[Kde-hardware-devel] Powerdevil: brightness keys change values in incorrect file

[Sparhawk]

Hi, I've been chatting with bcooksley at the KDE forums [1], and he/she
suggested that I post here with my question.

I have a Dell XPS 17 L702X, running Kubuntu 13.04 (KDE 4.10.2). In the
update from 12.10 to 13.04, changing the brightness no longer works as
expected. I get the same results using the brightness keys (which shows
feedback with the OSD) or using xbacklight.

When `/etc/default/grub` contains
    GRUB_CMDLINE_LINUX_DEFAULT="acpi_backlight=vendor"

`/sys/class/backlight/` contains `dell_backlight` and `intel_backlight`.
Pressing the brightness keys modifies the value in
`dell_backlight/brightness`, but does nothing to the display . However,
if I manually modify the values in `intel_backlight/brightness`, the
backlight changes as expected.

OTOH, If I modify `/etc/default/grub` to contain
    GRUB_CMDLINE_LINUX_DEFAULT=""

`/sys/class/backlight/` now contains `acpi_video0`, `acpi_video1` and
`intel_backlight`. Now, the brightness keys modify
`acpi_video1/brightness`, and the display's brightness alters.

Even though this does work somewhat, setting `acpi_backlight=vendor` in
Kubuntu 12.10 gave me more control over the backlight. For example, I
could reduce the backlight down to 0% and have the screen turn off.
Without this grub option, I can reduce `acpi_video1/brightness` to 0
with the brightness keys, but the backlight is still on (dimly). Hence,
it seems that the ideal situation is for the brightness keys to modify
intel_backlight instead of acpi_video1. Is this possible?

Cheers, and thanks in advance.
Sparhawk.

[1] http://forum.kde.org/viewtopic.php?f=63&t=110984