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Secondary monitor does not come up with 6.10 (bisected to 8b2cb32cf0c)

Brief summary of the problem:

The monitor simply does not come up in wayland-plasma6 (it does in console). It appears as if it was there (windows open there and mouse cursor can go there), but the monitor is DPMS off.

There is no difference in dmesg regarding [drm].

I bisected the issue to:

commit 8b2cb32cf0c613fd937ebb49a331798985f50826
Author: Hersen Wu <hersenxs.wu@amd.com>
Date:   Mon Mar 11 18:18:34 2024 -0400

    drm/amd/display: FEC overhead should be checked once for mst slot nums

Reverting the above commit on the top of 6.10 makes it work again.

Hardware description:

  • CPU: AMD Ryzen 7 PRO 7840U w/ Radeon 780M Graphics
  • GPU: 64:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Phoenix1 [1002:15bf] (rev dd)
  • System Memory: last_pfn = 0x105e300
  • Display(s): internal + external
  • Type of Display Connection: eDP + HDMI

System information:

  • Distro name and Version: openSUSE Tumbleweed
  • Kernel version: 6.10
  • Custom kernel: N/A
  • AMD official driver version: N/A

How to reproduce the issue:

Boot 6.10 with the monitor attached.

Attached files:

Log files (for system lockups / game freezes / crashes)

Downstream bug

https://bugzilla.suse.com/show_bug.cgi?id=1228093

Edited by Jiri Slaby