https://bugs.freedesktop.org/show_bug.cgi?id=102646
--- Comment #31 from Timothy Pearson tpearson@raptorengineering.com --- (In reply to L.Y. Sim from comment #30)
I have this issue on a 3840x1600 Acer XR382CQK with an RX560 with Kernel 4.18.5-1 on Manjaro.
When I set the refresh rate to 75Hz, severe artifacts and flickering appear.
Both
echo high > /sys/class/drm/card0/device/power_dpm_force_performance_leveland
echo low > /sys/class/drm/card0/device/power_dpm_force_performance_levelstop the flickering and artifacting, and I can see via
cat /sys/class/drm/card0/device/pp_dpm_mclkthat the memory clocks are set to 1750Mhz and 300Mhz respectively.
However, if /sys/class/drm/card0/device/power_dpm_force_performance_level is set to auto, I can see (via watching /sys/class/drm/card0/device/pp_dpm_mclk with time intervals around 0.1s), that the memory clock oscillates rapidly between 300Mhz, 625Mhz and 1750Mhz.
So it seems to me that the rapid change in memory frequency is what's causing the flickering.
Confirmed here on a Polaris 10 GPU (WX7100) on DisplayPort with the latest kernel master from GIT (4.19+). The workaround sequence above stops the irritating flickering. dc=0 alone does /not/ stop the flickering, and dc=1 yields no displays detected due to some other bug.