[Bug 2162631] Re: Intel backlight regression on Lenovo ThinkPad T450s after upgrading from Linux 7.0.0-27 to 7.0.0-28

i had to move back to 7.0.0-27 so i can use the pc well -- You received this bug notification because you are subscribed to linux in Ubuntu. Matching subscriptions: Bgg, Bmail, Nb https://bugs.launchpad.net/bugs/2162631 Title: Intel backlight regression on Lenovo ThinkPad T450s after upgrading from Linux 7.0.0-27 to 7.0.0-28 Status in linux package in Ubuntu: New Bug description: Brightness control works correctly with Linux kernel `7.0.0-27-generic` but stops working after booting into `7.0.0-28-generic`. The brightness slider and sysfs values change normally, but the physical display brightness does not change. This appears to be an Intel i915 graphics driver regression introduced in kernel `7.0.0-28`. ## Hardware Laptop: * Lenovo ThinkPad T450s Graphics: * Intel integrated graphics * Intel Broadwell/ULT GPU * PCI device ID: 1616 Display: * Internal eDP panel ## Operating System Ubuntu 26.04 LTS (Resolute) Desktop session: * GNOME * Wayland ## Affected kernels ### Working kernel ``` Linux 7.0.0-27-generic ``` Brightness works normally. Kernel command line: ``` BOOT_IMAGE=/boot/vmlinuz-7.0.0-27-generic root=UUID=06789976-622b-4eb6-9e48-b0a08facff37 ro quiet splash i915.enable_psr=0 crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M ``` ### Broken kernel ``` Linux 7.0.0-28-generic ``` Brightness control does not affect the physical display. Kernel command line: ``` BOOT_IMAGE=/boot/vmlinuz-7.0.0-28-generic root=UUID=06789976-622b-4eb6-9e48-b0a08facff37 ro quiet splash i915.enable_psr=0 crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M ``` ## Reproduction steps 1. Boot into kernel: ``` 7.0.0-28-generic ``` 2. Change brightness using GNOME brightness controls or: ``` brightnessctl set 50% ``` 3. The brightness value changes, but the display brightness remains unchanged. 4. Boot into: ``` 7.0.0-27-generic ``` 5. Repeat the same test. Result: * Brightness works correctly on 7.0.0-27. ## Backlight interface The system exposes: ``` /sys/class/backlight/intel_backlight ``` Output: ``` lrwxrwxrwx intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card1/card1-eDP-1/intel_backlight ``` Maximum brightness: ``` 1023 ``` On kernel 7.0.0-28: ``` brightness: 627 actual_brightness: 627 ``` Changing values works: ``` echo 100 | sudo tee /sys/class/backlight/intel_backlight/brightness 100 echo 800 | sudo tee /sys/class/backlight/intel_backlight/brightness 800 ``` However, the physical screen brightness does not change. ## i915 driver information Working kernel: ``` modinfo i915 srcversion: 042D149A3C0CF120B518B19 vermagic: 7.0.0-27-generic SMP preempt mod_unload modversions ``` Broken kernel: ``` modinfo i915 srcversion: 7F187B928024528F00EC733 vermagic: 7.0.0-28-generic SMP preempt mod_unload modversions ``` ## i915 logs from broken kernel ``` i915 0000:00:02.0: [drm] Found broadwell/ult (device ID 1616) integrated display version 8.00 stepping N/A i915 0000:00:02.0: [drm] Initialized i915 1.6.0 for 0000:00:02.0 on minor 1 i915drmfb (fb0) is primary device ``` No obvious i915 errors appear. ## Additional testing The following kernel parameter was already enabled: ``` i915.enable_psr=0 ``` The issue remains. The following was tested: ``` echo 100 | sudo tee /sys/class/backlight/intel_backlight/brightness echo 800 | sudo tee /sys/class/backlight/intel_backlight/brightness ``` The sysfs values change, but hardware brightness does not. ## Expected behavior Changing brightness should physically change the display brightness. ## Actual behavior Brightness values update in sysfs and GNOME UI, but the display brightness remains unchanged. ## Regression range Last working: ``` 7.0.0-27-generic ``` First broken: ``` 7.0.0-28-generic ``` ## Possible cause This looks like a regression in the Intel i915 backlight handling introduced between kernel versions 7.0.0-27 and 7.0.0-28. ProblemType: Bug DistroRelease: Ubuntu 26.04 Package: linux-image-7.0.0-27-generic 7.0.0-27.27 ProcVersionSignature: Ubuntu 7.0.0-27.27-generic 7.0.6 Uname: Linux 7.0.0-27-generic x86_64 ApportVersion: 2.34.1-0ubuntu0.1 Architecture: amd64 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/controlC1: jotech 4200 F.... wireplumber /dev/snd/controlC0: jotech 4200 F.... wireplumber /dev/snd/seq: jotech 4191 F.... pipewire CasperMD5CheckResult: pass CurrentDesktop: ubuntu:GNOME Date: Sat Aug 1 15:46:19 2026 InstallationDate: Installed on 2026-05-12 (81 days ago) InstallationMedia: Ubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423.1) MachineType: LENOVO 20BWS4BP00 ProcEnviron: LANG=en_US.UTF-8 PATH=(custom, no user) SHELL=/bin/bash TERM=xterm-256color XDG_RUNTIME_DIR=<set> ProcFB: 0 i915drmfb ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-7.0.0-27-generic root=UUID=06789976-622b-4eb6-9e48-b0a08facff37 ro quiet splash i915.enable_psr=0 crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M SourcePackage: linux UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 08/14/2019 dmi.bios.release: 1.37 dmi.bios.vendor: LENOVO dmi.bios.version: JBET73WW (1.37 ) dmi.board.asset.tag: Not Available dmi.board.name: 20BWS4BP00 dmi.board.vendor: LENOVO dmi.board.version: SDK0J40705 WIN dmi.chassis.asset.tag: No Asset Information dmi.chassis.type: 10 dmi.chassis.vendor: LENOVO dmi.chassis.version: None dmi.ec.firmware.release: 1.4 dmi.modalias: dmi:bvnLENOVO:bvrJBET73WW(1.37):bd08/14/2019:br1.37:efr1.4:svnLENOVO:pn20BWS4BP00:pvrThinkPadT450s:rvnLENOVO:rn20BWS4BP00:rvrSDK0J40705WIN:cvnLENOVO:ct10:cvrNone:skuLENOVO_MT_20BW_BU_Think_FM_ThinkPadT450s:pfaThinkPadT450s: dmi.product.family: ThinkPad T450s dmi.product.name: 20BWS4BP00 dmi.product.sku: LENOVO_MT_20BW_BU_Think_FM_ThinkPad T450s dmi.product.version: ThinkPad T450s dmi.sys.vendor: LENOVO To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2162631/+subscriptions