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

Public bug reported: 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). ** Affects: linux (Ubuntu) Importance: Undecided Status: New -- 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