How do i make screen dimming work in ubuntu 12.04 (beta 2)

I recently installed Ubuntu 12.04 (beta 2) on my HP mini 110-4117, but I cant control screen brightness. The Fn + F2 , Fn + F3 keys don't work. System Settings > Brightness and Lock doesn't provide any means of controlling screen brightness.

How can this be fixed? Thank you.

Here is what worked for me. I got the solution from the folowing links. Check them out or read the summary below.

http://linuxon1001p.blogspot.com/2010/03/fixing-brightness-controls.html

Desktop doesn't remember brightness settings after a reboot

Summary:

1. Edit your /etc/default/grub file:

   sudo gedit /etc/default/grub

2. Add the options "acpi_osi=Linux acpi_backlight=vendor" to the GRUB_CMDLINE_LINUX_DEFAULT line. It should look like this:

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

   original line was:

   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

3. Update grub configuration!!!! - do not forget to do this, the configuration change will not be set up if you don't run the next command:

   sudo update-grub

This worked for me after trying a lot of other solutions. I have a HP dv7-6090ef with hybrid graphics Intel/AMD.

Have fun using Ubuntu!