Public bug reported:
SUMMARY
After resume from suspend (S3), the internal laptop panel (eDP-1) stays
completely dark on kernel 7.0.0-28-generic. The panel is still rendering
(content is visible when illuminating the panel from the side with an
external light source) — only the backlight is not re-enabled.
Booting kernel 6.17.0-40-generic on the exact same system resolves the
issue completely: suspend/resume works and the backlight comes back on.
This is therefore a regression introduced between 6.17 and 7.0.
HARDWARE
Lenovo ThinkPad T480, machine type 20L5000BGE
CPU: Intel Core i7-8550U (Kaby Lake Refresh)
GPU: Intel UHD 620 (i915) + NVIDIA MX150 (hybrid, PRIME on-demand)
BIOS: N24ET81W (1.56), also reproduced with 1.50
Display: internal eDP-1 (2560x1440), external monitor via HDMI-2
SOFTWARE
Linux Mint 22.3 Cinnamon (Ubuntu 24.04 noble base)
X11 session (XDG_SESSION_TYPE=x11)
Affected kernel: 7.0.0-28-generic
Working kernel: 6.17.0-40-generic
STEPS TO REPRODUCE
1. Boot kernel 7.0.0-28-generic
2. Suspend the system (S3)
3. Resume the system
4. Internal panel eDP-1 stays dark; system is fully functional otherwise
EXPECTED: backlight is re-enabled on resume
ACTUAL: backlight stays off; panel still renders content
KEY OBSERVATION
All software layers report a correct state while the panel is physically dark:
/sys/class/backlight/intel_backlight/brightness = 900
/sys/class/backlight/intel_backlight/max_brightness = 1023
/sys/class/backlight/intel_backlight/actual_brightness = 900
/sys/class/backlight/intel_backlight/bl_power = 0
So the driver believes the backlight is enabled at ~88%, and the hardware
reports back the same value, but no light is emitted. There are no i915
error messages in the kernel log during resume.
RESUME LOG (kernel 7.0.0-28, no i915 errors):
kernel: PM: suspend entry (deep)
kernel: ACPI: PM: Preparing to enter system sleep state S3
kernel: ACPI: PM: Low-level resume complete
kernel: ACPI: PM: Waking up from system sleep state S3
kernel: nvidia 0000:01:00.0: Enabling HDA controller
kernel: xhci_hcd 0000:3c:00.0: xHC error in resume, USBSTS 0x401, Reinit
kernel: PM: suspend exit
(the xhci error is USB-related and unrelated to the display)
THINGS RULED OUT BY TESTING
- Writing brightness via sysfs (same value and different value): no effect
- DPMS off/on (xset dpms force off/on): no effect
- VT switch to text console: no effect
- Forced modeset on eDP-1 only (xrandr --output eDP-1 --off / --auto):
works fine while the panel is lit, but as a systemd-sleep post hook it
made things worse (panel then stayed dark permanently)
- Disabling nvidia-suspend/nvidia-resume/nvidia-hibernate services: no effect
- Second suspend/resume cycle: panel stays dark (does not self-recover)
- External monitor: issue also occurs with no external monitor attached
- BIOS update 1.50 -> 1.56: no effect
- Kernel parameter acpi_backlight=video: no effect
- Cold boot always works: the panel is lit normally after a full reboot,
the issue is strictly resume-specific
ADDITIONAL NOTE
Only intel_backlight is exposed in /sys/class/backlight; no acpi_video0
interface is created, although thinkpad_acpi reports:
"This ThinkPad has standard ACPI backlight brightness control, supported
by the ACPI video driver"
Note: this system runs Linux Mint 22.3 (Ubuntu 24.04 base), so the report
was filed manually instead of via ubuntu-bug/apport, which is not
installed by default on Mint.
Please let me know if you need any further logs or tests — I can boot
either kernel on demand and reproduce reliably.
VERSION SIGNATURE (working kernel, currently booted)
Ubuntu 6.17.0-40.40~24.04.1-generic 6.17.13
Note: the version signature of the affected kernel (7.0.0-28-generic)
could not be captured in the same session, since the machine currently
boots the working 6.17 kernel by default. It is still installed and I
can boot it and provide the signature on request.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: backlight i915 kabylake noble regression-release suspend-resume
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https://bugs.launchpad.net/bugs/2161599
Title:
[regression] i915: internal eDP-1 backlight stays off after resume on
kernel 7.0, works on 6.17 (ThinkPad T480, Kaby Lake R)
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