[Wayland-bugs] [Bug 79502] Weston needs to detect when DRM pageflip timestamps are not supported

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=79502

Frederic Plourde <frederic.plourde at collabora.co.uk> changed:

           What    |Removed                     |Added
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             Status|NEW                         |ASSIGNED

--- Comment #2 from Frederic Plourde <frederic.plourde at collabora.co.uk> ---
This patch :
http://cgit.freedesktop.org/~fredinfinite23/weston/commit/?h=bad_timestamp_abort&id=507cfb65fba6ed2f4e0b3973f6335ba98aa97894
is a fix for this,

but I'd like to discuss it some more, because I feel there is something
missing:

1) False-positive detection:
   What if DRM driver 'sanely' returns a timestamp = 0 either by (mis)chance or
because of some weird DRM initial condition/behavior (first frame ?). We should
be given another chance to repaint.

2) Integer overflows:
   What if we arrived at frame_time's max_range ? Next timestamp would then
break the 'cur > prev' rule and we would wrongly abort Weston.

I think those two considerations above call for some 'counter' on the
detection. Chances that we 'sanely' hit (stamp==0 || cur < prev) are really
low, but chances that we hit that twice in a row are practically 0. I don't see
any need for a customizable counter; I would set it to 1 by default and exit
Weston when it's 0.

opinions on that please :)

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