Ubuntu Wiki

• Launchpad Entry:

• Created: 2007-05-17

• Contributors: Erik Andrén - erik.andren / A T \ gmail.com

• Packages affected: Hal, libsmbios

Summary

Backlight support on Dell machines is now possible, only some coordination is missing.

Rationale

HAL (Hardware Abstraction Layer) >= 0.5.9 contains support for backlight on Dell laptops, this is unfortunately disabled in the Ubuntu HAL package. The missing piece is that Ubuntu needs to ship the libsmbios library (currently available in Universe) and the kernel module dcdbas needs to be manually loaded. Implementing this feature is especially important as Dell starts to ship Ubuntu laptops.

Use Cases

• George has bought a Dell laptop and wants to alter the brightness level of his screen to conserve battery power. He uses the brightness applet in the panel to decrease it.

Scope

This feature shall be enabled by default on normal desktop builds, working out of the box.

Design and Implementation

• libsmbios needs to be shipped by default on at least desktop systems and have a version greater or equal to 0.13.4
• HAL needs to be rebuilt on a machine with libsmbios installed, enabling Dell backlight support.
• The dcdbas module needs to be manually loaded. Some discussion has been done in the udev mailing list trying to resolve this issue, making it possible to autodetect when this module is needed. Unfortunately, no real ideas exist at the moment. The easy solution is to add dcdbas to the /etc/modules list

Unresolved issues

Autoprobing of the dcdbas module would be favorable.

More Information

https://bugs.launchpad.net/ubuntu/+source/hal/+bug/43572 - Tracks this issue