linux-kernel - thinkpad x1 carbon display flickering after update to 5.12. good on 5.11.x (i915)

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Date:   Fri, 14 May 2021 10:24:26 +0200
From:   Thomas Stein <himbeere@...ne-oma.de>
To:     linux-kernel@...r.kernel.org
Subject: thinkpad x1 carbon display flickering after update to 5.12. good on
 5.11.x (i915)

Hello Devs.

After upgrading to linux 5.12 the display on my X1 Carbon Gen 2 starts 
to flicker. Well actually it seems to turn off and on again and again. 
Here a link to a video a person posted who has the same issue as me 
obviousely. 
https://linuxove.com/thinkpad-x1-carbon-gen-3-display-flickering-on-linux-kernel-5-12/

This happens without having Xorg running too. So it can't be related to 
Xorg. The kernel boots and after a few seconds, the kernel messages 
scoll through, the flickering starts. Nothing special in dmesg.

dmesg:

himbeere@...her ~ $ dmesg | grep i915
[    0.713595] i915 0000:00:02.0: vgaarb: deactivate vga console
[    0.720280] i915 0000:00:02.0: vgaarb: changed VGA decodes: 
olddecodes=io+mem,decodes=io+mem:owns=io+mem
[    0.741494] i915 0000:00:02.0: [drm] Panel advertises DPCD backlight 
support, but VBT disagrees. If your backlight controls don't work try 
booting with i915.enable_dpcd_backlight=1. If your machine needs this, 
please file a _new_ bug report on drm/i915, see 
https://gitlab.freedesktop.org/drm/intel/-/wikis/How-to-file-i915-bugs 
for details.
[    1.864837] [drm] Initialized i915 1.6.0 20201103 for 0000:00:02.0 on 
minor 0
[    1.875907] fbcon: i915drmfb (fb0) is primary device
[    3.158255] i915 0000:00:02.0: [drm] fb0: i915drmfb frame buffer 
device
himbeere@...her ~ $

Downgrading to 5.11 solves the issue for me. Any ideas?

cheers, t.