[Bug 107546] Screen is frozen on second connection of DP MST dock

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107546

--- Comment #22 from Chris Hobbs <chris at rx14.co.uk> ---
I also have this bug on my Thinkpad 13 with a Onelink+ dock which contains a
displayport MST adapter. I have two screens connected directly over
displayport.

This issue only started happening recently. I will attempt to downgrade my
kernel until I can no longer reproduce. I am currently running
4.18.9-arch1-1-ARCH.

Starting up with the dock connected or disconnected works fine, and so does
disconnecting the dock.

Connecting the dock the first time after starting up with the dock disconnected
works, any further connection attempt fails.

Disconnecting the dock when the display is frozen rectifies the situation, and
the machine can be rebooted normally to restore display. Restarting X11 doesn't
help, it has to be a reboot.

One interesting note is that if you disconnect the dock, then don't issue any
more xrandr commands to disable the now-disconnected displays, you can plug the
dock back in, and the issue doesn't reproduce. The issue only reproduces if you
disable the disconnected displays using xrandr before plugging the dock back
in. The external displays do not have to be enabled in xrandr to freeze the
display.

And in fact, the "frozen screen" on the laptop is actually not frozen, it just
only updates every 5 or so seconds. There's a lot of flickering on the laptop
display when plugging in the dock. Unplugging the dock always restores.

On unplugging, nothing appears in dmesg.

When disabling the unplugged outputs in xrandr, this appears in dmesg:

[ 2037.023131] [drm:intel_dp_start_link_train [i915]] *ERROR* failed to enable
link training
[ 2037.291632] [drm:intel_encoders_pre_enable.isra.63 [i915]] *ERROR* failed to
allocate vcpi


When the dock is plugged back in, this appears in dmesg many times:

[ 2143.988849] [drm:intel_ddi_prepare_link_retrain [i915]] *ERROR* Timeout
waiting for DDI BUF C idle bit

the dmesg messages stop as soon as the dock is unplugged, however the laptop
display takes a few seconds to recover.

Hope this info helps.

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