Comment # 9 on bug 96964 from Timothy Pearson

A bit more information:
 * Disabling DPM does not fix the problem (dpm=0 on module load)
 * Using hard reset instead of soft reset just makes a complete mess / host
hang
 * It looks like only the CP block needs to be reset (GPU softreset: 0x00000008
corresponds to RADEON_RESET_CP).
 * After reset DPM is broken, but DPM also breaks after unloading / reloading
the radeon module so this may be a red herring.