Public bug reported:

ystem:

        Ubuntu 26.04.1
        Lenovo ThinkPad T14 Gen 5 Intel
        Affected kernel: 7.0.0-38-generic
        Working kernel: 7.0.0-34-generic

Description:

After upgrading the kernel from 7.0.0-34-generic to 7.0.0-38-generic,
screen brightness control stopped working. The display remains at
maximum brightness.

Both the keyboard brightness hotkeys and the GNOME Settings brightness
slider have no effect.

Steps to reproduce:

        Boot Ubuntu 26.04.1 with kernel 7.0.0-38-generic.
        Try to change screen brightness using the keyboard hotkeys.
        Observe that the display brightness remains at maximum.
        Reboot using kernel 7.0.0-34-generic.
        Verify that brightness control works again.

Expected result: Screen brightness can be adjusted using the keyboard
hotkeys.

Actual result: Brightness is stuck at maximum with kernel
7.0.0-38-generic.

This appears to be a kernel regression. The issue is reproducible on
this hardware and disappears when booting the previous kernel.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/2170625

Title:
  [REGRESSION] Screen brightness stuck at 100% on Lenovo ThinkPad T14
  Gen 5 Intel with kernel 7.0.0-38-generic

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