Re: [PATCH 2/2] backlight: pwm_bl: add configurable delay between re-enabling PWM and switching back

[Lee Jones <lee.jones@linaro.org>]

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@KARO-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
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