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Subject[PATCH 10/15 v4] gpio: Add devm_gpiod_unhinge()
Date
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 v3->v4:
- Pass a pointer to a pointer &desc instead of just the
descriptor pointer: it is the memory address storing the
pointer that hooks into resource management.
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 f9591b5c9748..0acc2cc6e868 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);
+ /*
+ * 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();
--
2.19.2
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