[PATCH v4 2/4] gpiolib: use kref in gpio_desc

From: Bartosz Golaszewski
Date: Thu Feb 20 2020 - 05:02:04 EST


From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>

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@xxxxxxxxxxxx>
---
drivers/gpio/gpiolib.c | 36 ++++++++++++++++++++++++++++++++---
drivers/gpio/gpiolib.h | 1 +
include/linux/gpio/consumer.h | 1 +
3 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 753283486037..42f820356279 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
@@ -5047,18 +5056,39 @@ 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)
+ return NULL;
+
+ if (!test_bit(FLAG_REQUESTED, &desc->flags)) {
+ pr_warn("gpiolib: unable to increase the reference count of unrequested GPIO descriptor\n");
+ return 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