Is the bug related to
https://cgit.freedesktop.org/xorg/xserver/commit/?id=21eda7464d0e13ac6558edaf6531c3d3251e05df
A possible patch would then be:
diff --git a/hw/dmx/dmxsync.c b/hw/dmx/dmxsync.c
index 1bc2423..b55c9dd 100644
--- a/hw/dmx/dmxsync.c
+++ b/hw/dmx/dmxsync.c
@@ -182,7 +182,7 @@ dmxSync(DMXScreenInfo * dmxScreen, Bool now)
/* Do sync or set time for later */
if (now || !dmxScreen) {
- if (!TimerForce(dmxSyncTimer))
+ if (dmxSyncTimer == NULL || !TimerForce(dmxSyncTimer))
dmxSyncCallback(NULL, 0, NULL);
/* At this point, dmxSyncPending == 0 because
* dmxSyncCallback must have been called. */
--
Eric
