[Bug 109675] New: Screens reorganise, failed to enable link training errors in dmesg about 60s after plugging in dock

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109675

            Bug ID: 109675
           Summary: Screens reorganise, failed to enable link training
                    errors in dmesg about 60s after plugging in dock
           Product: DRI
           Version: XOrg git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: shaun at tigera.io
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

I have a Dell Precision 5530 and a Dell TB16 dock.  Either when I first log in
with dock already connected, or when I plug in the dock with external screen
connected over (mini) display port, initially, within about a second the screen
fires up and works as expected with the correct screen layout as previously
configured.  Then, after about 60s of normal behaviour, the screens suddenly
reorganise 2-3 times, with the displays swapping, then showing garbage (half a
screen with black across the other half, magnified) then eventually they
usually settle down to the correct orientation again.  This dance takes about
60s.

At the same time as the screen re-org, I see the following errors in dmesg and
my USB devices attached to the dock sometimes disconnect at that time too:

[  110.409017] [drm:intel_dp_start_link_train [i915]] *ERROR* failed to enable
link training
[  110.678752] [drm:intel_mst_pre_enable_dp [i915]] *ERROR* failed to allocate
vcpi
[  113.561585] [drm:intel_dp_start_link_train [i915]] *ERROR* failed to enable
link training
[  113.829922] [drm:intel_mst_pre_enable_dp [i915]] *ERROR* failed to allocate
vcpi


I'm on Ubuntu, using UKUU to install the mainline kernel.  Most recent
available at time of writing is 4.20.10, behaviour seems consistent with
4.20.x.  Earlier versions had other issues with this dock.

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