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Subject: Re: [PATCH 11/15 v3] gpio: Add devm_gpiod_unhinge()
To:     Linus Walleij <linus.walleij@linaro.org>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Mark Brown <broonie@kernel.org>
Cc:     linux-kernel@vger.kernel.org,
        Charles Keepax <ckeepax@opensource.cirrus.com>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>
From:   Marek Szyprowski <m.szyprowski@samsung.com>
Message-ID: <0179c784-137d-b37a-1b93-cf2f957730a8@samsung.com>
Date:   Wed, 5 Dec 2018 15:34:01 +0100
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References: <20181205124721.26624-1-linus.walleij@linaro.org>
        <CGME20181205124846epcas3p1219065f3ca6c30f6e594a31ff3e72636@epcas3p1.samsung.com>
        <20181205124721.26624-12-linus.walleij@linaro.org>
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Hi Linus,

On 2018-12-05 13:47, Linus Walleij wrote:
> This adds a function named devm_gpiod_unhinge() that removes
> the resource management from a GPIO descriptor.
>
> I am not sure if this is the best anglosaxon name for the
> function, no other managed resources have an equivalent
> currently, but I chose "unhinge" as the closest intuitive
> thing I could imagine that fits Rusty Russell's API design
> criterions "the obvious use is the correct one" and
> "the name tells you how to use it".
>
> The idea came out of a remark from Mark Brown that it should
> be possible to handle over management of a resource from
> devres to the regulator core, and indeed we can do that.
>
> Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
> ChangeLog v2->v3:
> - Make sure to bail out of gpiod_unhinge() if the descritor
>   passed in is NULL or an error pointer.
> - Accept of devres_destroy() returns -ENOENT: if we have
>   nonexclusive GPIOs, we may attempt to remove resource
>   management from the same descriptor multiple times.
> ChangeLog v1->v2:
> - New patch to be able to hand over GPIO descriptors to
>   the regulator core.
> - Mark: feel free to apply this to the regulator tree with
>   the regulator tree with the rest.
> ---
>  Documentation/driver-model/devres.txt |  1 +
>  drivers/gpio/gpiolib-devres.c         | 30 +++++++++++++++++++++++++++
>  include/linux/gpio/consumer.h         | 10 +++++++++
>  3 files changed, 41 insertions(+)
>
> diff --git a/Documentation/driver-model/devres.txt b/Documentation/driver-model/devres.txt
> index 43681ca0837f..fc4cc24dfb97 100644
> --- a/Documentation/driver-model/devres.txt
> +++ b/Documentation/driver-model/devres.txt
> @@ -254,6 +254,7 @@ GPIO
>    devm_gpiod_get_index_optional()
>    devm_gpiod_get_optional()
>    devm_gpiod_put()
> +  devm_gpiod_unhinge()
>    devm_gpiochip_add_data()
>    devm_gpiochip_remove()
>    devm_gpio_request()
> diff --git a/drivers/gpio/gpiolib-devres.c b/drivers/gpio/gpiolib-devres.c
> index a57e968025a8..e9a17ec4de02 100644
> --- a/drivers/gpio/gpiolib-devres.c
> +++ b/drivers/gpio/gpiolib-devres.c
> @@ -346,6 +346,36 @@ void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
>  }
>  EXPORT_SYMBOL(devm_gpiod_put);
>  
> +/**
> + * devm_gpiod_unhinge - Remove resource management from a gpio descriptor
> + * @dev:	GPIO consumer
> + * @desc:	GPIO descriptor to remove resource management from
> + *
> + * Remove resource management from a GPIO descriptor. This is needed when
> + * you want to hand over lifecycle management of a descriptor to another
> + * mechanism.
> + */
> +
> +void devm_gpiod_unhinge(struct device *dev, struct gpio_desc *desc)
> +{
> +	int ret;
> +
> +	if (IS_ERR_OR_NULL(desc))
> +		return;
> +	ret = devres_destroy(dev, devm_gpiod_release,
> +			     devm_gpiod_match, desc);

    devres_destroy(dev, devm_gpiod_release, devm_gpiod_match, &desc);

> +	/*
> +	 * If the GPIO descriptor is requested as nonexclusive, we
> +	 * may call this function several times on the same descriptor
> +	 * so it is OK if devres_destroy() returns -ENOENT.
> +	 */
> +	if (ret == -ENOENT)
> +		return;
> +	/* Anything else we should warn about */
> +	WARN_ON(ret);
> +}
> +EXPORT_SYMBOL(devm_gpiod_unhinge);
> +
>  /**
>   * devm_gpiod_put_array - Resource-managed gpiod_put_array()
>   * @dev:	GPIO consumer
> diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
> index 348885f2f3d3..8aebcf822082 100644
> --- a/include/linux/gpio/consumer.h
> +++ b/include/linux/gpio/consumer.h
> @@ -104,6 +104,7 @@ struct gpio_descs *__must_check
>  devm_gpiod_get_array_optional(struct device *dev, const char *con_id,
>  			      enum gpiod_flags flags);
>  void devm_gpiod_put(struct device *dev, struct gpio_desc *desc);
> +void devm_gpiod_unhinge(struct device *dev, struct gpio_desc *desc);
>  void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs);
>  
>  int gpiod_get_direction(struct gpio_desc *desc);
> @@ -249,6 +250,15 @@ static inline void gpiod_put(struct gpio_desc *desc)
>  	WARN_ON(1);
>  }
>  
> +static inline void devm_gpiod_unhinge(struct device *dev,
> +				      struct gpio_desc *desc)
> +{
> +	might_sleep();
> +
> +	/* GPIO can never have been requested */
> +	WARN_ON(1);
> +}
> +
>  static inline void gpiod_put_array(struct gpio_descs *descs)
>  {
>  	might_sleep();

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland