Adding this check was prompted by
https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/609
There is no reason to allow frame times jump backwards, and apparently
we already have code that makes that assumption.
DRM KMS uses CLOCK_MONOTONIC as the vblank and page flip timestamps,
which by definition cannot go backwards. Other backends call
weston_compositor_set_presentation_clock_software().
Frame times are also reported directly to Wayland clients via
presentation-time extension, and clients too will not expect that the
timestamp could go backwards.
So make sure time can never go backwards.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Pekka Paalanen
98b4e20a68