[Bug 220906] New: Regression: 4K display output fails on ThinkPad Thunderbolt 4 Dock with AMD GPU (Worked in 6.17.1, broken in 6.17.11)

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=220906

            Bug ID: 220906
           Summary: Regression: 4K display output fails on ThinkPad
                    Thunderbolt 4 Dock with AMD GPU (Worked in 6.17.1,
                    broken in 6.17.11)
           Product: Drivers
           Version: 2.5
          Hardware: AMD
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: Video(DRI - non Intel)
          Assignee: drivers_video-dri@kernel-bugs.osdl.org
          Reporter: danandrei@gmail.com
        Regression: No

Created attachment 309076
  --> https://bugzilla.kernel.org/attachment.cgi?id=309076&action=edit
dmesg boot output for 6.17.1 & 6.17.12

A regression in recent kernels prevents 4K output over a ThinkPad Thunderbolt 4
Dock when using amdgpu.

After upgrading to kernel 6.17.11‑300.fc43.x86_64 on a Lenovo T14s Gen 6 (AMD),
my 4K external monitor connected through a ThinkPad Thunderbolt 4 Dock no
longer works at 4K resolution. The display only shows output at lower
resolutions, and even those modes are effectively unusable.

This is a regression: the same hardware setup works correctly on kernel
6.17.1‑300.fc43.x86_64, including the version shipped with
Fedora‑KDE‑Desktop‑Live‑43‑1.6.x86_64.iso. Booting back into 6.17.1 restores
full 4K functionality.

The issue is fully reproducible by using the affected kernel versions with this
hardware combination. No out‑of‑tree modules are installed; this is a fresh
Fedora installation.

I also tested the latest Rawhide kernel (6.18 branch), and the problem persists
there as well.

When attempting to switch the display to 4K, the kernel logs repeatedly show
the following amdgpu messages:

```
journalctl -f | grep -i 'amdgpu'

Dec 14 22:37:37 GOTO kernel: amdgpu 0000:c3:00.0: amdgpu: [drm] DMUB HPD RX IRQ
callback: link_index=5
Dec 14 22:37:37 GOTO kernel: amdgpu 0000:c3:00.0: amdgpu: [drm] DMUB HPD RX IRQ
callback: link_index=5
Dec 14 22:37:37 GOTO kernel: amdgpu 0000:c3:00.0: amdgpu: [drm] DMUB HPD RX IRQ
callback: link_index=5
Dec 14 22:37:37 GOTO kernel: amdgpu 0000:c3:00.0: amdgpu: [drm] DMUB HPD RX IRQ
callback: link_index=5
Dec 14 22:37:37 GOTO kernel: amdgpu 0000:c3:00.0: amdgpu: [drm] DMUB HPD RX IRQ
callback: link_index=5
Dec 14 22:37:37 GOTO kernel: amdgpu 0000:c3:00.0: amdgpu: [drm] DMUB HPD RX IRQ
callback: link_index=5
Dec 14 22:37:37 GOTO kernel: amdgpu 0000:c3:00.0: amdgpu: [drm] DMUB HPD RX IRQ
callback: link_index=5
Dec 14 22:37:37 GOTO kernel: amdgpu 0000:c3:00.0: amdgpu: [drm] DMUB HPD RX IRQ
callback: link_index=5
Dec 14 22:37:37 GOTO kernel: amdgpu 0000:c3:00.0: amdgpu: [drm] DMUB HPD RX IRQ
callback: link_index=5
Dec 14 22:37:37 GOTO kernel: amdgpu 0000:c3:00.0: amdgpu: [drm] DMUB HPD RX IRQ
callback: link_index=5
Dec 14 22:37:38 GOTO kernel: amdgpu 0000:c3:00.0: amdgpu: [drm] DMUB HPD RX IRQ
callback: link_index=5
Dec 14 22:37:53 GOTO kernel: amdgpu 0000:c3:00.0: amdgpu: [drm] DMUB HPD RX IRQ
callback: link_index=5
Dec 14 22:37:53 GOTO kernel: amdgpu 0000:c3:00.0: amdgpu: [drm] DMUB HPD RX IRQ
callback: link_index=5
```

I noticed that Bug 219748 (Pluggable UD‑4VPD dock resetting on AMD hardware)
shows the same repeated [drm] DMUB HPD RX IRQ callback messages. The hardware
is similar and also involves a USB‑C/Thunderbolt dock, so this may be related.

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