[Bug 214899] New: ideapad-laptop: platform backlight device not working

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=214899

            Bug ID: 214899
           Summary: ideapad-laptop: platform backlight device not working
           Product: Drivers
           Version: 2.5
    Kernel Version: 5.10.27-5.14.15
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Platform_x86
          Assignee: drivers_platform_x86@kernel-bugs.osdl.org
          Reporter: johannes.penssel@gmail.com
        Regression: No

Created attachment 299379
  --> https://bugzilla.kernel.org/attachment.cgi?id=299379&action=edit
DSDT.dsl

Hardware: Lenovo IdeaPad 5 15ITL05, latest BIOS version
Issue: Platform backlight device provided by ideapad-laptop has no effect on
actual brightness.
Pressing brightness keys on my keyboard causes changes in
/sys/class/backlight/ideapad/actual_brightness, but no uevent is generated (as
outlined in drivers/video/backlight.c source code comments), and
/sys/class/backlight/ideapad/brightness is unaffected. 
When manipulating /sys/class/backlight/ideapad/brightness directly, uevents are
being generated, but no change in real screen brightness occurs. 
The only way that screen brightness can actually be changed is by using i915's
intel_backlight sysfs interface, which does not respond to brightness keyboard
keys.

attached is my decompiled DSDT and dmesg.

ls -la /sys/class/backlight/ideapad/
total 0
drwxr-xr-x 3 root root     0 Oct 31 19:40 .
drwxr-xr-x 3 root root     0 Oct 31 19:40 ..
-r--r--r-- 1 root root  4096 Oct 31 19:40 actual_brightness
-rw-r--r-- 1 root root  4096 Oct 31 19:40 bl_power
-rw-rw-r-- 1 root video 4096 Oct 31 19:43 brightness
lrwxrwxrwx 1 root root     0 Oct 31 19:40 device -> ../../../VPC2004:00
-r--r--r-- 1 root root  4096 Oct 31 19:40 max_brightness
drwxr-xr-x 2 root root     0 Oct 31 19:40 power
-r--r--r-- 1 root root  4096 Oct 31 19:40 scale
lrwxrwxrwx 1 root root     0 Oct 31 19:40 subsystem ->
../../../../../../../class/backlight
-r--r--r-- 1 root root  4096 Oct 31 19:40 type
-rw-r--r-- 1 root root  4096 Oct 31 19:40 uevent

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