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

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

[Stefan Agner]

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@agner.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");
-- 
2.6.2

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

[Stefan Agner]

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@agner.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");

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

[Lee Jones]

On Fri, 23 Oct 2015, 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@agner.ch>
> ---
>  drivers/video/backlight/gpio_backlight.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)

Applied, thanks.

> 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");

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog