Multiple video backlight devices on Dell laptop

Multiple video backlight devices on Dell laptop

[Bradley Baetz]

Hi,

I have a Dell Vostro 3560 laptop, with hybrid graphics (intel + radeon).

This exposes 3 backlight devices - acpi_video0, acpi_video1, and
intel_backlight. Only the intel_backlight/brightness file actually
changes the backlight. Is this a kernel bug, or should userspace
'know' which backlight file to use based on which graphics device is
active? XFCE picks the first one it finds (acpi_video0), which doesn't
work.

I was using acpi_backlight=vendor, but some recent changes to memory
allocation seem to have exposed that that SMM method is not safe to
use with EFI... (see http://marc.info/?t=138811462300004&r=1&w=2)

I've uploaded my ACPI tables to http://members.optusnet.com.au/bbaetz1/acpi.tgz

Bradley

Re: Multiple video backlight devices on Dell laptop

[Aaron Lu]

On 01/11/2014 11:22 AM, Bradley Baetz wrote:
> Hi,
> 
> I have a Dell Vostro 3560 laptop, with hybrid graphics (intel + radeon).
> 
> This exposes 3 backlight devices - acpi_video0, acpi_video1, and
> intel_backlight. Only the intel_backlight/brightness file actually
> changes the backlight. Is this a kernel bug, or should userspace
> 'know' which backlight file to use based on which graphics device is
> active? XFCE picks the first one it finds (acpi_video0), which doesn't
> work.

Solving it from userspace:
You can specify which backlight interface to use by editing /etc/xorg.conf:
 Section "Device"
    Identifier  "Intel Graphics"
    Driver      "intel"
    Option      "AccelMethod"     "sna"
    Option      "Backlight"       "intel_backlight" # use your backlight that works here
    Driver      "intel"
    BusID       "PCI:0:2:0"
 EndSection

See https://wiki.archlinux.org/index.php/Backlight

solving it from kernel space:
Since the firmware claims support of win8, you can forget the
acpi_backlight=vendor cmdline option and just use video.use_native_backlight=1.

Hope it helps.
-Aaron

Re: Multiple video backlight devices on Dell laptop

[Bradley Baetz]

On Tue, Jan 14, 2014 at 1:49 PM, Aaron Lu <aaron.lu@intel.com> wrote:
> On 01/11/2014 11:22 AM, Bradley Baetz wrote:
>> Hi,
>>
>> I have a Dell Vostro 3560 laptop, with hybrid graphics (intel + radeon).
>>
>> This exposes 3 backlight devices - acpi_video0, acpi_video1, and
>> intel_backlight. Only the intel_backlight/brightness file actually
>> changes the backlight. Is this a kernel bug, or should userspace
>> 'know' which backlight file to use based on which graphics device is
>> active? XFCE picks the first one it finds (acpi_video0), which doesn't
>> work.
>
> Solving it from userspace:
> You can specify which backlight interface to use by editing /etc/xorg.conf:
>  Section "Device"
>     Identifier  "Intel Graphics"
>     Driver      "intel"
>     Option      "AccelMethod"     "sna"
>     Option      "Backlight"       "intel_backlight" # use your backlight that works here
>     Driver      "intel"
>     BusID       "PCI:0:2:0"
>  EndSection
>
> See https://wiki.archlinux.org/index.php/Backlight
>
> solving it from kernel space:
> Since the firmware claims support of win8, you can forget the
> acpi_backlight=vendor cmdline option and just use video.use_native_backlight=1.

Thanks, that commandline option works on 3.13-rc.

Bradley