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

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Message-ID: <505BF83D.8040201@wwwdotorg.org>
Date:	Thu, 20 Sep 2012 23:16:45 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	"Philip, Avinash" <avinashphilip@...com>
CC:	grant.likely@...retlab.ca, rob.herring@...xeda.com,
	rob@...dley.net, rpurdie@...ys.net,
	thierry.reding@...onic-design.de,
	broonie@...nsource.wolfsonmicro.com, shawn.guo@...aro.org,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, nsekhar@...com,
	gururaja.hebbar@...com
Subject: Re: [PATCH v2] pwm_backlight: Add device tree support for Low Threshold
 Brightness

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? 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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