Re: 8086:2a42 [Asus UL80VT] Backlight control does not work with Intel integrated card, but there are entries in /sys/class/backlight

[Guillaume Millet <gmillet@crans.org>]

Le 03/12/2013 05:25, Aaron Lu a écrit :
> On 12/03/2013 12:53 AM, Guillaume Millet wrote:
>> Hello, I report an issue, in attempting to follow the instructions at
>> https://wiki.ubuntu.com/Bugs/Upstream/kernel#KernelTeam.2BAC8-KernelTeamBugPolicies.Overview_on_Reporting_Bugs_Upstream
>>
>> [1.] 8086:2a42 [Asus UL80VT] Backlight control does not work with Intel
>> integrated card, but there are entries in /sys/class/backlight
>>
>> [2.] The screen brightness control has apparently never worked
>> off-the-shelf on this laptop, Asus UL80VT-A1, which is an NVIDIA Optimus
>> laptop (2 graphic cards). The use of the discrete Nvidia card is managed
>> by Bumblebee (https://wiki.ubuntu.com/Bumblebee). It used to work with
>> the workaround suggested at
>> http://wiki.daviddarts.com/Ubuntu_Maverick_on_the_Asus_UL30VT#Screen_Brightness  
>> which modifies asus-brn-down.sh to use the "setpci" method.
>> Hotkeys are detected, showkey -s returns 0xe0 0x4c 0xe0 0xcc for Fn+F5
>> and 0xe0 0x54 0xe0 0xd4 for Fn+F6.
>> When the hotkeys are triggered, there is no brightness change but the
>> KDE notification pops up with 3 or 4 levels.
>>
>> [X.] Other notes
>> $ ls /sys/class/backlight/
>> acpi_video0  acpi_video1  intel_backlight
>>
>> $ cat /sys/class/backlight/intel_backlight/max_brightness
>> 2583660
>>
>> $ cat /sys/class/backlight/intel_backlight/brightness
>> 121584
> With v3.12, does the intel_backlight interface work?
> You can verify this by echoing some value to the brightness file and see
> if it has any effect. The value can be echoed is 0 - max_brightness. Be
> careful with very small values, it will black your screen.
>
> If it works, you can specify intel_backlight as the control interface
> for X by creating a xorg.conf file like this:
> $ cat /etc/Xorg/Xorg.conf
> Section "Device"
>          Option     "Backlight"	"intel_backlight"
> 	Identifier  "Card0"
> 	Driver      "intel"
> 	BusID       "PCI:0:2:0"
> EndSection

The intel_backlight interface does work, by echoing a value between 0 
and 2583660.
The control interface for X also works with that addition in 
/etc/X11/xorg.conf (Kubuntu).

Wow, the issue was immediately solved by posting here. Thanks Aaron Lu!
After, (out of curiosity) what should be modified so that X 
automatically detect the correct control interface, in case of a new 
installation for example ?
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