[Bug 221800] New: HP ProBook 445 G9: keyboard backlight hotkey no longer works after upgrade to Linux 7.1.4

[Bug 221800] New: HP ProBook 445 G9: keyboard backlight hotkey no longer works after upgrade to Linux 7.1.4

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=221800

            Bug ID: 221800
           Summary: HP ProBook 445 G9: keyboard backlight hotkey no longer
                    works after upgrade to Linux 7.1.4
           Product: Drivers
           Version: 2.5
          Hardware: AMD
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: Platform_x86
          Assignee: drivers_platform_x86@kernel-bugs.osdl.org
          Reporter: bread708kms@gmail.com
        Regression: No

Created attachment 310526
  --> https://bugzilla.kernel.org/attachment.cgi?id=310526&action=edit
Diagnostic logs from the working kernel (Linux 7.1.3-arch1-2), including dmesg,
kernel journal, input device information, hardware information, evtest output,
and system configuration for comparison w

Overview

After upgrading from Linux 7.1.3-arch1-2 to Linux 7.1.4-arch1-1, the keyboard
backlight hotkey on my HP ProBook 445 G9 stopped working.

This is a regression, as downgrading only the Linux kernel back to
7.1.3-arch1-2 immediately restores the functionality.

No BIOS changes or userspace changes were made between the working and broken
tests.

Steps to Reproduce
Boot Linux 7.1.4-arch1-1 on an HP ProBook 445 G9.
Log into the system.
Press the keyboard backlight hotkey.
Optionally monitor /dev/input/event4 using evtest while pressing the key.
Actual Results

The keyboard backlight does not toggle.

evtest reports only the following when the key is pressed:

Event: type 4 (EV_MSC), code 4 (MSC_SCAN), value 43

No corresponding EV_KEY event is generated.

Other function keys (brightness, volume, etc.) continue to function normally.

The keyboard backlight hardware itself is functional, as it turns on after a
cold boot.

Expected Results

Pressing the keyboard backlight hotkey should generate the appropriate key
event and toggle the keyboard backlight, as it does on Linux 7.1.3-arch1-2.

Regression Information

Working kernel

Linux 7.1.3-arch1-2

Broken kernel

Linux 7.1.4-arch1-1

The issue is completely reproducible.

Downgrading only the kernel from 7.1.4 to 7.1.3 restores the keyboard backlight
hotkey functionality immediately.

Hardware

Laptop:

HP ProBook 445 G9

BIOS Version:

U88 Ver. 01.22.01

BIOS Date:

2026-05-04

Distribution:

Arch Linux
Additional Information

The hp_wmi driver is loaded.

dmesg contains:

hp_wmi: query 0x4 returned error 0x5

The system does not expose a keyboard backlight LED interface under
/sys/class/leds.

/proc/bus/input/devices identifies the internal keyboard as AT Translated Set 2
keyboard and the HP WMI device as HP WMI hotkeys.

If additional logs or testing are required, I would be happy to provide them.

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

[Bug 221800] HP ProBook 445 G9: keyboard backlight hotkey no longer works after upgrade to Linux 7.1.4

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=221800

bread708kms@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Regression|No                          |Yes

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

[Bug 221800] HP ProBook 445 G9: keyboard backlight hotkey no longer works after upgrade to Linux 7.1.4

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=221800

The Linux kernel's regression tracker (Thorsten Leemhuis) (regressions@leemhuis.info) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |regressions@leemhuis.info

--- Comment #1 from The Linux kernel's regression tracker (Thorsten Leemhuis) (regressions@leemhuis.info) ---
Thx for the report. Be aware that this report might reach the right people
here, but it might not, as the root of the problem is vague (could be input,
platform, or graphics drivers -- and even something else). To find the root of
the problem three things would be good:

* please attach dmesg from 7.1.3 and 7.1.4 directly (not in an archive, this is
to much or a hassle for some and bears risks, too)
* Does the same problem happen with 7.2-rc5
* Would be great if you could git bisect to find the change that broke things:
https://docs.kernel.org/admin-guide/bug-bisect.html

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.