linux-kernel - Re: [PATCH 2/2] leds: gpio: Add devlinks between the gpio consumed and the gpio leds device

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Date: Wed, 21 Feb 2024 23:45:31 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Herve Codina <herve.codina@...tlin.com>, Saravana Kannan <saravanak@...gle.com>
Cc: Bartosz Golaszewski <brgl@...ev.pl>, Pavel Machek <pavel@....cz>, Lee Jones <lee@...nel.org>, 
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-leds@...r.kernel.org, Luca Ceresoli <luca.ceresoli@...tlin.com>, 
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 2/2] leds: gpio: Add devlinks between the gpio consumed
 and the gpio leds device

Saravana needs to look at this patch too, so I am top-posting.

Yours,
Linus Walleij

On Tue, Feb 20, 2024 at 12:11 PM Herve Codina <herve.codina@...tlincom> wrote:

> When a gpio is removed, the gpio leds consumer need to be removed first.
> This dependency consumer/supplier can be described by devlink links.
> In case of device-tree, even if some devlinks are created due to the
> presence of gpio phandles in the gpio leds children, these links do not
> help in removing the gpio leds device (i.e. the real consumer) before
> the consumed gpio.
> We can reach cases where the gpio are no more present and the gpio leds
> driver continue to have leds using these gpio.
> Further more, when the gpio come back, the gpio leds still use the old
> removed one.
>
> Indeed, the gpio are consumed by the parent of the consumer used in the
> devlink creation due to phandles. A link is missing between the gpio and
> the real gpio consumer, the gpio leds device itself.
>
> Use the newly introduced gpiod_device_add_link() to create this
> missing link between the gpio leds devices and the gpios.
> With that done, if a gpio is removed, the gpio leds is removed and the
> resources are correctly released.
>
> Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> ---
>  drivers/leds/leds-gpio.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
>
> diff --git a/drivers/leds/leds-gpio.c b/drivers/leds/leds-gpio.c
> index 83fcd7b6afff..b3ec8ecbe5da 100644
> --- a/drivers/leds/leds-gpio.c
> +++ b/drivers/leds/leds-gpio.c
> @@ -150,6 +150,7 @@ static struct gpio_leds_priv *gpio_leds_create(struct device *dev)
>  {
>         struct fwnode_handle *child;
>         struct gpio_leds_priv *priv;
> +       struct device_link *link;
>         int count, ret;
>
>         count = device_get_child_node_count(dev);
> @@ -197,6 +198,20 @@ static struct gpio_leds_priv *gpio_leds_create(struct device *dev)
>                 /* Set gpiod label to match the corresponding LED name. */
>                 gpiod_set_consumer_name(led_dat->gpiod,
>                                         led_dat->cdev.dev->kobj.name);
> +
> +               /*
> +                * Create a link between the GPIO and the gpio-leds device.
> +                * This allow to have a relationship between the gpio used and
> +                * the gpio-leds device in order to automatically remove the
> +                * gpio-leds device (consumer) when a GPIO (supplier) is removed.
> +                */
> +               link = gpiod_device_add_link(dev, led_dat->gpiod,
> +                                            DL_FLAG_AUTOREMOVE_CONSUMER);
> +               if (IS_ERR(link)) {
> +                       fwnode_handle_put(child);
> +                       return ERR_CAST(link);
> +               }
> +
>                 priv->num_leds++;
>         }
>
> --
> 2.43.0
>