(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_level
> and
> 
>     echo low > /sys/class/drm/card0/device/power_dpm_force_performance_level
> 
> stop the flickering and artifacting, and I can see via 
> 
>     cat /sys/class/drm/card0/device/pp_dpm_mclk 
> 
> that 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.