linux-kernel - Re: [PATCH v2 1/4] dt-bindings: pwm-backlight: add pwm-delay-us property

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Message-ID: <20170630112505.GA18448@amd>
Date:   Fri, 30 Jun 2017 13:25:05 +0200
From:   Pavel Machek <pavel@....cz>
To:     Enric Balletbo i Serra <enric.balletbo@...labora.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Rob Herring <robh+dt@...nel.org>,
        Richard Purdie <rpurdie@...ys.net>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Heiko Stuebner <heiko@...ech.de>, linux-pwm@...r.kernel.org,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        groeck@...omium.org, linux-rockchip@...ts.infradead.org,
        huang lin <hl@...k-chips.com>
Subject: Re: [PATCH v2 1/4] dt-bindings: pwm-backlight: add pwm-delay-us
 property

On Fri 2017-06-30 13:21:06, Enric Balletbo i Serra wrote:
> From: huang lin <hl@...k-chips.com>
> 
> Add a pwm-delay-us property to specify the delay between setting an
> initial (non-zero) PWM value and enabling the backlight, and also the
> delay between disabling the backlight and setting PWM value to 0.
> 
> Signed-off-by: huang lin <hl@...k-chips.com>
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> ---
> Changes since v1:
>  - As suggested by Daniel Thompson
>    - Do not assume power-on delay and power-off delay will be the same
> 
> v1: https://lkml.org/lkml/2017/6/28/219
> 
>  Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
> index 764db86..49b037e 100644
> --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
> +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
> @@ -17,6 +17,11 @@ Optional properties:
>                 "pwms" property (see PWM binding[0])
>    - enable-gpios: contains a single GPIO specifier for the GPIO which enables
>                    and disables the backlight (see GPIO binding[1])
> +  - pwm-delay-us: delay between setting an initial (non-zero) PWM value and
> +                  enabling the backlight, and also the delay between disabling
> +                  the backlight and setting PWM value to 0.

"Hardware needs a delay between setting an initial (non-zero) PWM and
enabling the backlight using GPIO. The 1st cell specifies this delay
in micro seconds. Hardware also needs a delay between disabing the
backlight using GPIO and setting PWM value to 0. The 2nd cell is this
delay in micro seconds."

Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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