backend-drm: dont emit sesion signal if already at same state

Graphics / Wayland / Weston - Robert Beckett [] - 18 July 2019 06:35 EDT

logind will send a device changed at start of day, prompting a session active change, but the session will already be active from compositor creation.

Avoid unnecessary signal emition and drm state invalidation.

The logind launcher sets the session active when the graphics device is assigned to weston from systemd. Unfortunately 8d23ab78 didnt check whether the session was already active before setting it active and emitting the session active signal. The handler for that signal then proceeds to invalidate the entire graphics state, causing the next redraw to reconfigure all outputs (to the same routing as they were already). This then massively increases the likelihood of trying to configure a crtc that has a commit already in flight.

Add the old behaviour of only emitting a signal on a changed state. This avoids the issue for now by reducing the chances of a clash. Future work will need to fix the issue properly (better handling of state_invalid e.g. wait for quiescence, better monitoring for crtc usage clashes etc).

49dc3201 backend-drm: dont emit sesion signal if already at same state
libweston/backend-drm/drm.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)


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