linux-kernel - Re: DT support for Low threshold brightness in backlight.

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Date:	Mon, 23 Jul 2012 10:32:33 +0200
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	"Philip, Avinash" <avinashphilip@...com>
Cc:	"rpurdie@...ys.net" <rpurdie@...ys.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Nori, Sekhar" <nsekhar@...com>,
	"Hebbar, Gururaja" <gururaja.hebbar@...com>
Subject: Re: DT support for Low threshold brightness in backlight.

On Wed, Jul 18, 2012 at 02:59:32PM +0000, Philip, Avinash wrote:
> Hi,
> 
> In pwm-backlight driver low threshold brightness support in DT is not
> present. Do you have any plans in such direction?
> 
> I am planning to add support for the same but want to avoid duplication
> of work.
> 
> Below scenario describes need for it:
> On some boards panel backlight is OFF at low end of brightness scale.
> So with Low threshold brightness we can have linear scale in brightness
> (Though the actual brightness scale is changes to Low threshold
> brightness value instead of 0).
> 
> Example with Low threshold brightness
> 	pwms = <&pwm 0 50000>;
> 	brightness-levels = <0 2 4 8 16 32 64 128 255>;
> 	default-brightness-level = <6>;
> 	brightness_threshold_level = <50>;
> 
> It can also be achieved without Low threshold brightness as below
> 
> 	pwms = <&pwm 0 50000>;
> 	brightness-levels = <0 51 53 56 62 75 101 152 255>; 
> 	default-brightness-level = <6>;
> 
> But brightness-levels won't be uniformly divided.
> 
> So it is good to have low threshold DT support for backlight.
> 
> Thanks
> Avinash Philip

I have no plans to add it myself, but feel free to send a patch. There
is a corresponding field in the platform data already, so adding DT
support is probably a good idea.

Thierry

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