linux-kernel - Re: [PATCH v1 2/2] backlight: gpio: add support for multiple GPIOs for backlight control

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Message-ID: <aVuN7zVUWJ1qsVh8@aspen.lan>
Date: Mon, 5 Jan 2026 10:09:51 +0000
From: Daniel Thompson <daniel@...cstar.com>
To: Sudarshan Shetty <tessolveupstream@...il.com>
Cc: lee@...nel.org, danielt@...nel.org, jingoohan1@...il.com, deller@....de,
	pavel@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, dri-devel@...ts.freedesktop.org,
	linux-fbdev@...r.kernel.org, linux-leds@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] backlight: gpio: add support for multiple GPIOs
 for backlight control

On Mon, Jan 05, 2026 at 02:21:20PM +0530, Sudarshan Shetty wrote:
> Extend the gpio-backlight driver to handle multiple GPIOs instead of a
> single one. This allows panels that require driving several enable pins
> to be controlled by the backlight framework.
>
> Signed-off-by: Sudarshan Shetty <tessolveupstream@...il.com>
> ---
>  drivers/video/backlight/gpio_backlight.c | 61 +++++++++++++++++-------
>  1 file changed, 45 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/video/backlight/gpio_backlight.c b/drivers/video/backlight/gpio_backlight.c
> index 728a546904b0..037e1c111e48 100644
> --- a/drivers/video/backlight/gpio_backlight.c
> +++ b/drivers/video/backlight/gpio_backlight.c
> @@ -17,14 +17,18 @@
>
>  struct gpio_backlight {
>  	struct device *dev;
> -	struct gpio_desc *gpiod;
> +	struct gpio_desc **gpiods;
> +	unsigned int num_gpios;

Why not use struct gpio_descs for this?

Once you do that, then most of the gbl->num_gpios loops can be replaced with
calls to the array based accessors.


>  };
>
>  static int gpio_backlight_update_status(struct backlight_device *bl)
>  {
>  	struct gpio_backlight *gbl = bl_get_data(bl);
> +	unsigned int i;
> +	int br = backlight_get_brightness(bl);
>
> -	gpiod_set_value_cansleep(gbl->gpiod, backlight_get_brightness(bl));
> +	for (i = 0; i < gbl->num_gpios; i++)
> +		gpiod_set_value_cansleep(gbl->gpiods[i], br);
>
>  	return 0;
>  }
> @@ -52,6 +56,7 @@ static int gpio_backlight_probe(struct platform_device *pdev)
>  	struct backlight_device *bl;
>  	struct gpio_backlight *gbl;
>  	int ret, init_brightness, def_value;
> +	unsigned int i;
>
>  	gbl = devm_kzalloc(dev, sizeof(*gbl), GFP_KERNEL);
>  	if (gbl == NULL)
> @@ -62,10 +67,22 @@ static int gpio_backlight_probe(struct platform_device *pdev)
>
>  	def_value = device_property_read_bool(dev, "default-on");
>
> -	gbl->gpiod = devm_gpiod_get(dev, NULL, GPIOD_ASIS);
> -	if (IS_ERR(gbl->gpiod))
> -		return dev_err_probe(dev, PTR_ERR(gbl->gpiod),
> -				     "The gpios parameter is missing or invalid\n");
> +	gbl->num_gpios = gpiod_count(dev, NULL);
> +	if (gbl->num_gpios == 0)
> +		return dev_err_probe(dev, -EINVAL,
> +			"The gpios parameter is missing or invalid\n");
> +	gbl->gpiods = devm_kcalloc(dev, gbl->num_gpios, sizeof(*gbl->gpiods),
> +				   GFP_KERNEL);
> +	if (!gbl->gpiods)
> +		return -ENOMEM;

This is definitely easier if you simply use devm_get_array().


> +
> +	for (i = 0; i < gbl->num_gpios; i++) {
> +		gbl->gpiods[i] =
> +			devm_gpiod_get_index(dev, NULL, i, GPIOD_ASIS);
> +		if (IS_ERR(gbl->gpiods[i]))
> +			return dev_err_probe(dev, PTR_ERR(gbl->gpiods[i]),
> +					"Failed to get GPIO at index %u\n", i);
> +	}
>
>  	memset(&props, 0, sizeof(props));
>  	props.type = BACKLIGHT_RAW;
> @@ -78,22 +95,34 @@ static int gpio_backlight_probe(struct platform_device *pdev)
>  	}
>
>  	/* Set the initial power state */
> -	if (!of_node || !of_node->phandle)
> +	if (!of_node || !of_node->phandle) {
>  		/* Not booted with device tree or no phandle link to the node */
>  		bl->props.power = def_value ? BACKLIGHT_POWER_ON
> -					    : BACKLIGHT_POWER_OFF;
> -	else if (gpiod_get_value_cansleep(gbl->gpiod) == 0)
> -		bl->props.power = BACKLIGHT_POWER_OFF;
> -	else
> -		bl->props.power = BACKLIGHT_POWER_ON;
> +						    : BACKLIGHT_POWER_OFF;
> +	} else {
> +		bool all_high = true;
> +
> +		for (i = 0; i < gbl->num_gpios; i++) {
> +			if (gpiod_get_value_cansleep(gbl->gpiods[i]) != 0) {

Why is there a != here?


> +				all_high = false;
> +				break;
> +			}
> +		}
> +
> +		bl->props.power =
> +			all_high ? BACKLIGHT_POWER_ON :  BACKLIGHT_POWER_OFF;
> +	}
>
>  	bl->props.brightness = 1;
>
>  	init_brightness = backlight_get_brightness(bl);
> -	ret = gpiod_direction_output(gbl->gpiod, init_brightness);
> -	if (ret) {
> -		dev_err(dev, "failed to set initial brightness\n");
> -		return ret;
> +
> +	for (i = 0; i < gbl->num_gpios; i++) {
> +		ret = gpiod_direction_output(gbl->gpiods[i], init_brightness);
> +		if (ret)
> +			return dev_err_probe(dev, ret,
> +					"failed to set gpio %u direction\n",
> +					i);
>  	}
>
>  	platform_set_drvdata(pdev, bl);


Daniel.