[REGRESSION] external monitor+Dell dock in 6.8

[Linux regression tracking (Thorsten Leemhuis)]

[Adding a few folks and list while dropping the stable list, as this is
unrelated to it]

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.

Just a quick heads up to ensure people are aware of it:

Imre Deak, turns out this is caused by a patch of yours: 55eaef16417448
("drm/i915/dp_mst: Handle the Synaptics HBlank expansion quirk"). Andrei
Gaponenko meanwhile filed a ticket about it here:

https://gitlab.freedesktop.org/drm/intel/-/issues/10637

Ciao, Thorsten

> 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.
> 
> 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

P.S.:

#regzbot duplicate: https://bugzilla.kernel.org/show_bug.cgi?id=218663
#regzbot duplicate: https://gitlab.freedesktop.org/drm/intel/-/issues/10637
#regzbot title: drm/i915/dp_mst: external monitor on Dell dock broke