Created attachment 74171 [details]
On an Ubuntu 12.04 PC with Linux 3.2.0-26-generic x86_64 and
AMD (ATI) Radeon HD 4350 VGA controller the kernel does not recognize
the ability of the VGA to change brightness of the connected monitor
/sys/class/backlight/ is empty and tools for brightness control report
errors. I tried the following options in /etc/default/grub (and
updated grub configuration after the change):
GRUB_CMDLINE_LINUX="pcie_aspm=force acpi_osi=Linux acpi_backlight=vendor"
but to no avail.
Created attachment 74181 [details]
output of lsmod
Created attachment 74191 [details]
output of 'sudo lspci -vvnn'
Created attachment 74201 [details]
output of 'sudo acpidump'
there is no ACPI Backlight control on your laptop.
so sorry I can not help you on this.
re-assign to the graphics expert.
If your laptop uses the backlight controller on the GPU, there is support for it in kernel 3.7.