https://bugs.freedesktop.org/show_bug.cgi?id=88364
--- Comment #3 from Michel Dänzer michel@daenzer.net --- (In reply to Liss from comment #2)
If I restart notebook and try to run something again I'll get black window (Xorg will continue to work)
Note that DRI_PRIME currently requires a compositing manager for the contents to be visible.
and next dmesg log:
Looks like the normal messages from powering up and initializing the Radeon GPU.