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    Subject[PATCH v2 3/7] gpiolib: use kref in gpio_desc
    Date
    From: Bartosz Golaszewski <bgolaszewski@baylibre.com>

    GPIO descriptors are freed by consumers using gpiod_put(). The name of
    this function suggests some reference counting is going on but it's not
    true.

    Use kref to actually introduce reference counting for gpio_desc objects.
    Add a corresponding gpiod_get() helper for increasing the reference count.

    This doesn't change anything for already existing (correct) drivers but
    allows us to keep track of GPIO descs used by multiple users.

    Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
    ---
    drivers/gpio/gpiolib.c | 30 +++++++++++++++++++++++++++---
    drivers/gpio/gpiolib.h | 1 +
    include/linux/gpio/consumer.h | 1 +
    3 files changed, 29 insertions(+), 3 deletions(-)

    diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
    index 4d0106ceeba7..582425e9b449 100644
    --- a/drivers/gpio/gpiolib.c
    +++ b/drivers/gpio/gpiolib.c
    @@ -2798,6 +2798,8 @@ static int gpiod_request_commit(struct gpio_desc *desc, const char *label)
    goto done;
    }

    + kref_init(&desc->ref);
    +
    if (chip->request) {
    /* chip->request may sleep */
    spin_unlock_irqrestore(&gpio_lock, flags);
    @@ -2933,6 +2935,13 @@ void gpiod_free(struct gpio_desc *desc)
    }
    }

    +static void gpiod_free_kref(struct kref *ref)
    +{
    + struct gpio_desc *desc = container_of(ref, struct gpio_desc, ref);
    +
    + gpiod_free(desc);
    +}
    +
    /**
    * gpiochip_is_requested - return string iff signal was requested
    * @chip: controller managing the signal
    @@ -5067,18 +5076,33 @@ struct gpio_descs *__must_check gpiod_get_array_optional(struct device *dev,
    EXPORT_SYMBOL_GPL(gpiod_get_array_optional);

    /**
    - * gpiod_put - dispose of a GPIO descriptor
    - * @desc: GPIO descriptor to dispose of
    + * gpiod_put - decrease the reference count of a GPIO descriptor
    + * @desc: GPIO descriptor to unref
    *
    * No descriptor can be used after gpiod_put() has been called on it.
    */
    void gpiod_put(struct gpio_desc *desc)
    {
    if (desc)
    - gpiod_free(desc);
    + kref_put(&desc->ref, gpiod_free_kref);
    }
    EXPORT_SYMBOL_GPL(gpiod_put);

    +/**
    + * gpiod_ref - increase the reference count of a GPIO descriptor
    + * @desc: GPIO descriptor to reference
    + *
    + * Returns the same gpio_desc after increasing the reference count.
    + */
    +struct gpio_desc *gpiod_ref(struct gpio_desc *desc)
    +{
    + if (desc)
    + kref_get(&desc->ref);
    +
    + return desc;
    +}
    +EXPORT_SYMBOL_GPL(gpiod_ref);
    +
    /**
    * gpiod_put_array - dispose of multiple GPIO descriptors
    * @descs: struct gpio_descs containing an array of descriptors
    diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
    index 3e0aab2945d8..51a92c43dd55 100644
    --- a/drivers/gpio/gpiolib.h
    +++ b/drivers/gpio/gpiolib.h
    @@ -119,6 +119,7 @@ struct gpio_desc {
    const char *label;
    /* Name of the GPIO */
    const char *name;
    + struct kref ref;
    };

    int gpiod_request(struct gpio_desc *desc, const char *label);
    diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
    index bf2d017dd7b7..c7b5fb3d9d64 100644
    --- a/include/linux/gpio/consumer.h
    +++ b/include/linux/gpio/consumer.h
    @@ -81,6 +81,7 @@ struct gpio_descs *__must_check gpiod_get_array(struct device *dev,
    struct gpio_descs *__must_check gpiod_get_array_optional(struct device *dev,
    const char *con_id,
    enum gpiod_flags flags);
    +struct gpio_desc *gpiod_ref(struct gpio_desc *desc);
    void gpiod_put(struct gpio_desc *desc);
    void gpiod_put_array(struct gpio_descs *descs);

    --
    2.25.0
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