[PATCH v3 03/11] gpiolib: provide gpio_device_find()

Bartosz Golaszewski
2023-09-15T15:03:47Z

gpiochip_find() is wrong and its kernel doc is misleading as the
function doesn't return a reference to the gpio_chip but just a raw
pointer. The chip itself is not guaranteed to stay alive, in fact it can
be deleted at any point. Also: other than GPIO drivers themselves,
nobody else has any business accessing gpio_chip structs.

Provide a new gpio_device_find() function that returns a real reference
to the opaque gpio_device structure that is guaranteed to stay alive for
as long as there are active users of it.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
---
drivers/gpio/gpiolib.c | 71 +++++++++++++++++++++++++++----------
include/linux/gpio/driver.h | 3 ++
2 files changed, 56 insertions(+), 18 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index f84ad54d8dbd..0371d23f0a46 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1014,16 +1014,10 @@ void gpiochip_remove(struct gpio_chip *gc)
}
EXPORT_SYMBOL_GPL(gpiochip_remove);

-/**
- * gpiochip_find() - iterator for locating a specific gpio_chip
- * @data: data to pass to match function
- * @match: Callback function to check gpio_chip
+/*
+ * FIXME: This will be removed soon.
*
- * Similar to bus_find_device. It returns a reference to a gpio_chip as
- * determined by a user supplied @match callback. The callback should return
- * 0 if the device doesn't match and non-zero if it does. If the callback is
- * non-zero, this function will return to the caller and not iterate over any
- * more gpio_chips.
+ * This function is depracated, don't use.
*/
struct gpio_chip *gpiochip_find(void *data,
int (*match)(struct gpio_chip *gc,
@@ -1031,21 +1025,62 @@ struct gpio_chip *gpiochip_find(void *data,
{
struct gpio_device *gdev;
struct gpio_chip *gc = NULL;
- unsigned long flags;

- spin_lock_irqsave(&gpio_lock, flags);
- list_for_each_entry(gdev, &gpio_devices, list)
- if (gdev->chip && match(gdev->chip, data)) {
- gc = gdev->chip;
- break;
- }
-
- spin_unlock_irqrestore(&gpio_lock, flags);
+ gdev = gpio_device_find(data, match);
+ if (gdev) {
+ gc = gdev->chip;
+ gpio_device_put(gdev);
+ }

return gc;
}
EXPORT_SYMBOL_GPL(gpiochip_find);

+/**
+ * gpio_device_find() - find a specific GPIO device
+ * @data: data to pass to match function
+ * @match: Callback function to check gpio_chip
+ *
+ * Returns:
+ * New reference to struct gpio_device.
+ *
+ * Similar to bus_find_device(). It returns a reference to a gpio_device as
+ * determined by a user supplied @match callback. The callback should return
+ * 0 if the device doesn't match and non-zero if it does. If the callback
+ * returns non-zero, this function will return to the caller and not iterate
+ * over any more gpio_devices.
+ *
+ * The callback takes the GPIO chip structure as argument. During the execution
+ * of the callback function the chip is protected from being freed. TODO: This
+ * actually has yet to be implemented.
+ *
+ * If the function returns non-NULL, the returned reference must be freed by
+ * the caller using gpio_device_put().
+ */
+struct gpio_device *gpio_device_find(void *data,
+ int (*match)(struct gpio_chip *gc,
+ void *data))
+{
+ struct gpio_device *gdev;
+
+ /*
+ * Not yet but in the future the spinlock below will become a mutex.
+ * Annotate this function before anyone tries to use it in interrupt
+ * context like it happened with gpiochip_find().
+ */
+ might_sleep();
+
+ guard(spinlock_irqsave)(&gpio_lock);
+
+ list_for_each_entry(gdev, &gpio_devices, list) {
+ if (gdev->chip && match(gdev->chip, data))
+ return gpio_device_get(gdev);
+ }
+
+ return NULL;
+}
+EXPORT_SYMBOL_GPL(gpio_device_find);
+
static int gpiochip_match_name(struct gpio_chip *gc, void *data)
{
const char *name = data;
diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
index 1cedbc3d3200..6ad1f1a8ef2e 100644
--- a/include/linux/gpio/driver.h
+++ b/include/linux/gpio/driver.h
@@ -608,6 +608,9 @@ int devm_gpiochip_add_data_with_key(struct device *dev, struct gpio_chip *gc,
struct gpio_chip *gpiochip_find(void *data,
int (*match)(struct gpio_chip *gc, void *data));

+struct gpio_device *gpio_device_find(void *data,
+ int (*match)(struct gpio_chip *gc, void *data));
+
struct gpio_device *gpio_device_get(struct gpio_device *gdev);
void gpio_device_put(struct gpio_device *gdev);

--
2.39.2