Public bug reported:
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
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug resolute wayland-session
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https://bugs.launchpad.net/bugs/2161780
Title:
i915: eDP backlight dead after resume from suspend on Skylake
(7.0.0-28 regression)
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