linux-kernel - Re: [PATCH] backlight: gpio-backlight: use default-on on GPIO request

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Message-ID: <147193eb17eabe97602b85bc88ad4206@agner.ch>
Date:	Wed, 16 Dec 2015 21:08:37 -0800
From:	Stefan Agner <stefan@...er.ch>
To:	jingoohan1@...il.com, lee.jones@...aro.org
Cc:	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] backlight: gpio-backlight: use default-on on GPIO request

Hi,

Any comment on this? I still think it is a valuable change...

--
Stefan

On 2015-10-23 16:44, Stefan Agner wrote:
> There are situations where the backlight should be on at boot time
> (e.g. if the boot loader already turned the display on). The DT
> bindings specify the "default-on" property for that purpose.
> Currently, the initial state of the GPIO at request time is always
> set to logical off (high or low depending on whether it is an
> active high or low GPIO). Since the GPIO is requested as an output,
> the GPIO will be driven low for a short period of time, which leads
> to a flickering display in the above use-case.
> 
> Initialize the GPIO depending on the default-on property to be
> logical on or off.
> 
> Signed-off-by: Stefan Agner <stefan@...er.ch>
> ---
>  drivers/video/backlight/gpio_backlight.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/video/backlight/gpio_backlight.c
> b/drivers/video/backlight/gpio_backlight.c
> index 5fbbc2e..1813441 100644
> --- a/drivers/video/backlight/gpio_backlight.c
> +++ b/drivers/video/backlight/gpio_backlight.c
> @@ -89,6 +89,7 @@ static int gpio_backlight_probe(struct platform_device *pdev)
>  	struct backlight_device *bl;
>  	struct gpio_backlight *gbl;
>  	struct device_node *np = pdev->dev.of_node;
> +	unsigned long flags = GPIOF_DIR_OUT;
>  	int ret;
>  
>  	if (!pdata && !np) {
> @@ -114,9 +115,12 @@ static int gpio_backlight_probe(struct
> platform_device *pdev)
>  		gbl->def_value = pdata->def_value;
>  	}
>  
> -	ret = devm_gpio_request_one(gbl->dev, gbl->gpio, GPIOF_DIR_OUT |
> -				    (gbl->active ? GPIOF_INIT_LOW
> -						 : GPIOF_INIT_HIGH),
> +	if (gbl->active)
> +		flags |= gbl->def_value ? GPIOF_INIT_HIGH : GPIOF_INIT_LOW;
> +	else
> +		flags |= gbl->def_value ? GPIOF_INIT_LOW : GPIOF_INIT_HIGH;
> +
> +	ret = devm_gpio_request_one(gbl->dev, gbl->gpio, flags,
>  				    pdata ? pdata->name : "backlight");
>  	if (ret < 0) {
>  		dev_err(&pdev->dev, "unable to request GPIO\n");
--
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