(In reply to Christian König from comment #3)
> That could just be a symptom of a hardware hang which isn't detected for
> some reason.

There's this - drm/amdgpu: disable GPU reset by default

http://cgit.freedesktop.org/~agd5f/linux/commit/?h=drm-next-4.3&id=a895c222e7ab5f50ec10e209cd4548ecd5dd9443