[Bug 111250] New: i915 external monitor not working in usb-c/thunderbolt dock on X1 gen6

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111250

            Bug ID: 111250
           Summary: i915 external monitor not working in usb-c/thunderbolt
                    dock on X1 gen6
           Product: DRI
           Version: XOrg git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: major
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: tmai at math.upb.de
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 144909
  --> https://bugs.freedesktop.org/attachment.cgi?id=144909&action=edit
dmesg while reproducing the error twice

Hi,

I cannot get external monitors to work on my X1 gen6 on Linux (Ubuntu) when
they are connected over a dock. I tried the official dock from lenovo as well
as an third-party usb-c adapter. The systems immediately freezes if I hotplug
an external monitor or it freezes when I try to configure the external monitor
(which is not enabled in the settings up to this point). It unfreezes when the
cable is disconnected. In some cases booting with the external monitor ended up
at a log-in screen with reduced screen resolution (below full HD).

Kernel: 5.3.0-994-generic
(from here: https://kernel.ubuntu.com/~kernel-ppa/mainline/drm-tip/2019-07-27/)
However, it affects various other kernel versions as well.

OS: Kubuntu 19.04

Machine: Lenovo X1 (Gen6); 20KGS03800

Display connector: HDMI and DP

dmesg is attached (external monitor was connected twice after boot up)

Additional info:

External monitors were working on Kubuntu 18.04 earlier this year. The other
day, I tried the livesystem 18.04.2 which is already affected by the bug.

Please, let me know if I can provide any further information from my end or
point me to any other place where I should report this bug instead.

Thanks to anyone who looks into this.

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