[Bug 110199] [amdgpu] Screen flickering when using a 75Hz monitor paired with an RX 480 GPU

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110199

            Bug ID: 110199
           Summary: [amdgpu] Screen flickering when using a 75Hz monitor
                    paired with an RX 480 GPU
           Product: DRI
           Version: XOrg git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: critical
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: m.ivanov2k at gmail.com

My monitor is LG 24MP59G-P (75Hz, FreeSync) and my GPU is Sapphire Nitro+ RX
480 8GB.

Basically, whenever there is movement on my screen (oddly though, cursor
movement doesn't cause it), it would flicker very badly. 

Here is a video of what I am talking about: https://streamable.com/5eu7p

Apart from trying different refresh rates, as seen in the video, I have also
tried switching kernel versions, switching from DisplayPort to HDMI, changing
compositor settings and turning off FreeSync from the monitor OSD, but nothing
seems to resolve the bug.

What works for me as a workaround is changing
/sys/class/drm/card0/device/power_dpm_force_performance_level from auto to
either low or high. When I do watch -n 1
"/sys/class/drm/card0/device/pp_dpm_mclk" with the performance level on auto,
it normally stays on the lowest (300MHz) and when I move a window around, it
constantly switches from 300MHz to 2000MHz (the max on my GPU). Apparently,
that's what's causing it to behave this way.

I should emphasize, that I observed the bug in Antergos, Debian 9 Buster
(Stretch is good), Manjaro XFCE, Manjaro KDE, Ubuntu 18.10, KUbuntu 18.04 and
KUbuntu 18.10. At first I thought it was only related to Arch Linux
derivatives, since they all use bleeding-edge packages, but then I noticed,
that after switching Debian 9 Stretch's (stable) sources to Buster (testing)
and after updating KUbuntu 18.10, the bug appeared in both distros as well.

Here is a link to a thread I created in the Manjaro forums, where I asked for
help:
https://forum.manjaro.org/t/manjaro-kde-screen-flickering-cant-seem-to-find-a-solution/78349
- You can find all kinds of different things I tried there, as well as more
in-depth system information.

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