https://bugs.kde.org/show_bug.cgi?id=511646
Bug ID: 511646
Summary: KWin Wayland: DRM initialization fails due to absence
of /dev/dri/card0 (caused by nvidia-drm.fbdev=0),
failing to fallback to card1
Classification: Plasma
Product: kwin
Version First 6.5.1
Reported In:
Platform: Neon
OS: Linux
Status: REPORTED
Severity: critical
Priority: NOR
Component: platform-fbdev
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
The core issue is a structural defect in KWin 6.5.1's DRM initialization logic.
It rigidly attempts to access the device file at /dev/dri/card0 and cannot
gracefully handle the absence of this file (an ENOENT error) by automatically
falling back to the only available, valid GPU device, /dev/dri/card1.
Chain of Consequences: Kernel → udev → KWin
The problem is triggered by a seemingly optimal configuration, revealing the
KWin bug:
1. Kernel Optimization (The Trigger)
Action: added the kernel parameter nvidia-drm.fbdev=0 to the GRUB command
line.
Result: this flag instructs the kernel's NVIDIA driver not to register the
legacy VESA/simple framebuffer device.
2. udev Device Management (Correct Action)
Action: as a result of the kernel's decision, the udev device manager never
receives an event to create the device file for the fallback GPU.
Result: the file /dev/dri/card0 is correctly and intentionally absent from
the filesystem. This verifies the system configuration is clean.
3. KWin Failure (The Bug)
Action: KWin begins its initialization and attempts to access the DRM
backend via a hard-coded or strictly ordered search for device files.
Result (The Bug): KWin fails on the non-existent /dev/dri/card0 and aborts
the entire DRM initialization sequence, resulting in the log error:
kwin_wayland_drm: failed to open drm device at "/dev/dri/card0".
some tests:
a) journalctl -b -e --user-unit=plasma-kwin_wayland.service -g "kwin"
kwin_wayland_drm: failed to open drm device at "/dev/dri/card0"
b) ls -l /dev/dri/
total 0
2 root root 100 nov 4 20:06 by-path
1 root video 226, 1 nov 4 20:06 card1
1 root render 226, 128 nov 4 20:06 renderD128
Operating System: KDE neon User Edition
KDE Plasma Version: 6.5.1
KDE Frameworks Version: 6.19.0
Qt Version: 6.9.2
Kernel Version: 6.14.0-35-generic (64-bit)
Graphics Platform: Wayland
Memory: 16 GiB of RAM (15.6 GiB usable)
Graphics Processor: NVIDIA GeForce GT 1030
--
You are receiving this mail because:
You are watching all bug changes.
