[Bug 107731] radeon (amdgpu) DisplayPort loss of max-resolution on DP monitor (after monitor power saving / idle)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107731

--- Comment #1 from L.S.S. <ragnaros39216 at yandex.com> ---
Having similar issues with Manjaro Linux (4.20 Kernel) and AMD video cards.

I've a 4K at 60Hz capable monitor (Lenovo ThinkVision P27) and an ATEN CS1924 KVM
behind it (as I need to use this monitor for 4 different PCs). I've two PCs
with Manjaro Linux and AMD GPU, and I can 100% reproduce the issue on both of
them.

This happens whenever I power off the monitor (or when it went idle). After
powering the monitor back on, it reverts to a lower resolution (During most
cases, xrandr reported max 2048x1536 but it actually picked 1792x1344. Recently
I also noticed sometimes xrandr would report only 800x600).

It can be fixed by switching the input channel back and forth on the KVM (which
I think is equivalent to unplugging and replugging the DP port).

On one of the PCs, it used to have an nVidia video card before replacing it
with Radeon VII. With an nVidia video card, this issue did not occur (using
same configuration).

When this happens, I can find this red line in dmesg. Other log entries are
mostly about on-monitor USB hubs and such, and they're irrelevent to the issue
from the look of it.

[drm:dm_restore_drm_connector_state [amdgpu]] *ERROR* Restoring old state
failed with -22

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