https://bugs.freedesktop.org/show_bug.cgi?id=66963
--- Comment #241 from Alex Deucher agd5f@yahoo.com --- (In reply to comment #239)
echo high > /sys/class/drm/card0/device/power_dpm_force_performance_level
echo performance > /sys/class/drm/card0/device/power_dpm_state
This is effectively the same as disabling dpm.