Hi! Thx for reporting your problem!

On 31.03.24 07:59, Andrei Gaponenko wrote:

I noticed a regression with the mailine kernel pre-compiled by EPEL.

I have just tried linux-6.9-rc1.tar.gz from kernel.org, and it still misbehaves.

The default setup: a laptop is connected to a dock, Dell WD22TB4, via a USB-C cable. The dock is connected to an external monitor via a Display Port cable. With a "good" kernel everything works. With a "broken" kernel, the external monitor is still correctly identified by the system, and is shown as enabled in plasma systemsettings. The system also behaves like the monitor is working, for example, one can move the mouse pointer off the laptop screen. However the external monitor screen stays black, and it eventually goes to sleep.

Everything worked with EPEL mainline kernels up to and including kernel-ml-6.7.9-1.el9.elrepo.x86_64

The breakage is observed in

kernel-ml-6.8.1-1.el9.elrepo.x86_64 kernel-ml-6.8.2-1.el9.elrepo.x86_64 linux-6.9-rc1.tar.gz from kernel.org (with olddefconfig)

Other tests: using an HDMI cable instead of the Display Port cable between the monitor and the dock does not change things, black screen with the newer kernels.

Using a small HDMI-to-USB-C adapter instead of the dock results in a working system, even with the newer kernels. So the breakage appears to be specific to the Dell WD22TB4 dock.

Does you laptop offer a HDMI or DP connector? Have you tried if that that works any better? If it does not, then the DRM developers might be willing to look into this.

Anyway: could you try to bisect the problem as described in https://docs.kernel.org/admin-guide/verify-bugs-and-bisect-regressions.html

I strongly suspect that this will be needed to get this resolved: this could be caused by various subsystems, so no developer might be willing to look into this without a bisection result. :-/

Ciao, Thorsten

Operating System: AlmaLinux 9.3 (Shamrock Pampas Cat)

uname -mi: x86_64 x86_64

Laptop: Dell Precision 5470/02RK6V

lsusb |grep dock Bus 003 Device 007: ID 413c:b06e Dell Computer Corp. Dell dock Bus 003 Device 008: ID 413c:b06f Dell Computer Corp. Dell dock Bus 003 Device 006: ID 0bda:5413 Realtek Semiconductor Corp. Dell dock Bus 003 Device 005: ID 0bda:5487 Realtek Semiconductor Corp. Dell dock Bus 002 Device 004: ID 0bda:0413 Realtek Semiconductor Corp. Dell dock Bus 002 Device 003: ID 0bda:0487 Realtek Semiconductor Corp. Dell dock

dmesg and kernel config are attached to https://bugzilla.kernel.org/show_bug.cgi?id=218663

#regzbot introduced: v6.7.9..v6.8.1

Andrei