[Bug 2155617] Re: Backlight device disappears and brightness breaks on kernel 6.17.0-23+ (Lenovo Legion 5 Pro, NVIDIA hybrid graphics)

I executed the commands that you provided to add acpi_backlight=native to the kernel command line and updated GRUB accordingly. Results: Kernel 6.17.0-35: No change. The issue remains. Brightness control is still non-functional. The mouse pointer still exhibits rendering artifacts/trailing. Kernel 6.17.0-22: Still works correctly with the same change applied. Brightness control works normally. No pointer artifacts observed. Please let me know if you would like me to collect any additional logs or perform further testing. -- You received this bug notification because you are subscribed to linux in Ubuntu. Matching subscriptions: Bgg, Bmail, Nb https://bugs.launchpad.net/bugs/2155617 Title: Backlight device disappears and brightness breaks on kernel 6.17.0-23+ (Lenovo Legion 5 Pro, NVIDIA hybrid graphics) Status in linux package in Ubuntu: New Bug description: On Ubuntu 24.04.2 LTS running on a Lenovo Legion 5 Pro 16ACH6H (AMD + NVIDIA RTX 3070 hybrid system), brightness control breaks starting from kernel 6.17.0-23-generic and remains broken on all newer kernels up to 6.17.0-35. The issue is fully reproducible. WORKING KERNEL: - 6.17.0-22-generic - Display session: X11 - NVIDIA proprietary driver in use - Backlight device present: /sys/class/backlight/nvidia_0 - Brightness control works normally BROKEN KERNELS: - 6.17.0-23-generic and newer (tested up to 6.17.0-35) - Wayland or X11 both affected - Backlight directory is empty: /sys/class/backlight/ SYMPTOMS: - Brightness stuck at 100% - No backlight device exposed in sysfs - Mouse cursor shows trailing/ghosting artifacts on Wayland - Display rendering instability EXPECTED BEHAVIOR: - /sys/class/backlight/nvidia_0 should be present - Brightness control should function via NVIDIA DRM backlight interface ACTUAL BEHAVIOR: - No backlight device is registered at all in /sys/class/backlight/ - GNOME brightness controls have no effect HARDWARE: - Lenovo Legion 5 Pro 16ACH6H - AMD Ryzen CPU (iGPU present but not used for display in working kernel) - NVIDIA RTX 3070 Mobile (primary display output via nvidia-drm) - NVIDIA proprietary driver active REGRESSION: - Kernel 6.17.0-22 works correctly - 6.17.0-23 introduces regression and all newer kernels inherit it This appears to be a regression in NVIDIA DRM backlight device registration (fbdev / sysfs exposure). To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2155617/+subscriptions