Comment 4 for bug 1104529

FWIW

Mine is a different Samsung machine (NP900x3d), my Ubuntu version is 12.10. I've tried with/without acpi_backlight=vendor .

More precisely this is my current boot command line:

luis@sams9:~$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-3.5.0-26-generic root=... ro quiet splash i915.i915_enable_rc6=1 i915.i915_enable_fbc=1 i915.lvds_downclock=1 vt.handoff=7

(The i915* options are my own customizations)

The output:

* with acpi_backlight=vendor added (Fn key combination does not work):

[ 5.613] (--) intel(0): found backlight control interface /sys/class/backlight/samsung

* without acpi_backlight=vendor, as it is in the referred /proc/cmdline (Fn key combination works):

[ 5.097] (--) intel(0): found backlight control interface /sys/class/backlight/acpi_video0

The weird thing is that acpi_backlight=verdor worked when BIOS was in UEFI mode. I've changed this to CSM mode after some research about the infamous firmware bug:

http://mjg59.dreamwidth.org/22855.html

Unfortunately I cannot provide more info for the UEFI mode.

The main advantage of using the samsung interface is that the minimum brightness threshold is lesser than in the native acpi_video interface, the former allows to dim completely the screen with the corresponding gaining in power saving.