Bug 508872

Summary:	Display keeps getting engaged as 30-bit when it should be 24-bit
Product:	[Plasma] kwin	Reporter:	EntranceJew
Component:	platform-drm	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED UPSTREAM
Severity:	normal	CC:	EntranceJew, kde, xaver.hugl
Priority:	NOR
Version First Reported In:	unspecified
Target Milestone:	---
Platform:	NixOS
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:
Attachments:	monitor OSD showing color settings

Description EntranceJew 2025-08-28 20:25:42 UTC

Created attachment 184535 [details]
monitor OSD showing color settings

SUMMARY
KWin keeps engaging my monitors at 30-bit color instead of 24-bit color, causing graphical instability. It happens on the DRM drivers, and the open drivers.

STEPS TO REPRODUCE
1. set KWIN_DRM_PREFER_COLOR_DEPTH=24
2. that does not occur

OBSERVED RESULT
monitor shows 30-bit color, unlike on Windows

EXPECTED RESULT
monitor shows 24-bit color like on Windows

SOFTWARE/OS VERSIONS
Operating System: NixOS 25.05
KDE Plasma Version: 6.3.6
KDE Frameworks Version: 6.14.0
Qt Version: 6.9.1
Kernel Version: 6.12.43 (64-bit)
Graphics Platform: Wayland
Processors: 16 × 11th Gen Intel® Core™ i9-11900K @ 3.50GHz
Memory: 125.6 GiB of RAM
Graphics Processor: NVIDIA GeForce RTX 3070 Ti

ADDITIONAL INFORMATION
https://gist.github.com/EntranceJew/006b8d2253aec9e2ba5d12e0a1e90cbf
https://github.com/entrancejew/dot-nix

Comment 1 Zamundaaa 2025-08-29 10:20:53 UTC

NVidia doesn't support the "max bpc" property yet, so it's impossible to limit bit depth. Please report this at https://forums.developer.nvidia.com/c/gpu-graphics/linux

Comment 2 EntranceJew 2025-08-29 16:56:53 UTC

(In reply to Zamundaaa from comment #1)
> NVidia doesn't support the "max bpc" property yet, so it's impossible to
> limit bit depth. Please report this at
> https://forums.developer.nvidia.com/c/gpu-graphics/linux

Just making sure I'm understanding this correctly, as I had noted that it was an issue with both:
- the DRM driver
- the open (Nouveau?) drivers

Is NVidia's hardware controlling this whole pipeline, directly from interrogating my display capabilities down to pushing the image, bypassing both the DRM and Nouveau drivers in the process?
Am I going to be reporting a microcode bug on the hardware itself?
Does NVidia also control the Nouveau drivers, and will they update those as well?

In order to make an account on that forum it says I have to have a job?
Should I put KDE as my employer?

Apologies for any misunderstandings, I just want to make sure I am being accurate with what I am reporting.

Comment 3 Zamundaaa 2025-08-30 12:45:03 UTC

I don't know how exactly the driver implements things under the hood, and it doesn't matter. Where to fix it is something NVidia has to know.

> Does NVidia also control the Nouveau drivers, and will they update those as well?
They do work on Nouveau.

> In order to make an account on that forum it says I have to have a job? Should I put KDE as my employer?
No.

You can also report it at https://github.com/NVIDIA/open-gpu-kernel-modules/issues if that's easier.