comment #32 is really all you need right now. I tried it in Arch Linux and it
also works like a charm. Just follow instructions on comment #77 for the "k"
firmware and you're good to go. You shouldn't need to change anything in
"/sys/class/drm/card0/device/power_dpm_force_performance_level", since this was
to avoid the problem. Now the default behaviour (the automated dpm one) works
with latest firmware.

I hope you can get it to work too :).