to not cause the watchdog to trigger during e.g. VT-switched
away, or during high load.

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