Additional regression information:

Hardware:
- Acer Aspire 7 A715-76G
- Intel Alder Lake-P UHD Graphics (8086:46a3)

Working kernel:
7.0.0-27-generic

Broken kernels:
7.0.0-28-generic
7.0.0-29-generic

Results:

Kernel 7.0.0-27:
$ cat /sys/class/backlight/intel_backlight/max_brightness
19200

Brightness keys, GNOME brightness slider and direct writes to:
/sys/class/backlight/intel_backlight/brightness
all change the physical panel brightness.

Kernel 7.0.0-29:
$ cat /sys/class/backlight/intel_backlight/max_brightness
32767

The sysfs brightness value changes, but the physical panel brightness
never changes.

The following were tested without success:
- acpi_backlight=native
- removing acpi_backlight=native
- writing directly to /sys/class/backlight/intel_backlight/brightness

This appears to be a regression introduced after kernel 7.0.0-27.

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https://bugs.launchpad.net/bugs/2162884

Title:
  Regression: Intel backlight no longer works on Acer Aspire 7 after
  upgrade from 7.0.0-27 to 7.0.0-29

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