Screens reorganise, failed to enable link training errors in dmesg about 60s after plugging in dock

Submitted by Shaun

Assigned to Intel GFX Bugs mailing list

Link to original bug (#109675)

Description

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.