[Bug 109359] Flickering and artifacts on dual 4K displays from RX 570

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109359

            Bug ID: 109359
           Summary: Flickering and artifacts on dual 4K displays from RX
                    570
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: venemo at msn.com

There are two Dell U2718Q 4K monitors connected to a Sapphire Pulse RX 570 ITX
card, one using the DisplayPort output and the other using the HDMI output.

There is a visible flickering artifact on both displays. There is no problem
when only a single display is connected.

Searching online yields a couple of results that suggest a workaround: manually
increasing the shader and/or memory clock of the GPU. On the RX 570 the
following commands can get rid of the problem:

echo "manual" > /sys/class/drm/card0/device/power_dpm_force_performance_level
echo "2" > /sys/class/drm/card0/device/pp_dpm_mclk
echo "5 6 7" > /sys/class/drm/card0/device/pp_dpm_sclk

However, I believe the amdgpu driver should be able to figure out the correct
necessary clock settings on its own. The problem exists in Linux 4.19 and
5.0-rc1 as well.

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