Bug#523972: xserver-xorg-video-radeon:

[John Lewis]

Package: xserver-xorg-video-radeon
Version: 1:7.5.0-1
Followup-For: Bug #523972

I had similar issues with an R7 360. I have more information on this
thread. https://lists.x.org/archives/xorg/2016-September/058291.html