[Bug 220999] New: ASUS ExpertBook B1402CVA: Keyboard backlight brightness range incorrect (max=3, dim light)

[Bug 220999] New: ASUS ExpertBook B1402CVA: Keyboard backlight brightness range incorrect (max=3, dim light)

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=220999

            Bug ID: 220999
           Summary: ASUS ExpertBook B1402CVA: Keyboard backlight
                    brightness range incorrect (max=3, dim light)
           Product: Drivers
           Version: 2.5
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: low
          Priority: P3
         Component: Platform_x86
          Assignee: drivers_platform_x86@kernel-bugs.osdl.org
          Reporter: stefano.pascale04@gmail.com
        Regression: No

Created attachment 309219
  --> https://bugzilla.kernel.org/attachment.cgi?id=309219&action=edit
output of `dmidecode`

Hardware: ASUS ExpertBook B1402CVA
Kernel Version: 6.18.5-200.fc43.x86_64 (Fedora Rawhide)
CPU: 12 × 13th Gen Intel® Core™ i5-1335U

Description:
The keyboard backlight on this laptop is not working correctly with the
asus-wmi driver.
The system detects a `max_brightness` of 3. When setting brightness to 3, the
keyboard lights up but only at a very dim level (barely visible). Setting it to
1 or 2 turns it off completely.

It appears the hardware expects a range of 0-255 (or similar high value), but
the driver is limiting it to 0-3, possibly due to a missing quirk for this
specific model ID in the WMI driver.

Here is the sysfs output confirming the issue:

$ grep . /sys/class/leds/asus::kbd_backlight/*
/sys/class/leds/asus::kbd_backlight/brightness:0
/sys/class/leds/asus::kbd_backlight/brightness_hw_changed:0
/sys/class/leds/asus::kbd_backlight/max_brightness:3
/sys/class/leds/asus::kbd_backlight/trigger:[none] usb-gadget usb-host
rc-feedback kbd-scrolllock kbd-numlock kbd-capslock ... (truncated)

Steps to reproduce:
1. Boot Fedora 43 (Kernel 6.18).
2. Check /sys/class/leds/asus::kbd_backlight/max_brightness (Output is 3).
3. Set brightness to 3 (echo 3 | sudo tee ...). Result: Very dim light.

Troubleshooting attempted:
1. Tried boot param `acpi_osi=` and `acpi_osi="Windows 2020"` -> No change.
2. Tried `acpi_backlight=native` -> No interface created.
3. Tried `asusctl` -> Failed to set higher values.
4. Manually echoing values > 3 into 'brightness' -> No change.

Attached is the output of `dmidecode`.

I suspect this model needs a quirk in `drivers/platform/x86/asus-wmi.c` to
enable the correct brightness range.

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