Slow framerate regression on monitor connected through USB dock (bisected to fa57924c76d9)

Brief summary of the problem:

The general symptom is slow framerate or choppy/laggy performance on monitors connected through a USB dock.

I bisected the issue on the stable tree.

To reproduce the issue, run mangohud eglgears_wayland in Sway 1.10.

• On fcf6a49d7992, I see approx. 60fps (matching the refresh rate of the monitor).
• On the next commit, fa57924c76d9, (and all subsequent commits tested) I see approx. 30fps.

This performance issue persists for all subsequent kernel versions I've tested, up to 6.11.4.

Hardware description:

• CPU: AMD Ryzen 7 PRO 6850U with Radeon Graphics (family: 0x19, model: 0x44, stepping: 0x1)
• GPU: 04:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Rembrandt [Radeon 680M] [1002:1681] (rev d1)
• System Memory: 32G
• Display(s): Samsung LU28R55
• Type of Display Connection: HDMI, through USB-C dock.
• Laptop: ThinkPad P16s Gen 1

System information:

• Distro name and Version: Debian Testing
• Kernel version: Linux thinky1 6.11.4-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.11.4-1 (2024-10-20) x86_64 GNU/Linux
• Custom kernel: n/a
• AMD official driver version: n/a (amdgpu)

How to reproduce the issue:

1. Connect the monitor through the dock.
2. Start sway.
3. Open a terminal.
4. Run mangohud eglgears_wayland.
5. See low framerate displayed by mangohud.

Note that there is no such issue on the laptop's built-in monitor. There I get 60fps.

Attached files:

Screenshots/video files

Last good commit (6.9.0-rc5-01612-gfcf6a49d7992)

First bad commit (6.9.0-rc5-01613-gfa57924c76d9)

Still broken with most recent stable kernel in Debian testing (6.11.4)

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

n/a