[Bug 1901215] Re: Cannot boot with thunderbolt dock connected before kernel loads

FWIW I am seeing this also with my Lenovo X1 Carbon 6th when docked to
my Thinkpad Ultra Docking Station (that has 2 external monitors
connected to it). This booted fine on focal but after upgrading to
Groovy (or doing a fresh install) the boot hangs as soon as the plymouth
splash screen tries to display. Setting nospash in /etc/default/grub
(GRUB_CMDLINE_LINUX_DEFAULT) works around this for now by disabling the
splash screen.

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Title:
Cannot boot with thunderbolt dock connected before kernel loads

Status in linux package in Ubuntu:
Confirmed

Bug description:
Dell XPS 9650 with a TB16 thunderbolt dock. 2 external displays
through the dock (HDMI and VGA). My system uses graphical boot via
plymouth. Dell logo remains on screen while ubuntu loads into gdm3
(when it is booting normally). I'm using LUKS.

This is a regression from focal and kernel 5.4.

If I boot the laptop with the thunderbolt dock connected, the system
will get past the Dell logo, go to a black screen and remain there.
The screen is powered up as I can see some light on the edges. It
won't boot up or respond to any keys.

After force-shutdown via power key long press, on the next boot the
grub menu will appear. The system will boot normally then (with the
dock still connected).

If I boot the system with the dock disconnected, it will correctly go
into disk encryption password prompt. If at that point I connect the
dock and wait without entering the password, the system will correctly
set up the dock: the displays lit up and the mouse and keyboard
plugged into it become active. The system boots normally.

I'm trying to bisect in which kernel version this happened. I'll put
results in a comment.

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: linux-image-generic 5.8.0.25.30
ProcVersionSignature: Ubuntu 5.8.0-25.26-generic 5.8.14
Uname: Linux 5.8.0-25-generic x86_64
ApportVersion: 2.20.11-0ubuntu50
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC1: luis 3332 F.... pulseaudio
/dev/snd/controlC0: luis 3332 F.... pulseaudio
CasperMD5CheckResult: skip
Date: Fri Oct 23 16:27:30 2020
InstallationDate: Installed on 2019-08-17 (432 days ago)
InstallationMedia: Ubuntu 19.04 "Disco Dingo" - Release amd64 (20190416)
MachineType: Dell Inc. XPS 15 9560
ProcEnviron:
LANGUAGE=en_GB:en
TERM=xterm-256color
PATH=(custom, no user)
LANG=en_GB.UTF-8
SHELL=/bin/bash
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-5.8.0-25-generic root=/dev/mapper/vglinux-root ro quiet splash
PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No PulseAudio daemon running, or not running as session daemon.
RelatedPackageVersions:
linux-restricted-modules-5.8.0-25-generic N/A
linux-backports-modules-5.8.0-25-generic N/A
linux-firmware 1.190
SourcePackage: linux
UpgradeStatus: Upgraded to groovy on 2020-10-09 (13 days ago)
dmi.bios.date: 11/17/2019
dmi.bios.release: 1.18
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 1.18.0
dmi.board.name: 05FFDN
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 10
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvr1.18.0:bd11/17/2019:br1.18:svnDellInc.:pnXPS159560:pvr:rvnDellInc.:rn05FFDN:rvrA00:cvnDellInc.:ct10:cvr:
dmi.product.family: XPS
dmi.product.name: XPS 15 9560
dmi.product.sku: 07BE
dmi.sys.vendor: Dell Inc.

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