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

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Message-ID: <aWe-QA_grqNwnE4n@aspen.lan>
Date: Wed, 14 Jan 2026 16:03:12 +0000
From: Daniel Thompson <daniel@...cstar.com>
To: 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 Tue, Jan 13, 2026 at 12:47:26PM +0530, tessolveupstream@...il.com wrote:
>
>
> On 05-01-2026 15:39, Daniel Thompson wrote:
> > 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.
> >
>
> Based on your feedback, I have updated the implementation to use
> struct gpio_descs and array-based accessors, as recommended like
> below:
>
> git diff drivers/video/backlight/gpio_backlight.c
> diff --git a/drivers/video/backlight/gpio_backlight.c b/drivers/video/backlight/gpio_backlight.c
> index 037e1c111e48..e99d7a9dc670 100644
> --- a/drivers/video/backlight/gpio_backlight.c
> +++ b/drivers/video/backlight/gpio_backlight.c
> @@ -14,22 +14,37 @@
>  #include <linux/platform_device.h>
>  #include <linux/property.h>
>  #include <linux/slab.h>
> +#include <linux/bitmap.h>
>
>  struct gpio_backlight {
>         struct device *dev;
> -       struct gpio_desc **gpiods;
> +       struct gpio_descs *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;
> +       unsigned int n = gbl->num_gpios;
>         int br = backlight_get_brightness(bl);
> +       unsigned long *value_bitmap;
> +       int words = BITS_TO_LONGS(n);
> +
> +       value_bitmap = kcalloc(words, sizeof(unsigned long), GFP_KERNEL);

Not sure you need a kcalloc() here. If you want to support more than 32
GPIOs then you can pre-allocate space with a devm_kcalloc() in the probe
method rather than reallocate every time it is used.

To be honest I don't really mind putting a hard limit on the maximum
gpl->num_gpios (so you can just use a local variable) and having no
allocation at all.


> Could you please share your thoughts on whether this approach
> aligns with your expectations?

Looks like it is going in the right direction, yes.


Daniel.