https://bugs.freedesktop.org/show_bug.cgi?id=100058
--- Comment #3 from Michel Dänzer michel@daenzer.net --- (In reply to Adam Wolk from comment #0)
I noticed my external display constantly turning on and off unless a DRI app is active (ie. running DRI_PRIME=1 glxgears).
Which GPU is the external display connected to? If you're not sure, attach the output of xrandr.