Created attachment 81098 [details]
I'm running the latest git from Linus's tree with xf86-video-ati libdrm and mesa from git
The lockup seems to happen when video is playing. It's Xv rather than vdpau that seems to cause this
Created attachment 81099 [details]
Does setting the env var RADEON_VA=0 in your /etc/environment fix the issue? This looks like a mesa issue.
I've not had another lockup since doing this