[Bug 220304] New: [amdgpu] DisplayPort resource allocation issue (one blank screen)

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=220304

            Bug ID: 220304
           Summary: [amdgpu] DisplayPort resource allocation issue (one
                    blank screen)
           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: jonas@sldr.se
        Regression: No

I have a Lenovo laptop with an AMD Ryzen 7 (7840HS) and its integrated GPU ATI
Phoenix1. The laptop is connected to a Thunderbolt 4 Dell dock (WD22TB4)
through which it is connected to two 4K screens via DisplayPort. OS is NixOS.

The problem: after updating NixOS, my kernel jumped from 6.6.something to
6.12.something-else. During boot, all screens light up and show the boot
process, but as soon as X starts one of the external screens go dark,
complaining of no signal. X, however, still thinks the screen is there, showing
it as connected and functional. Changing the screen modes around can let me
change which screen loses signal, and reducing the resolution on one of them
brings them both back on, but then no longer in 4K. Switching the system back
to the 6.6 kernel (but still in the latest NixOS version) "fixes" the issue,
and both 4K screen work again.

After some bisecting, I've narrowed down the window where this problem was
introduced to somewhere between 6.9.0 and 6.10-rc1. I also tested later kernels
(6.13 and 6.14) which all showed the same issue. Opening this report to have it
reported, while I continue bisecting and hopefully finding the rough-ish source
of the problem.

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