Just to add my 2c to this issue: if I set radeon.dpm=0 on the command line, the card defaults to the "profile" power method. If I try to: echo "high" > /sys/class/drm/card0/device/power_profile the screen goes black and I have to shut down using the power button (Ctrl+Alt+Del doesn't even work). This happens both while on the desktop or in another vt.