Comment # 30 on bug 82201 from Alex Deucher

(In reply to comment #29)
> # echo "auto" >
> /sys/class/drm/card0/device/power_dpm_force_performance_level 
> bash: echo: write error: Invalid argument
> 
> Not sure, what valid options would be for me.

auto, high, and low are the valid options.  You are getting an error because
the hw rejected your request.