Alex I use something like that:
watch -n 1 -c "cat /sys/kernel/debug/dri/0/amdgpu_pm_info"
combined with 
vblank_mode=0 glxgears
it should set mclk on fire IIRC, but it was still 300MHz, bisecting gives me:
https://cgit.freedesktop.org/~agd5f/linux/commit/?h=drm-next-4.10-wip&id=ddfe1db18752b08d88d81cb7b661e1f982fc5d04

but when I've tested (in the bisecting proces) commit [1] I saw that mclk i set
always on 2000MHz... and this is first commit (I checked +/- 1) when is set on
HIGH no matter what.

So yes, this are two issues in one I believe because revert
1b7eab1f8346ab3b8e4fc54882306340a84497a8 fixes them all.