External Screen detected and initialized but disabled after KDE startup (TB4)

[Cefdinir71]

Hello,
I constantly run into this issue with my Dell 7490 Notebook with latest d-u siduction installed. Same dockingstation connected to my company notebook (Dell NB also, but TB4 connector, Windows 10 installed) does not show this issue.

HW-Setup
- Notebook Dell Latitude 7490 /w TB3 port.
- Dell WD22TB4 docking station (yes I know this is TB4 and my NB has TB3 but this is never an issue and works just fine) plugged into Notebook TB3 port.
- external Dell 30'' screen, connected to docking station via display port.
- external Dell keyboard, external Dell mouse, both connected to WD22TB4 docking station.
- Notebook and dockingstation have latest BIOS/Firmware installed.
- Power Supply connected to dockingstation. Power output is fully sufficient to feed Docking Station and Notebook.
- All devices have their power connected to power extention cord /w separate on/off switch.
- Power extension switch set to OFF position. No device in standby mode. NB fully run down, no hibernation, no suspend mode.
- Dell Notebook lid closed.

SW Settings:
- KDE power settings: Do nothing when notebook screen is opened/closed. Screen set to external screen, no internal screen should be used.

ACTION
(1) Set power cord extension switch to ON.

OBSERVED BEHAVIOUR
(1) Power Supply connector shows blue light enabled,
(2) Docking station WD22TB4 energizes TB4 connector plug,
(3) external Dell screen detected and energized (blue LED activated),
(4) Dell notebook begins boot sequence.
(5) external Dell screen shows DELL logo, grub screen, grub logo, booting sequence continues.
(6) BUG: When external Dell screen should show KDE desktop: external screen is disabled to power save mode.

==> Booting has worked just fine until desktop should be visible, then screen is disabled and black screen is shown.
==> I have to open Notebook lid now. If I press power button of notebook it enables internal notebook screen and shows boot log messages for powering off sequence. I have to reboot /w notebook lid opened during boot. Then external screen shows KDE desktop and lid can be closed again.

EXPECTED BEHAVIOUR:
(1) After switching external power cord switch to ON, docking station gets energized, notebook TB port gets energized, notebook boots into KDE and external screen shows KDE desktop.

Workaround:
- Have notebook lid opened during boot.
- Wait for boot sequence completed and notebook screen getting disabled, external screen shows KDE desktop.
- Close notebook lid (KDE power settings for Notebook set to do nothing when lid closed).

I do not think that this is a boot menu setting of notebook as external screen does work OK. This has got to be some kind of display driver, thunderbolt driver, KDE issue. There is no reason why external screen is disabled again right when desktop should be shown.

Thanks for any hint here.
Cefdinir71.

[unklarer]

I did the same thing these days and found that it's not that easy.

My experience is to make the initial settings mandatory on the laptop. The external Monitor should be plugged in, but not turned on (stand-bay).

Then shut down the laptop and close the lid.
Restart the system via the docking.

My setup:
-ThinkPad 500 and docking station
-siduction lxde (installed July 2021)
-27' monitor HP
-the TP/Dock is on the right and the 27' on the left   

[Cefdinir71]

I think I have found a reasonable workaround.

Instead of fully closing down my notebook after using it I simply use standby-modus. After reconnecting Thunderbold connector that already has power the notebook is started within few seconds, skipping lengthy boot process and omitting also endless lag with recoginizing external screen. It simply shows where I left. It draws a little battery power though.

Regards.