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

From: Rob Herring
Date: Fri Oct 27 2017 - 10:38:29 EST


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@xxxxxxxxxxxxxxxxxxx>
> ---
> .../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.

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