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

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Date:   Thu, 13 Jul 2017 09:39:54 +0200
From:   Pavel Machek <pavel@....cz>
To:     Enric Balletbo Serra <eballetbo@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        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>,
        Richard Purdie <rpurdie@...ys.net>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Linux PWM List <linux-pwm@...r.kernel.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Guenter Roeck <groeck@...omium.org>,
        "open list:ARM/Rockchip SoC..." <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 Thu 2017-07-13 09:22:15, Enric Balletbo Serra wrote:
> Rob,
> 
> 2017-07-06 20:23 GMT+02:00 Enric Balletbo Serra <eballetbo@...il.com>:
> > Hi Rob,
> >
> > 2017-07-06 19:07 GMT+02:00 Rob Herring <robh+dt@...nel.org>:
> >> On Fri, Jun 30, 2017 at 6:21 AM, Enric Balletbo i Serra
> >> <enric.balletbo@...labora.com> 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.
> >>> +                  The 1st cell is the pre-delay in micro seconds.
> >>> +                  The 2nd cell is the post-delay in micro seconds.
> >>
> >> pre and post imply a time before and after a certain event, but these
> >> are for 2 different events. These are more like an enable/on delay and
> >> disable/off delay which probably should be separate properties. What
> >> happens when we need the opposite sequence or a different sequence?
> >> Maybe some panel requires the PWM to be 0 until some time after
> >> enabling.
> >>
> 
> A second proposal, what do you think?
> 
>   - post-pwm-on-delay-us: Delay in us after setting an initial (non-zero) PWM
>                           and enabling the backlight using GPIO.

This says "PWM on", "enable GPIO", "delay". Which is not what you
want.

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

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