Comment 12 for bug 954661

Kamal,

I booted with acpi_backlight=vendor, and that makes things worse out of the
box. At max brightness (what it boots by default) no discernable
difference. Then when the screen goes into idle after a few minutes not on
AC it starts flickering at me violently. The same thing happens if I
manually hit the brightness down keys. The lower the brightness the more
aggressive the flicker until I go to zero brightness when the flicker goes
away.

Also, it's worth noting, booting with that option created a dell_backlight
in /sys/class/backlight as well as that intel_backlight.

This is the same type of flicker that happens if I manually set any value
(that I tried) in /sys/class/backlight/intel_backlight/brightness other
than 0 or 4882.

On Tue, Apr 10, 2012 at 16:33, Kamal Mostafa <email address hidden> wrote:

> Mario, from your comment #5, it sounds to me like the problem may be due
> to there being two /sys/class/backlight interfaces present (acpi_video0
> and intel_backlight). Mario & Daniel, you might try booting with the
> kernel boot parameter "acpi_backlight=vendor" which should disable
> acpi_video0 leaving only intel_backlight. Does that improve any of the
> behaviors you're seeing (or make them worse)?
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/954661
>
> Title:
> backlight brightness not adjustable by default on Dell XPS 13
>
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--
Mario Limonciello
<email address hidden>