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FS#70135 - [linux] HP Thunderbolt Dock G2 unusable with Linux 5.11

Attached to Project: Arch Linux
Opened by Philipp Klein (kleinph) - Tuesday, 23 March 2021, 16:20 GMT
Last edited by Andreas Radke (AndyRTR) - Wednesday, 24 March 2021, 12:47 GMT
Task Type Bug Report
Category Kernel
Status Assigned
Assigned To Jan Alexander Steffens (heftig)
Architecture x86_64
Severity High
Priority Normal
Reported Version
Due in Version Undecided
Due Date Undecided
Percent Complete 0%
Votes 0
Private No



Since kernel version 5.11 my HP Thunderbolt Dock G2 is unusable.
I get no video output on the monitor connected to the dock (via a DisplayPort to HDMI cable). Connected peripherals (mouse, keyboard) also don't work and the input lags a bit.
The log is spammed with "kernel: i915 0000:00:02.0: [drm] *ERROR* Link Training Unsuccessful" messages.

I tried all point releases of Linux 5.11 with no success.
Last working version for me is linux 5.10.16.arch1-1.

Additional info:
* linux 5.11.x
* config and/or log files etc.

Steps to reproduce:

Install a linux 5.11.x package, reboot, connect HP Thunderbolt Dock G2.
This task depends upon

Comment by Philipp Klein (kleinph) - Wednesday, 24 March 2021, 17:57 GMT
I built linux-mainline from AUR (tried both 5.12rc3-1 and 5.12rc4-1) with no success.

I attached dmesg output with drm debug information.

Some additional information:
Device: Lenovo ThinkPad T480s
CPU: Intel Core i7-8550U
GPU: Intel UHD Graphics 620 (KBL GT2)
The kernel is not tainted (`cat /proc/sys/kernel/tainted` returns 0)
Comment by Philipp Klein (kleinph) - Thursday, 01 April 2021, 16:38 GMT
With linux-mainline 5.12.0-rc5-1 the issue is no longer present. I attached a boot log of this kernel with DRM debug information.
Comment by Jan Alexander Steffens (heftig) - Thursday, 01 April 2021, 17:09 GMT
rc5 contains some commits to i915 regarding DisplayPort LTTPRs that seem relevant.
Comment by loqs (loqs) - Friday, 02 April 2021, 07:51 GMT Comment by Philipp Klein (kleinph) - Sunday, 04 April 2021, 13:43 GMT
@loqs I can confirm that the patched kernel your provided fixes the problem.