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Philos

Member

Registered: 2024-10-14

Posts: 2

No external displays detected via USB-C

When pluggin in an external display via the USB-C/Thunderbolt 4 port of my Lenovo T15 Gen2 (Intel Iris Xe, no dedicated GPU), no displays are detected. They are also not detected during boot.
This occurs on both direct USB-C connections to displays with a USB-C port, as well as when using docking stations. I see this behavior also using two different monitors from two different brands (one from Lenovo/ThinkVision, one from Dell). The two cables, one per monitor, have been checked with other laptops and are known to work. The BIOS doesn't contain any explicit "toggle this to enable/disable DP Alt Mode", all vaguely relevant toggles such as "Enable Thunderbolt 4" are enabled, although I did not touch these to begin with and the current configuration has worked for at least a year.

Weirdly enough, I see this behavior on the most recent Linux Kernel 6.11.3.arch1-1, as well as the current LTS Kernel version 6.6.56-1-lts. The change seemingly happened "overnight", meaning without explicitly updating e.g. the BIOS. I updated the BIOS to the newest version, but to no avail. Similar story with fwupdmgr: I did not run any explicit updates prior to this issue appearing, and updating all relevant components (including the docking station) does not change this behavior.

I am not using dual-boot. For the desktop environment I use KDE Plasma 6 Wayland, although the X11 variant also shows the same behavior.

Curiously, HDMI _does_ work.

I have attached the output of several relevant logging facilities.

- full dmesg
- full journalctl
- journalctl events on USB-C replug
- udevadm monitor output on USB-C replug
- edid-decode for all in  `/sys/class/drm/card*`

At this point, I am somewhat lost with how to continue. I would highly appreciate any input! Also please let me know if I can provide you with any other information.

gromit

Administrator

From: Germany

Registered: 2024-02-10

Posts: 1,519

Website

Re: No external displays detected via USB-C

Did you already try if downgrading the kernel does help? I.e. going to one or two versions lower for the linux-lts and linux packages? It could possibly a bad commit that got backported to both stable trees.

Philos

Member

Registered: 2024-10-14

Posts: 2

Re: No external displays detected via USB-C

So this was an interesting one. @gromit While I did not try to downgrade the kernel, I did try a live boot of a standard Ubuntu as well as a Windows 11 PE, both of which curiously did not recognize the external displays, suggesting a bad port.
Simultaneously, I started to notice that I could no longer charge my battery, neither with a USB-C hub nor with a dedicated power brick. Weirdly enough, the OS (all of the ones I tried) reported the battery to be charging, even when unplugging all cables. Additionally, the small amber USB-C LED remained on even on shutdown.

At some point, the battery ran out of charge, which probably reset some parts of the USB-C circuit. After that shutdown, the battery charged again and external monitors were recognized again via USB-C.

TL;DR: Fully draining the battery presumably reset some components and restored external displays via USB-C.