Screen Brightness Bug - Ubuntu 12.04

The screen brightness always start with 100% and typing the Fn + F2/F3 keys only makes to appear the pointer on the screen, but doesn't work.

To change the screen brightness, only in the System Configurations – Brightness and Block, “every time that one switch on or restart the notebook”.

If one want to change again “ in the same session”, when the application window opens the screen brightness return to 100%.

I solve this problem changing the command line:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

to

GRUB_CMDLINE_LINUX_DEFAULT="quiet acpi_osi=Linux acpi_backlight=vendor splash"

even thus, at every restart one need to change the brightness, the configuration doesn't hold.

My Notebook:
Samsung model 300E4A-AD1
Intel Core i5 2450M
Ubuntu 12.04 64bits
Graphic Processor Intel GMA HD
Chipset Intel HM65