Created attachment 143493 [details]
I am using a Dell XPS 13 (9370) connected to a Caldigit TS3 Plus thunderbolt dock. On this dock I have two monitors connected. One is connected to the display port of the dock, the second one is connected to an USB-C Thunderbolt port using an USB-C to mini DP adapter.
The second monitor is only detected, when I _first_ plug in the adapter and _then_ plug in the the cable to the adapter. This also only works when the system has booted _and_ I am logged in. I already disabled thunderbolt security completely in UEFI. Once the monitor has been detected it is also working during boot, when I restart the system. This also appears when directly plugging in the adapter to a Thunderbolt port of the laptop.
I can reproduce the issue also with latest DRM-tip kernel
I Reported this bug already to Ubuntu kernel: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1817070
Repoerter, Can you please verify the issue with drmtip (https://cgit.freedesktop.org/drm-tip) and kernel parameters drm.debug=0x1e log_buf_len=4M, and if the problem persists attach the full dmesg from boot.