https://bugs.freedesktop.org/show_bug.cgi?id=66963
--- Comment #143 from Alex Deucher agd5f@yahoo.com --- (In reply to comment #142)
r600_enable_sclk_control(rdev, true);
r600_enable_sclk_control(rdev, false);
Does indeed fix it.
Unfortunately, that disables dynamic engine scaling which on your particular board pretty much disables dpm since the voltage and mclk are static :(