Created attachment 190546 [details] Photo showing both screen the 4k being distorted SUMMARY My external (second) 4k Thunderbolt screen shows a login screen that is scaled by 2x vertically (only). After login everything is fine again, it happens only at login. I see this both with Ubuntu 16.04 (sddm) and KDE Linux (plasma-login). Nate pointed me here STEPS TO REPRODUCE Just let the machine boot to the GUI login and observe the second screen. OBSERVED RESULT While the login screen is correct on the built-in screen it is distorted on the external screen. Both with Ubuntu and KDE-Linux despite them using different login-managers. EXPECTED RESULT The screen on the external display not being distorted. SOFTWARE/OS VERSIONS Operating System: KDE Linux 2026-03-10 KDE Plasma Version: 6.6.80 KDE Frameworks Version: 6.25.0 Qt Version: 6.10.2 Kernel Version: 6.19.6-zen1-1-zen (64-bit) Graphics Platform: Wayland Processors: 12 × 13th Gen Intel® Core™ i7-1365U Memory: 32 GiB of RAM (31.0 GiB usable) Graphics Processor: Intel® Iris® Xe Graphics Manufacturer: LENOVO Product Name: 21HNS00100 System Version: ThinkPad X1 Carbon Gen 11 ADDITIONAL INFORMATION
Created attachment 190547 [details] Output from drm_info while login screen being shown
Created attachment 190548 [details] Output from drm_info while after login with normal desktop (all is fine now)
Created attachment 190549 [details] Output from drm_info during login session but while switched to VT (in case this might be helpful)
Please attach the edid of the display. You can get it with > cat /sys/class/drm/card1/card1-DP-1/edid > edid.bin (the connector name might need adjusting)
Created attachment 190568 [details] Binary EDID output As proposed here is the EDIT output. Its the only non-empty file among all cards available (other then the internal eDP connector). Hope its the right one.
Created attachment 190569 [details] EDID output from KDE Info Center as text
Just provided the requested binary output but also the Text output from the KDE Info Center app. Hope this helps finding the issue.
Hmm, our autotest passes with that, it chooses 2160p by default. From a tty, please do > sudo systemctl stop plasmalogin (this will stop any existing sessions), move > /var/lib/plasmalogin/.config/kwinoutputconfig.json somewhere else, and reboot. Is the resolution still wrong after that?
Created attachment 190590 [details] The old file
Created attachment 190591 [details] The new kwinoutputconfig.json file after removal and reboot
Thanks a lot, this did the trick! I have included the old and new files as attachments in case this might be useful. And indeed the old one had the 4kx1080 listed. Now the question is, how on earth did it come up with this. And maybe more important, can we avoid this happening again to me or others. Can such cases be detected and ignored? Does sddm have a similar file that I should delete? Because I see the same problem there under Kubuntu 26.04.
Just got the change to test it and the problem is also gone on Kubuntu 26.04 (shared home dir).
> Now the question is, how on earth did it come up with this. And maybe more important, can we avoid this happening again to me or others. There was a bug in the default mode selection, but it was already fixed and backported to 6.5.6 and 6.6.0. Presumably your system simply chose and saved the default mode before it was fixed. > Can such cases be detected and ignored? We unfortunately don't have a flag for whether or not the mode was selected automatically or by you. I (intentionally) set up the output configuration stuff so that we never change your settings automatically, because output settings are a bit dangerous. In the long run, our goal is to automatically sync the user display settings to plasma login, so it will be papered over then. > Does sddm have a similar file that I should delete? Because I see the same problem there under Kubuntu 26.04. Yeah, it should be at /var/lib/sddm/.config/kwinoutputconfig.json
Thanks a lot for the support. It s much appreciated!