Overdrive doesn't work either with current stable kernel (4.16.6). Clock
remains stable (as seen in amdgpu_pm_info) and reading the value gives 0:

> echo 5 | sudo tee /sys/class/drm/card0/device/pp_sclk_od
5
> cat /sys/class/drm/card0/device/pp_sclk_od
0

I can't currently tell when this issue appeared or if the feature even ever
worked with this hardware, as I've never been using it.