ThinkPad E14 Gen 2 with i915 (Intel Xe Graphics): external 4k monitor flickering
My laptop: ThinkPad Lenovo E14 Gen 2 Type Number: 20TA-000DGE CPU: 11th Gen Intel i7-1165G7 (8) @ 4.700GHz (Rocket Lake) GPU: Intel Device 9a49 / i915 Thunderbolt: v4 (only one; needed for power and external monitor) HDMI
My monitor: LG 27UK850/BK85U 4k (3840*2160)
My external USB-C hub: DockTeck (find with headline "USB C Hub, Dockteck 7-in-1 Dock HyperExtended USB C Ethernet Adapter, 4K 60Hz HDMI, LAN RJ45, 100W PD, 2 USB-3.0, SD/microSD, für MacBook Pro/Air, iPad Pro/Air/Mini 6, Surface Pro 7, XPS 13")
Behavior on windows 10: HDMI and the USB-c hub provide both a stable display on my monitor, with 4k and 60hz (hint: on windows, HDMI did only work @60hz after BIOS update).
My system: Linux Mint 20.2, Kernel 5.14 OEM
My Problem: on the USB-C hub: 4k @ 60hz is running for a short time (until first refreshes on the external monitor come in); then: the 4k display flickers (1-3 second black screen; after some of these flushes the external monitor turns black)
A longer problem description with multiple different configurations tried out: https://unix.stackexchange.com/questions/677892/linux-mint-20-2-4k-monitor-with-i915-intel-xe-graphics
For debugging I started my system (Linux Mint 20.2, Kernel 5.14 OEM; external Monitor on the USB-C hub, HDMI cable from USB-C hub to the monitor connected at power on) with passing "drm.debug=0xe log_buf_len=4M" to the kernel cmdline (as suggested from @vsyrjala ). See attached log-file: dmesg_all_2021-12-16.log
\cc @jensens @binarious