(In reply to comment #10)
> If you are using dpm, make sure your ddx has this patch:
> http://cgit.freedesktop.org/xorg/driver/xf86-video-ati/commit/
> ?id=c4ae0e2cbcc0e2ebf9f13ee92d59b5120254a1dc

I am using the latest ddx from git. Enabling or disabling dpm using the kernel
option radeon.dpm=1 or radeon.dpm=0 does not help. It seems like the more
redraws the GPU has to do, the worse things get. For example, sitting at the
desktop with nothing moving is fine. Opening chromium, many horizontal lines
matching the color of whatever is on the screen begin to flicker on and off.

Is it possible that color tiling is the culprit as described in
https://bugs.freedesktop.org/show_bug.cgi?id=42621

His symptoms sound identical (only happens on 1920x1080 resolution, smaller
resolutions work).