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Date: Fri, 27 Mar 2015 16:53:48 +0100
From: Hans Petter Selasky <hps@selasky.org>
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To: "Ranjan1018 ." <214748mv@gmail.com>, 
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Subject: Re: [PATCH] Adding backlight support for the i915 driver.
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On 03/27/15 16:01, Ranjan1018 . wrote:
> This  patch exposes the backlight support  via a sysctl:
>
> set the backlight to 10%:
>
> # sysctl hw.dri.0.i915_backlight=10
>
> hw.dri.0.i915_backlight: 25 -> 10
>
> set the backlight to 50%:
>
> # sysctl hw.dri.0.i915_backlight=50
>
> hw.dri.0.i915_backlight: 10 -> 50
>
> decrease  the current backlight value:
>
> # sysctl hw.dri.0.i915_backlight=-1000
>
> hw.dri.0.i915_backlight: 50 -> 43
>
> increment the current backlight value:
>
> # sysctl hw.dri.0.i915_backlight=1000
>
> hw.dri.0.i915_backlight: 43 -> 51
>
> # sysctl hw.dri.0.i915_backlight=1000
>
> hw.dri.0.i915_backlight: 51 -> 60
>
> I am running this path on for about a week without issue.
>
> This path can be found at:
> https://github.com/maurizio-emmex/i915_backlight_freebsd
>
> I thank Elizabeth Myers, elizabeth at interlinked dot me, for the idea of
> adding the backlight support for the i915 driver and for the original patch.
>
> Regards,
> Maurizio

Maybe you want to use "CTLFLAG_RWTUN" so that it also can be set from 
/boot/loader.conf ?

--HPS