Public bug reported:
Since linux 7.0.0-28.28 (resolute) the internal eDP panel of a ThinkPad
T480 no longer comes back after the first suspend/resume (S3, "deep").
The external HDMI monitor resumes normally. Only a reboot restores the
internal panel. 7.0.0-27 and earlier are fine.
Hardware
- ThinkPad T480 20L6S68T2W, BIOS N24ET81W (1.56), Intel Kaby Lake-R UHD
Graphics 620 [8086:5917] rev 07, i915
- Internal panel: LG Display LP140WF6-SPB7 (EDID LGD 0x1313), 1920x1080 eDP,
PWM backlight (intel_backlight)
- Ubuntu 26.04 LTS, KDE Plasma 6.6.6 / KWin 6.6.6 Wayland, Secure Boot on
(lockdown=integrity)
- mem_sleep: s2idle [deep] (S3), no custom kernel parameters before the
workaround
Symptom after resume (all observed on 7.0.0-30, identical on -28/-29)
- eDP-1: status=connected, enabled=enabled, dpms=On; KWin drives it at
1920x1080@60 (kscreen-doctor shows it enabled, brightness control "supported")
- /sys/class/backlight/intel_backlight: brightness writes are accepted and read
back (308 -> 1023 -> 308), bl_power=0
- Panel stays completely black with NO backlight glow even at brightness 1023;
also no faint image with a flashlight
- Toggling bl_power 1/0, kscreen-doctor output.eDP-1.disable/enable, and
kscreen-doctor --dpms off/on do NOT bring the backlight back
- Zero i915/drm errors in dmesg around suspend/resume
- eDP has no i915_psr_status entry in debugfs (PSR not used on this panel) so
PSR is not involved
Regression window (from journalctl --list-boots, counting "PM: suspend exit"
per boot)
- 7.0.0-22: 29 and 60 suspends per boot, fine (June 2026)
- 7.0.0-27: 13, 16, 5, 21 suspends per boot, fine (2 to 27 July 2026)
- 7.0.0-28 (installed 28 July): every boot since then has 0 or 1 suspend
followed by a reboot, because the panel never came back
- 7.0.0-29 and 7.0.0-30: same as -28
The 7.0.0-28 changelog contains the backported series "Internal display black
screen on Intel Lunar Lake with eDP panel" (LP: #2156312), including:
- drm/i915/backlight: Remove try_vesa_interface
- drm/i915/backlight: Take luminance_set into account for VESA backlight
- drm/i915/backlight: Check luminance_set when disabling PWM via AUX VESA
backlight
- drm/i915/backlight: Short circuit intel_dp_aux_supports_hdr_backlight
- drm/i915/backlight: Check if VESA backlight is possible
- drm/i915/backlight: Fix VESA backlight possible check condition
These change PWM vs DPCD/VESA AUX backlight selection, which matches the
symptom (image path fine, PWM backlight not re-enabled on resume).
Workaround (verified)
echo 'options i915 enable_dpcd_backlight=0' > /etc/modprobe.d/i915-resume.conf
update-initramfs -u -k all
With this option on 7.0.0-30 the internal panel comes back after
suspend/resume. /sys/module/i915/parameters/enable_dpcd_backlight reads 0.
Expected: the internal panel backlight is re-enabled on resume with the
default enable_dpcd_backlight=-1, as it was up to 7.0.0-27.
Happy to test a kernel with the series reverted or with a fix, or to
provide drm.debug logs of a resume.
Related to bug #2156312 (the backported series that introduced the
change)
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: linux-image-7.0.0-30-generic 7.0.0-30.30
ProcVersionSignature: Ubuntu 7.0.0-30.30-generic 7.0.12
Uname: Linux 7.0.0-30-generic x86_64
ApportVersion: 2.34.1-0ubuntu0.1
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: zak 2240 F.... wireplumber
/dev/snd/seq: zak 2211 F.... pipewire
CasperMD5CheckResult: unknown
CurrentDesktop: KDE
Date: Fri Sep 4 02:52:45 2026
InstallationDate: Installed on 2026-02-21 (194 days ago)
InstallationMedia: Kubuntu 25.10 "Questing Quokka" - Release amd64 (20251007)
MachineType: LENOVO 20L6S68T2W
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-7.0.0-30-generic
root=UUID=4d75fb6a-ab95-47a9-a69a-43be15458017 ro quiet
rd.luks.uuid=47b20a4b-446e-40c3-9513-2d48d619f414 splash
PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No
PulseAudio daemon running, or not running as session daemon.
SourcePackage: linux
UpgradeStatus: Upgraded to resolute on 2026-05-22 (104 days ago)
dmi.bios.date: 09/06/2025
dmi.bios.release: 1.56
dmi.bios.vendor: LENOVO
dmi.bios.version: N24ET81W (1.56 )
dmi.board.asset.tag: Not Available
dmi.board.name: 20L6S68T2W
dmi.board.vendor: LENOVO
dmi.board.version: SDK0J40697 WIN
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: None
dmi.ec.firmware.release: 1.22
dmi.modalias:
dmi:bvnLENOVO:bvrN24ET81W(1.56):bd09/06/2025:br1.56:efr1.22:svnLENOVO:pn20L6S68T2W:pvrThinkPadT480:rvnLENOVO:rn20L6S68T2W:rvrSDK0J40697WIN:cvnLENOVO:ct10:cvrNone:skuLENOVO_MT_20L6_BU_Think_FM_ThinkPadT480:pfaThinkPadT480:
dmi.product.family: ThinkPad T480
dmi.product.name: 20L6S68T2W
dmi.product.sku: LENOVO_MT_20L6_BU_Think_FM_ThinkPad T480
dmi.product.version: ThinkPad T480
dmi.sys.vendor: LENOVO
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug regression-update resolute wayland-session
--
You received this bug notification because you are a member of Ubuntu
Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/2166429
Title:
[regression 7.0.0-28] ThinkPad T480 (UHD 620): internal eDP backlight
stays off after suspend/resume, i915.enable_dpcd_backlight=0 fixes it
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2166429/+subscriptions
--
ubuntu-bugs mailing list
[email protected]
https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
