[Bug 2161780] Re: i915: eDP backlight dead after resume from suspend on Skylake (7.0.0-28 regression)

Status changed to 'Confirmed' because the bug affects multiple users. ** Changed in: linux (Ubuntu) Status: New => Confirmed -- You received this bug notification because you are subscribed to linux in Ubuntu. Matching subscriptions: Bgg, Bmail, Nb https://bugs.launchpad.net/bugs/2161780 Title: i915: eDP backlight dead after resume from suspend on Skylake (7.0.0-28 regression) Status in linux package in Ubuntu: Confirmed Bug description: On a Lenovo ThinkPad X1 Carbon (Skylake ULT, device ID 1916) running Ubuntu 26.04, the internal eDP panel loses its backlight after every resume from suspend. The panel still displays an image, but with no illumination, so it appears black. An external monitor attached via a USB-C dock is unaffected. The problem persists until reboot. While the backlight is dead, /sys/class/backlight/intel_backlight/brightness reads 1023 of a max 1023, and writes to it are accepted but have no effect. Forcing a modeset with xrandr, and switching VTs, both fail to restore it. The kernel log shows a clean "PM: suspend entry (deep)" and "PM: suspend exit" pair with no i915 messages in between and no errors. Regression details: - 7.0.0-27-generic: not affected - 7.0.0-28-generic: affected on every resume Workaround: booting 7.0.0-28-generic with i915.enable_dpcd_backlight=0 avoids the problem entirely. Given the workaround, I suspect the VESA/DPCD backlight series included in 7.0.0-28, in particular "drm/i915/backlight: Remove try_vesa_interface", "drm/i915/backlight: Check if VESA backlight is possible" and "drm/i915/backlight: Fix VESA backlight possible check condition". The panel may now be misdetected as supporting AUX/VESA backlight control, leaving the native PWM unarmed after resume. ProblemType: Bug DistroRelease: Ubuntu 26.04 Package: linux-image-7.0.0-28-generic 7.0.0-28.28 ProcVersionSignature: Ubuntu 7.0.0-28.28-generic 7.0.12 Uname: Linux 7.0.0-28-generic x86_64 NonfreeKernelModules: zfs ApportVersion: 2.34.1-0ubuntu0.1 Architecture: amd64 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/controlC0: mike 3719 F.... wireplumber /dev/snd/controlC1: mike 3719 F.... wireplumber /dev/snd/seq: mike 3713 F.... pipewire CasperMD5CheckResult: pass CurrentDesktop: ubuntu:GNOME Date: Sat Jul 25 14:46:46 2026 InstallationDate: Installed on 2025-09-20 (308 days ago) InstallationMedia: Ubuntu 25.04 "Plucky Puffin" - Release amd64 (20250415.3) MachineType: LENOVO 20K3A03DAU ProcFB: 0 i915drmfb ProcKernelCmdLine: BOOT_IMAGE=/BOOT/ubuntu_a5p21w@/vmlinuz-7.0.0-28-generic root=ZFS=rpool/ROOT/ubuntu_a5p21w ro quiet splash crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M i915.enable_dpcd_backlight=0 SourcePackage: linux UpgradeStatus: Upgraded to resolute on 2026-04-19 (97 days ago) dmi.bios.date: 02/15/2024 dmi.bios.release: 1.62 dmi.bios.vendor: LENOVO dmi.bios.version: N1MET77W (1.62 ) dmi.board.asset.tag: Not Available dmi.board.name: 20K3A03DAU dmi.board.vendor: LENOVO dmi.board.version: Not Defined dmi.chassis.asset.tag: DPC-PF0U3K8G dmi.chassis.type: 10 dmi.chassis.vendor: LENOVO dmi.chassis.version: None dmi.ec.firmware.release: 1.22 dmi.modalias: dmi:bvnLENOVO:bvrN1MET77W(1.62):bd02/15/2024:br1.62:efr1.22:svnLENOVO:pn20K3A03DAU:pvrThinkPadX1C5thW10DG:rvnLENOVO:rn20K3A03DAU:rvrNotDefined:cvnLENOVO:ct10:cvrNone:skuLENOVO_MT_20K3_BU_Think_FM_ThinkPadX1C5thW10DG:pfaThinkPadX1C5thW10DG: dmi.product.family: ThinkPad X1C 5th W10DG dmi.product.name: 20K3A03DAU dmi.product.sku: LENOVO_MT_20K3_BU_Think_FM_ThinkPad X1C 5th W10DG dmi.product.version: ThinkPad X1C 5th W10DG dmi.sys.vendor: LENOVO To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2161780/+subscriptions