Antonio Borneo authored Jun 30, 2019 and Daniel Stone committed Jul 12, 2019

Depending on system loading, weston-launcher could drop the drm
master access before the compositor and all the clients receive
the notification. In this case, some commit could be sent to the
drm driver too late and get refused with error EACCES.
This error condition is not properly managed and causes weston to
hang.

Change the return type of start_repaint_loop() and repaint_flush()
from void to int, and return 0 on success or -1 if the repaint has
to be cancelled.
In the callers of start_repaint_loop() and repaint_flush() handle
the return value and cancel the repaint when needed.
In backend-drm detect the error EACCES and return -1.
Note: to keep the code cleaner, this change inverts the execution
order between weston_output_schedule_repaint_reset() and
repaint_cancel().

No need to wait for suspend or for any notification; in case the
weston reschedules a repaint, it will get EACCES again.
At resume, damage-all guarantees a complete repaint.

This fix is for atomic modeset only.
Legacy modeset suffers from similar problems, but it is not fixed
by this change. Since drm_pending_state_apply() never returns
error for legacy modeset, this change has no impact on legacy
modeset.

Signed-off-by: Antonio Borneo <antonio.borneo@st.com>
Fixes: https://gitlab.freedesktop.org/wayland/weston/issues/117