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

[Aaron Lu <aaron.lu@intel.com>]

On 12/03/2013 06:10 PM, Guillaume Millet wrote:
> 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 ?

Please file a bug to https://bugzilla.kernel.org, choose
ACPI-Power/Video category.

Please provide these information when filing the bug:
1 attach dmesg.
2 attach acpidump output.
3 attach dmidecode output.
4 of those backlight control interfaces, which works and which don't.
5 attach /var/log/Xorg.0.log when you do not use the customized xorg.conf,
  I want to know which interface is picked up by X driver by default.

Thanks,
Aaron
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