RX 570
1002:67df [AMD/ATI] Ellesmere [Radeon RX 470/480/570/570X/580/580X/590] (rev
ef)
Kernel: 4.19.2-300.fc29.x86_64
1920x1080     59.93*+

Lots of strange flickering and black lines with dc=1. Strange ghosting and
screen corruption with dc=0

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

Fixes the issue.

echo "2" >  /sys/class/drm/card0/device/pp_dpm_mclk
echo "0" >  /sys/class/drm/card0/device/pp_dpm_mclk
echo "2" >  /sys/class/drm/card0/device/pp_dpm_mclk

Produces screen corruption for half a second on each change. Across all 3
monitors.