Can't change screen resolutions in Plasma

[vs49688]

Describe the bug

Can't change screen resolutions in Plasma.

Steps To Reproduce

Steps to reproduce the behavior:

1. Install NixOS with Plasma
2. Attempt to change screen resolution

Expected behavior

The screen resolution changes.

Additional context

This happens on multiple machines, both laptops, on the Wayland session. When I open systemsettings and click on Display & Monitor, it spits out kf.coreaddons: "Could not load plugin from kcm_kscreen: The shared library was not found." in console, which makes me think it's something related to NixOS and pathing.

Suspiciously, both $ kscreen-console config and $ kscreen-console outputs are empty, and $ kscreen-console monitor reports nothing.

After changing the resolution, the refresh rate field in the GUI changes to something nonsensical, e.g.:

• 3546x2160 - 60Hz (original, good)
• 2560x1600 - 728501Hz
• 1920x1200 - 1293352Hz

This might be related to https://bugs.kde.org/show_bug.cgi?id=455477, but I'm not getting a crash.

I'm prepared to submit this upstream, if it's a non-NixOS issue.

Logs

systemsettings.log

Notify maintainers

@ttuegel @nyanloutre @peterhoeg

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

• system: "x86_64-linux"
• host os: Linux 5.17.15, NixOS, 22.11 (Raccoon), 22.11.20220618.e0a4226
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.9.1
• channels(root): "nixos"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

[peterhoeg]

I just tried and I can change the resolution but I also get the message that you do:

$ systemsettings
kf.service.services: The desktop entry file "/run/current-system/sw/share/applications/kcm_krunnersettings.desktop" has Type= "Application" but no Exec line
kf.service.sycoca: Invalid Service :  "/run/current-system/sw/share/applications/kcm_krunnersettings.desktop"
QQmlEngine::setContextForObject(): Object already has a QQmlContext
qt.qpa.wayland: Wayland does not support QWindow::requestActivate()
kf.coreaddons: "Could not load plugin from kcm_kscreen: The shared library was not found."
QQmlEngine::setContextForObject(): Object already has a QQmlContext
qml: The item SubCategoryPage_QMLTYPE_103(0xe53140) is already in the PageRow
kf.coreaddons: "Could not load plugin from kcm_kscreen: The shared library was not found."

Both $ kscreen-console config and $ kscreen-console outputs give me lots of output.

Could you try to run this:

$ rm $HOME/.cache/systemsettings/qmlcache

And then try again?

[vs49688]

First thing I did when I updated to 5.25. Just tried again, no change.

[peterhoeg]

I have no idea why my mail reply isn't being picked up, so pasting it in here:

You want the good news or the bad news first? Doesn’t matter - it’s both good and bad.

It’s working fine (as mentioned) for me on the desktop but on the laptop, I’m seeing the same as you do - the resolution doesn’t change, although it depends on which resolution I try.

The laptop LCD supports 1080p natively.

• If I try to change to 1600x900, “Display Configuration” tells me it changed, but the screen doesn’t.
• If I try 1280x720, it does change.

I’m thinking this is maybe a hardware issue where the panel simply doesn’t support certain resolutions.

[vs49688]

Could you try it in an X11 session on the laptop? I can change resolutions fine when using X11, I suspect it may be an issue with https://invent.kde.org/plasma/kwin/-/merge_requests/2235.

The panel on one of the laptops only reports 3840x2160 (have checked the EDID) and the integrated HD 530 can't handle it well, so I want to run it lower. X11's fake modes work fine, kwin's fake don't.

EDIT: Same for the other laptop, only reports 3456x2160

[peterhoeg]

Indeed, works fine on X11. Out of curiosity - what’s wrong with running the panel at its native resolution and increasing the scale factor instead?

[vs49688]

I would love to, but the vendor cheaped-out on the integrated GPU - it struggles to drive it at 4k. I've found it s significantly more responsive at 1080p.

[vs49688]

This is fixed on unstable now.

[peterhoeg]

You want the good news or the bad news first? Doesn’t matter - it’s both good and bad. It’s working fine (as mentioned) for me on the desktop *but* on the laptop, I’m seeing the same as you do - the resolution doesn’t change, although it depends on which resolution I try. The laptop LCD supports 1080p natively. If I try to change to 1600x900, “Display Configuration” tells me it changed, but the screen doesn’t. If I try 1280x720, it *does* change. I’m thinking this is maybe a hardware issue where the panel simply doesn’t support certain resolutions.

[vs49688]

Yeah, that does sound like the panel not supporting the mode. Mine only reports 2160p, but supports basically everything, now that "Display Configuration" creates the "fake" modes.

Oddly enough, mine supports 1080p, but it isn't displayed in the drop-down.