Display brightness on kernel 6.2+

English Hardware
#1

Dell Precision M4800 laptop

Controls for display brightness function properly through kernel 6.1.x

Beginning with kernel 6.2.0 up thru 6.3rc3 no action changes display brightness: keyboard Fn keys, scroll on Battery & Brightness icon, slider in Battery & Brightness control. The keyboard brightness control does function properly with both keyboard Fn keys and slider in Battery & Brightness control.

Is this a kernel regression? a powerdevil regression? Who would be responsible to fix it?

#2

Maybe this note in the ArchWiki Backlight article: <https://wiki.archlinux.org/title/Backlight>

Since Linux 6.1 the backlight subsystem was revamped, if your backlight does not work after an update first try to remove an existing acpi_backlight kernel parameter.

#3

There is no “acpi_backlight=video” parameter on the kernel commandline. Adding it does not change anything.

What I have determined is that kernel 6.1.x shows only “nv_backlight” as the result of “ls /sys/class/backlight” while the same command in kernel 6.2.x shows only “acpi_video0”. The refactoring for 6.1 didn’t break anything for me, it only happened with 6.2. I sent Hans the 4 text files, maybe they will be helpful for him.

#4

What is the output of the following command (6.1.x and then 6.2.x)?

 > cat /sys/class/backlight/nv_backlight
 > cat /sys/class/backlight/acpi_video0
#5

6.1.x

cat /sys/class/backlight/nv_backlight: Is a directory
cat /sys/class/backlight/acpi_video0: No such file or directory

6.2.x

cat /sys/class/backlight/nv_backlight: No such file or directory
cat /sys/class/backlight/acpi_video0: Is a directory