[Bug 207595] New: [amdgpu] Displayport MST not functional on AMD Stoney

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=207595

            Bug ID: 207595
           Summary: [amdgpu] Displayport MST not functional on AMD Stoney
           Product: Drivers
           Version: 2.5
    Kernel Version: 5.4.28, 5.4.36
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - non Intel)
          Assignee: drivers_video-dri at kernel-bugs.osdl.org
          Reporter: jjo.braun at gmail.com
        Regression: No

Created attachment 288939
  --> https://bugzilla.kernel.org/attachment.cgi?id=288939&action=edit
lspci output of Lenovo 14w notebook with stoney gpu

Hello,

I do have some issues running a Lenovo 14w notebook in a multi monitor setup.
The displays are connected as followed:

[Lenovo 14w]--(USB-C)-->[Dell U2719DC]--(Display Port)-->[Some other display]

The second display is not connected directly to the notebook. This display is
connected to the monitor output of the Dell display. The Dell display is
configured to use MST and this setup was successfully validated with a Windows
10 installation.

When I plug the Dell 2719DC with the daisy chained monitor via USB-C to the
notebook, the screens are staying black and I get crash of the amdgpu driver in
dmesg. Kernel logs (5.4.28 and 5.4.36) are attached.

My system is currently based on kernel 5.4.28. But I did checked also the
latest kernel version in the 5.4 LTS tree which was 5.4.36. The same error is
reproducable under Ubuntu 20.04 which is based on kernel 5.4.0.

If MST is disabled in the Dell 2719DC, it works as expected. My intenal
notebook screen is expanded with the USB-C connected Dell U2719DC. And the
third monitor is in clone mode with the Dell U2719DC.

Thank you for reading and kind regards,
Johannes Braun

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