Re: [PATCH v10 3/5] backlight: gpio: add support for multiple GPIOs for backlight control

[tessolveupstream@gmail.com]

On 05-01-2026 21:08, Bjorn Andersson wrote:
> On Tue, Dec 30, 2025 at 06:32:25PM +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.
> 
> Can you please elaborate on the problem described here. Preferrably in
> the form described in
> https://docs.kernel.org/process/submitting-patches.html#describe-your-changes,
> i.e. start with your problem description, then a description of your
> solution.
> 
> What does it mean for a backlight device to have multiple enable GPIOs?
> 
> 
> PS. The associated binding patch needs to be merged before the
> DeviceTree (dts) changes can be merged, but it would be more efficient
> to upstream them separately - as each set of reviewers could focus on
> their part and you could update the patches based on the feedback from
> each part.
>

Initially, I had included the gpio-backlight driver and binding changes 
together in the v10 patch series. Later I separated these 
gpio-backlight changes and submitted them as individual patches to the respective maintainers.Here is the link to the updated patch series:
https://lore.kernel.org/all/20260105085120.230862-1-tessolveupstream@gmail.com/T/#t
 
> Regards,
> Bjorn
> 
>>
>> Signed-off-by: Sudarshan Shetty <tessolveupstream@gmail.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;
>>  };
>>  
>>  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;
>> +
>> +	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) {
>> +				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);
>> -- 
>> 2.34.1
>>