Will test patch sometime later, as it happens I built latest 4.6-wip last night
and managed to see memclk stuck without (knowingly) touching UVD.

I was running with auto and it's quite possible that leaving alone and running
another high usage gl app would have worked, but to test I tried forcing and
got -

Feb  5 00:38:44 ph4 kernel: Failed to send Message.
Feb  5 00:38:44 ph4 kernel: [ powerplay ] Target_and_current_Profile_Index.
^I^I^I^I^I^ICurr_Mclk_Index does not match the level 
Feb  5 00:38:47 ph4 kernel: Failed to send Previous Message.

In addition after that I rebuilt latest llvm/mesa which has resulted in dmesg
full of vmfaults, so I now need to sort that first.