https://bugs.freedesktop.org/show_bug.cgi?id=105308
--- Comment #4 from Michel Dänzer michel@daenzer.net --- While the problem is occurring, and the screen contents are being updated at least once per second, please run the following as root:
echo 255 >/sys/module/drm/parameters/debug"; sleep 1; echo 0
/sys/module/drm/parameters/debug
and attach the resulting dmesg output.