gpiolib: provide gpio_device_find()

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

@@ -1014,38 +1014,73 @@ 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,
 					     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;

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);