https://bugzilla.kernel.org/show_bug.cgi?id=207383
--- Comment #5 from Duncan (1i5t5.duncan@cox.net) --- Well, that didn't take long. Four konsole terminals open to do (various aspects of) a system update. Just a few seconds after I entered the (git-based) sync command, display-FREEZE!
Back on 5.6.0 now. I'll probably test again with rc4, perhaps earlier if I see a set of drm/amdgpu updates in mainline git.