linux-kernel - Re: [PATCH 2/2] backlight: pwm_bl: add configurable delay between re-enabling PWM and switching backlight power on

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Date:   Mon, 30 Oct 2017 10:33:34 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Lothar Waßmann <LW@...O-electronics.de>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Jingoo Han <jingoohan1@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Pavel Machek <pavel@....cz>,
        Richard Purdie <rpurdie@...ys.net>,
        Thierry Reding <thierry.reding@...il.com>,
        devicetree@...r.kernel.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org,
        linux-pwm@...r.kernel.org
Subject: Re: [PATCH 2/2] backlight: pwm_bl: add configurable delay between
 re-enabling PWM and switching backlight power on

On Fri, 27 Oct 2017, Rob Herring wrote:

> On Thu, Oct 26, 2017 at 02:49:46PM +0200, Lothar Waßmann wrote:
> > When switching the backlight on, the LCD may need some time to adjust
> > to the configured PWM duty cycle. Add a configurable delay between
> > configuring the PWM and enabling the backlight regulator to account
> > for this.
> > 
> > Signed-off-by: Lothar Waßmann <LW@...O-electronics.de>
> > ---
> >  .../bindings/leds/backlight/pwm-backlight.txt      |  4 ++++
> >  drivers/video/backlight/pwm_bl.c                   | 22 +++++++++++++++++++---
> >  2 files changed, 23 insertions(+), 3 deletions(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
> > index 764db86..95594c3 100644
> > --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
> > +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt
> > @@ -17,6 +17,10 @@ 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])
> > +  - turn-on-delay-ms: delay in milliseconds between configuring the PWM
> > +		  and switching PWM on. This may be required to eliminate
> > +		  flicker when switching the PWM on after it has been
> > +		  disabled.
> 
> The subject talks about turning on the backlight regulator, but this 
> only talks about the PWM.

>From my understanding "switching PWM on" == enabling the regulator.

I don't see any disparity here.  Or am I missing something?

> >  [0]: Documentation/devicetree/bindings/pwm/pwm.txt
> >  [1]: Documentation/devicetree/bindings/gpio/gpio.txt

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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