Comment # 10 on bug 109239 from Samuel Pitoiset

I don't think it's a cable issue because it works fine with NVIDIA.

echo manual > /sys/class/drm/card0/device/power_dpm_force_performance_level
echo "0" >  /sys/class/drm/card0/device/pp_dpm_mclk

Doing this doesn't fix the problem.

Anything else?