DisplayPort over USB-C not working after release update

[Geri Joskowicz]

After (automated) update from 5.8.0-63 to 5.11.0.-25 the displayport over usb-c (Thinkpad e15gen2 i5-1135G7 / GeForce MX450/PCIe/SSE2) is not working properly.
Revert to 5.8.0-63 resolves the problem.
The problem is independent of nvdia-drivers (tried 470, 460 and intel only drivers). Same Monitors connected over HDMI work properly. Problem is limited to displayport over usb-c.

Problem symptoms: Monitor atttached over displayport allows only VGA resolution(1024 * 768) and
flickers (on/off periodically).

no special error messages found in dmesg except for abundance of
"i915 0000:00:02.0: [drm] *ERROR* failed to enable link training"

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubuntu-release-upgrader-core 1:20.04.35
ProcVersionSignature: Ubuntu 5.11.0-25.27~20.04.1-generic 5.11.22
Uname: Linux 5.11.0-25-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu27.18
Architecture: amd64
CasperMD5CheckResult: skip
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Sun Aug 8 09:12:10 2021
InstallationDate: Installed on 2021-06-14 (54 days ago)
InstallationMedia: Ubuntu 20.04.2.0 LTS "Focal Fossa" - Release amd64 (20210209.1)
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_IL:en
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_IL
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
Symptom: release-upgrade
UpgradeStatus: No upgrade log present (probably fresh install)
VarLogDistupgradeTermlog:

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[AaronMa (mapengyu)]

Probably it's duplicated bug of #1938999

[Geri Joskowicz (gerijosko)]

Referring to bug #1938999

It seems that the underlying problem is the same,
However, please be aware that Thomas (Bug 1938999) worked on Thunderbolt3 DP and reported:
"Without the dock and one external display it is okay, ..."

whereas the Thinkpad e15 (bug 1939222) has USB-C GEN1 and DP alt mode only.
The E15 fails with a single external display - (attached via usb-c/dp adapter).

The same applies to your test on a T590: T590 has usb-c gen2 / Thunderbolt3 and a second usb-c gen1
Could that be the reason why you can't reproduce the issue on T590 ?

[AaronMa (mapengyu)]

Could you try 5.13 kernel too?
https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.13/amd64/

[Geri Joskowicz (gerijosko)]

Trying, but I'm stuck with the libc6 (>= 2.33) dependency.
Install of 5.13 fails.
Sorry

[Geri Joskowicz (gerijosko)]

Got 5.13 to boot - with nvidia removed (running nouveau)
Exactly the same symptoms as in 5.11: on/off flicker / only VGA resolution.
DP over usb-c not working correctly
I attached the dmesg output - there is a nouveau error message at the end.