Created attachment 288939 [details]
5.4.28: 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