https://bugs.freedesktop.org/show_bug.cgi?id=66963
--- Comment #259 from Maciej Gluszek info@maciejgluszek.com --- Sorry, I was wrong after all. After 2 days i got a lockup again and went back to the old method.
When i don't set DPM at boot GPU is overheating and the fan goes crazy. When setting performance to something other than "high" - lockups happen.
I'm on Ubuntu 14.04 and using kernels from http://kernel.ubuntu.com/~kernel-ppa/mainline/