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I can't change my screen brightness by pressing brightness keys on the keyboard, but they change through /sys/class/backlight/acpi_video0/brightness. So I started to diagnose the issue. I ran xev, and I'm trying to see what happens when I press Fn+F5 or Fn+F6, which are brightness controls, and xev didn't show anything. I must note that it notifies my when I press volume controls, for example.
are F5 and F6 keys working? yes, but not when I press them with Fn key.
do I have any entry in xmodmap for brightness? yes:
keycode 232 = XF86MonBrightnessDown NoSymbol XF86MonBrightnessDown
keycode 233 = XF86MonBrightnessUp NoSymbol XF86MonBrightnessUp

What's happening, and what should I do to correct it?
I'm using vaio S series laptop with kubuntu precise on it.

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Do you have xkeycaps installed? With that you could set the correct layout so that the Fn key is recognized. –  ott-- Sep 7 '12 at 17:20
    
the Fn key is recognized very well, i can use it to change volume, for example. the problem is with combination of Fn+F5 –  sazary Sep 7 '12 at 21:23
    
You don't happen to be talking about a Zenbook do you? Either way I think the answer might be that the acpi driver does not support those keys yet, either that or we're not using the right one. –  Jamie Kitson Sep 15 '12 at 22:13
    
I've reported a bug: dev.iksaif.net/issues/248 –  Jamie Kitson Sep 15 '12 at 23:07
    
no, i'm using a vaio vpcs136fg machine; so i think the place that you've reported the bug to is irrelevant. yet i appreciate your attention ;) –  sazary Sep 16 '12 at 18:06

1 Answer 1

You can start by researching the drivers which are used for your ACPI keys and finding instructions on how to configure your ACPI daemon. The chances are your laptop is supported in the kernel (linux), so making things work is a matter of loading the correct module (modprode sony_laptop).

from menuconfig in /use/src/linux:

 CONFIG_SONY_LAPTOP:                                                            
  │ This mini-driver drives the SNC and SPIC devices present in the ACPI      
  │ BIOS of the Sony Vaio laptops.                                            
  │ It gives access to some extra laptop functionalities like Bluetooth,      
  │ screen brightness control, Fn keys and allows powering on/off some        
  │ devices.                                                                  
  │ Read <file:Documentation/laptops/sony-laptop.txt> for more information.  

For example, on my EEE PC I have a module called eeepc_laptop (CONFIG_EEEPC_LAPTOP in /usr/src/linux/.config) which is responsible for handling the power-management features and the Fn-keys:

$ lsmod  | grep eee
eeepc_laptop           12682  0 
sparse_keymap           2733  1 eeepc_laptop

The acpi-events generated by the keys can be monitored (to verify that they are working) by running acpi_listen and pressing a few Fn-keys.

$ acpi_listen 
hotkey ATKD 0000002f 00000078
hotkey ATKD 0000002e 00000003

On my system, the acpi daemon detects such events with scripts in /etc/acpi/events/ and scripts in /etc/acpi/actions/ do certain things when the events are detected. I'm only saying this to give you a sense of orientation. Chances are your distribution ships with a well configured ACPI daemon (maybe not the same as mine). Again, check their Wiki or Handbook.

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