Re: [PATCH] acpi-video: Add disable_native_backlight quirk for Dell XPS15 L521X

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 11-01-15 07:16, Matthew Garrett wrote:
> On Mon, Jan 05, 2015 at 08:57:04AM +0100, Hans de Goede wrote:
>> The L521X variant of the Dell XPS15 has integrated nvidia graphics, and
>> backlight control does not work properly when using the native interfaces.
>
> I'm not convinced that the assessment of this bug is correct. Is the
> system using the nvidia graphics device?

I do not know.

> If so, why is userspace writing to the intel backlight device?

Userspace is writing to the intel_backlight device because it is the
only one present under /sys/class/backlight, as we disable acpi-video
on win8 ready laptops by default now.

What this commit does is disable the disabling of acpi-video, and
after that userspace will see an acpi_video0 backlight under
/sys/class/backlight, use that and then things work, this has been
confirmed by the bug reporter.

The commit message may not be 100% accurate, although I believe this is
related to the laptop having nvidia graphics, but the code / fix is correct
regardless.

Regards,

Hans