Public bug reported:
[Impact]
The internal display backlight is unusable after upgrading from linux-
image-7.0.0-27-generic to linux-image-7.0.0-28-generic on a Dell
Latitude 5320 laptop.
The issue affects the internal panel only. External monitors continue to
work.
[Steps to reproduce]
1. Boot Ubuntu 26.04 with kernel 7.0.0-28-generic.
2. Do not add any kernel parameter.
3. After i915 loads, the internal display backlight turns almost completely off.
4. The image is still visible with a flashlight, but the backlight is
effectively disabled.
5. Brightness controls appear to work, but have no visible effect.
[Expected behaviour]
The internal display backlight should work normally, as it does with
kernel 7.0.0-27-generic.
[Regression]
Working:
- linux-image-7.0.0-27-generic
Broken:
- linux-image-7.0.0-28-generic
[Workaround]
Adding the kernel parameter:
i915.enable_dpcd_backlight=0
restores normal backlight operation on kernel 7.0.0-28.
[Hardware]
Dell Latitude 5320
Intel Tiger Lake integrated graphics
PCI device: Intel Corporation TigerLake-LP GT2 [Iris Xe Graphics] (device ID
9a49)
[Additional information]
Without the workaround, brightnessctl reports:
Device 'intel_backlight' of class 'backlight':
Current brightness: 1023 (100%)
Max brightness: 1023
However, the physical backlight is effectively off.
The issue started immediately after the kernel update to 7.0.0-28.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2161244
Title:
Regression in linux 7.0.0-28: Intel Tiger Lake internal display
backlight disabled unless i915.enable_dpcd_backlight=0
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