[kde] [Bug 448177] New: Thunderbolt dock 4k screen flickering

[Lorenz/Qrly]

https://bugs.kde.org/show_bug.cgi?id=448177

            Bug ID: 448177
           Summary: Thunderbolt dock 4k screen flickering
           Product: kde
           Version: unspecified
          Platform: Gentoo Packages
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: unassigned-bugs at kde.org
          Reporter: me at qrly.wtf
  Target Milestone: ---

Created attachment 145279
  --> https://bugs.kde.org/attachment.cgi?id=145279&action=edit
Wird pixel rendering 4k at 60Hz HDMI

Hello,

first, here is a short video showing the issue:
https://www.youtube.com/watch?v=c2sVZwb5mg0.

Basicly, I've got a 4k monitor connected on my Thinkpad thunderbolt 3 gen 2
Workstation dock:
Monitor: https://www.lg.com/us/monitors/lg-32UK550-B-4k-uhd-led-monitor
Dock:
https://support.lenovo.com/rs/en/solutions/pd500333-thinkpad-thunderbolt-3-workstation-dock-gen-2-overview-and-service-parts

The screen goes black after "changing to many pixels", for example while
fullscreen web browsing, playing a fullscreen video, etc. This only happens
while the monitor is running at 4k. 2k and blow is not an Issue.

This isn't a fix (because I tried it):
- Disabling all other monitors 
- Only plugging the monitor Cable into the Dock
- Using another Thunderbolt dock
- Using other 4k Screens
- Using diffrent cables that I know work
- Using Manjaro KDE, KDE neon, endeavouros KDE, all showing the same behavior

How do I know that this is a Plasma specific issue?
Because the screen is working in Xfce and swaywm at 4k at 60Hz. 
It could also not be one, because same problem like in kde also exsists in dwm
and awesomewm.

Why do I use a docking station?
Because my Laptop (You can find my hardware specs below) only has 1.4b, which
after the official hdmi spec only supports 4k at 30Hz (" 3840×2160 at 24, 25, and
30 Hz", https://www.hdmi.org/spec/hdmi1_4b) while my Displayport version
officially supports 4k at 60Hz. My Laptop doesn't have a Displayport Port.

How do I know that this is a bug only appering when using a docking station?
I tried two diffrent docking stations, both showing the same result. (Maby I
will have the chance to test other laptops in the next days). While my HDMI
version doesn't officially supports 4k at 60Hz, whith my HDMI port on my Laptop I
am able to achive 4k at 60Hz, but with wird rendering(You can find a image showing
how the rendering looks in the attachments), thats why I need displayport. 
But, 4k at 60Hz on HDMI works without the wird black screen that you get when
"changing to many pixels".

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