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Message-ID: <10848ac4-4b2a-4e1e-b6b8-d99cbf54c28c@gmail.com>
Date: Wed, 7 Jan 2026 11:27:44 +0530
From: tessolveupstream@...il.com
To: Bjorn Andersson <andersson@...nel.org>
Cc: konradybcio@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
conor+dt@...nel.org, linux-arm-msm@...r.kernel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 3/5] backlight: gpio: add support for multiple GPIOs
for backlight control
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@...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;
>> };
>>
>> 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
>>
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