Ubuntu
linux package

  1. Bug #518002
  2. Comment #32

Comment 32 for bug 518002

Revision history for this message
Wolfgang Kufner (wolfgangkufner) wrote : Re: lucid extensa 5635z backlight dimming not working at all

I looked some more into this setpci workaround to see where that magical F4 address comes from:
sudo setpci -s 00:02.0 F4.B=a1 writes the brightness value (a1 in this example) directly into a register called "Legacy Backlight Brightness" (at address F4) of the [8086:2a42] hardware.
The fact that there is such a register at that address can be found in the manufacturers documentation http://www.intel.com/Assets/PDF/datasheet/320122.pdf for that ([8086:2a42]) hardware.
(btw. my other notebook with same graphics id where backlight setting works out of the box does ignore values written into the F4 register)

@maxwel cecato mavigno,
I assume that lspci -nn|grep VGA gives you [8086:0044] as identification for your hardware.
I looked into
http://download.intel.com/design/processor/datashts/322812.pdf
http://download.intel.com/design/processor/datashts/322813.pdf
which is the datasheet intel published for the mobile i3 ([8086:0044]).
I could not find a "Legacy Backlight Brightness" register there, so that workaround should not work here.
In short, you have a different hardware, so I recommend that you file a new bug report with "ubuntu-bug linux".