Comment # 77 on bug 102646 from Garrett

small change to a comment above:

sudo -i
echo "manual" > /sys/class/drm/card0/device/power_dpm_force_performance_level 
echo "2" > /sys/class/drm/card0/device/pp_dpm_sclk (notice NOT pp_dpm_mclk)

allows my 75hz display to work without flicker at 75hz with RX580. it was
driving me INSANE that i couldnt use my monitors native refresh. have to do
this every reboot, which is annoying, but it works.

Note: using Solus Budgie with kernel 5.0.5-113...ymmv