Comment # 7 on bug 89196 from Alex Deucher

(In reply to Maciej Gluszek from comment #6)
> UPDATE:
> 
> I removed all additional tested kernel command lines that apply to Radeon
> besides radeon.dpm=1 for power management.

> Lockups are still happening. I cannot specify which application is causing
> this. Lockups happen completly at random times.

dpm is disabled by default on rv6xx due to stability issues.  It's likely that
may be the problem you are seeing.  In that case, this bug is a duplicate of
bug 66963.