samsung-laptop backlight control not working

[David Herrmann]

Hi

I tried the new samsung-laptop driver with samsung backlight support.
It is detected as:
[109282.931433] samsung_laptop: found laptop model 'N150P/N210P/N220P'

However, backlight support is kind of weird:
"echo 1 >/sys/class/backlight/samsung/brightness"
does not set brightness to 1 but instead reduces brightness for 1.
That is, if my current brightness setting is 8, I need to call "echo 1
>..." 7 times to get brightness value 1.

"cat /sys/class/backlight...."
returns 1 after the first try, though.

"echo 3 >..."
reduces brightness also for 1 but stops at brightness level 3 if I
repeat the command.

dmesg shows the following for every "echo" I call:
[110690.073783] ACPI: Failed to switch the brightness

Furthermore "echo 0 >..." doesn't disable backlight but instead
behaves like a brightness setting below 1.


However, I know the following works on my machine:
setpci -s 00:02.0 F4.B=255
It accepts a setting between 0-255 and 255 is full brightness and 0 is
backlight off.


Regards
David
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