eGPU setup - internal laptop display not usable

[Vlad Bejenaru]

I have the following configuration:
- Xubuntu 20.04 updated to kernel 5.4.0-47
- Lenovo Thinkpad T480 with Intel i5-7300U and Intel HD Graphics 620
- eGPU via Thunderbolt 3: HP Omen Accelelerator + Nvidia GFX1070
- 2 external monitors connected to the eGPU: 1 DisplayPort + 1 DVI

Before the upgrade to kernel 5.4.0-47 I could use all 3 monitors (1 internal + 2 external).

Since the upgrade to kernel 5.4.0-47 the internal monitor is not usable anymore. It is not displayed by xrandr --query and remains blank with a small background luminescence

Expected to happen: to be able to use all 3 available monitors (2 external + 1 internal)
What happens: only the external monitors (the one connected directly to eGPU) are available, the internal monitor remains black but with backlight.

lsb_release -rd
Description: Ubuntu 20.04.1 LTS
Release: 20.04

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.4.0-47-generic 5.4.0-47.51
ProcVersionSignature: Ubuntu 5.4.0-47.51-generic 5.4.55
Uname: Linux 5.4.0-47-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu27.8
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: vlad 1868 F.... pulseaudio
 /dev/snd/controlC0: vlad 1868 F.... pulseaudio
CasperMD5CheckResult: skip
CurrentDesktop: XFCE
Date: Thu Sep 17 09:18:19 2020
InstallationDate: Installed on 2020-08-29 (18 days ago)
InstallationMedia: Xubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
MachineType: LENOVO 20L6S8LU1W
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.4.0-47-generic root=UUID=3792990b-6d8f-4e09-80fa-4fa1a59be11f ro quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-5.4.0-47-generic N/A
 linux-backports-modules-5.4.0-47-generic N/A
 linux-firmware 1.187.3
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 06/02/2020
dmi.bios.vendor: LENOVO
dmi.bios.version: N24ET59W (1.34 )
dmi.board.asset.tag: Not Available
dmi.board.name: 20L6S8LU1W
dmi.board.vendor: LENOVO
dmi.board.version: SDK0J40697 WIN
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: None
dmi.modalias: dmi:bvnLENOVO:bvrN24ET59W(1.34):bd06/02/2020:svnLENOVO:pn20L6S8LU1W:pvrThinkPadT480:rvnLENOVO:rn20L6S8LU1W:rvrSDK0J40697WIN:cvnLENOVO:ct10:cvrNone:
dmi.product.family: ThinkPad T480
dmi.product.name: 20L6S8LU1W
dmi.product.sku: LENOVO_MT_20L6_BU_Think_FM_ThinkPad T480
dmi.product.version: ThinkPad T480
dmi.sys.vendor: LENOVO

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This change was made by a bot.

[Vlad Bejenaru (vladbejenaru)]

I can confirm the same bug also for 5.4.0-45 and for 5.4.0-48 and also a workaround. In kernel 5.4.0-45 it is happening only one out of 3-4 times directly on boot. In all the other 2 kernels (5.4.0-47 and 5.4.0-48) it is happening on each cold boot.

Workaround: after first cold boot from the login screen I restart the computer. After restart the laptop display is available. If I shut down and power on I still have the problem.