linux-kernel - RE: [PATCH v2] pwm_backlight: Add device tree support for Low Threshold Brightness

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Message-ID: <518397C60809E147AF5323E0420B992E3E9A685B@DBDE01.ent.ti.com>
Date:	Fri, 21 Sep 2012 06:03:11 +0000
From:	"Philip, Avinash" <avinashphilip@...com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"rob@...dley.net" <rob@...dley.net>,
	"rpurdie@...ys.net" <rpurdie@...ys.net>,
	"thierry.reding@...onic-design.de" <thierry.reding@...onic-design.de>,
	"broonie@...nsource.wolfsonmicro.com" 
	<broonie@...nsource.wolfsonmicro.com>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Nori, Sekhar" <nsekhar@...com>,
	"Hebbar, Gururaja" <gururaja.hebbar@...com>
Subject: RE: [PATCH v2] pwm_backlight: Add device tree support for Low
 Threshold Brightness

Hi Stephen,

On Fri, Sep 21, 2012 at 10:46:45, Stephen Warren wrote:
> On 09/20/2012 10:51 PM, Philip, Avinash wrote:
> > Some backlights perform poorly when driven by a PWM with a short
> > duty-cycle. For such devices, the low threshold can be used to specify a
> > lower bound for the duty-cycle and should be chosen to exclude the
> > problematic range.
> > 
> > This patch adds support for an optional low-threshold-brightness
> > property.
> 
> > diff --git a/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt
> 
> >  Optional properties:
> >    - pwm-names: a list of names for the PWM devices specified in the
> >                 "pwms" property (see PWM binding[0])
> > +  - low-threshold-brightness: brightness threshold low level. Low threshold
> > +    brightness set to value so that backlight present on low end of
> > +    brightness.
> 
> For my education, why not just specify values above this value in the
> brightness-levels array; how do those two interact?

Please find details from 
https://lkml.org/lkml/2012/7/18/284

Thanks
Avinash

> It seems like any
> description of that is missing from the PWM documentation, and would be
> good to have in the DT binding too.
> 
> 

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