Comment # 20 on bug 71448 from Alex Deucher

(In reply to comment #19)
> 
> What do you mean by "plain video playback"? If you mean without using vdpau
> it works flawlessly.

Just play a video with vdpau using mplayer or some other app that supports
vdpau.  I'm wondering if perhaps the way qvdpautest works causes the driver to
switch between power states too often so the clocks never get a chance to
stablize.