USB-C connection from Lenovo X1 Carbon 7th gen to 4K monitor: signal repeatedly dropped
I've attempted to connect my lenovo X1 Carbon (7th gen) to 2 monitors (at different times) via USB-C altmode:
- An LG Ultrafine 5K (running in 4K mode - the 5K mode isn't supported or recognised yet)
- A HP Z27 4K
At first glance, both work well. The resolution is detected and the image appears.
However, at random intervals (usually ~3-4 times per hour) all devices connected via the usb-c port (the monitor on alt mode, and any downstream USB ports plugged into the monitor hubs) disconnect and reconnect. About 4-5 seconds later everything reconnects and continues working.
I can see a few people around the Internet talking about similar issues with usb-c and thunderbolt docks. This unanswered stack exchange question about the external monitor disconnecting under load also sounds very similar: https://unix.stackexchange.com/questions/505729/external-display-briefly-turns-off-under-load
Although most disconnections are random, I can reliably trigger it by turning on screen sharing in a zoom call.
Some details of my system:
$ uname -m x86_64 $ uname -r 5.4.0-2-amd64 $ cat /etc/os-release | head -n 3 PRETTY_NAME="Debian GNU/Linux bullseye/sid" NAME="Debian GNU/Linux" ID=debian
Here's the output from drm_info: drm_info.txt
I haven't tried usb-tip, mostly because it's been 10 years since I compiled a kernel and I haven't had time to get up to speed. However my colleague with an identical laptop is having the same issue, and he reports that it also happens on 5.5-rc5.
Here's a full dmesg from boot until after one of the disconnections, with
drm.debug=0x1e log_buf_len=1M enabled: syslog-usb-disconnect.log
The disconnect and reconnect is around lines 38114-39000. At face value it looks like a cable was unplugged, but there were no physical changes to the laptop cables or ports in this period.
Let me know if I can provide any extra details!