Ubuntu – Lenovo Y500 can’t set brightness

I've installed Ubuntu 12.10 on a Lenovo Y500 laptop (2012), video card is Nvidia 650M (no integrated graphics), I'm using driver 310.19. The problem is that I can't adjust brightness at all. If I press the relevant media keys, the indicator in ubuntu works correctly but the brightness is not changed.

So far I've tried the following:

Editing xorg.conf in this way:

Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    Option         "RegistryDwords" "EnableBrightnessControl=1"
EndSection

Adding the options acpi_osi=linux acpi_backlight=vendor to the grub boot options

Setting brightness from the terminal and using xbacklight. The values of /sys/class/backlight/acpi_video0/brightness can be changed as well but the brightness remains the same.

Do you have any other hints?

Solution

It is possible to enable the backlight by installing the nvidiabl module. First of all install git and dkms:

$ sudo apt-get install git dkms

Download the code on your machine and compile the package:

$ git clone https://github.com/guillaumezin/nvidiabl.git
$ cd nvidiabl
$ sudo make dkms-install

Now the module should be installed. To activate the nvidiabl module you should issue the command:

$ sudo modprobe nvidiabl

Now the directory /sys/class/backlight/nvidia_backlight/ should be present. In order to manually change the brightness you have to write in the brightness file:

$ sudo su
# echo 100 > /sys/class/backlight/nvidia_backligh/brightness

You can substitute 100 with any value up to 127. In my case not the complete range of backlight are supported. You can tune the brightness calibration by varying the min and max parameters (you will still have to write values in brightness up to 127):

$ sudo modprobe -r nvidiabl
$ sudo modprobe nvidiabl max=100000 min=10

You can load the module at startup by adding nvidiabl (with or without max and min parameters) to the file /etc/modules, but I still haven't figured out how to properly add hotkeys.