gpiolib: provide gpiod_to_gpio_device()

Accessing struct gpio_chip backing a GPIO device is only allowed for the
actual providers of that chip.

Similarly to how we introduced gpio_device_find() in order to replace
the abused gpiochip_find(), let's introduce a counterpart to
gpiod_to_chip() that returns a reference to the GPIO device owning the
descriptor. This is done in order to later remove gpiod_to_chip()
entirely.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Peter Rosin <peda@axentia.se>
Acked-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib.c

@@ -220,6 +220,27 @@ struct gpio_chip *gpiod_to_chip(const struct gpio_desc *desc)
 }
 EXPORT_SYMBOL_GPL(gpiod_to_chip);
 
+/**
+ * gpiod_to_gpio_device() - Return the GPIO device to which this descriptor
+ *                          belongs.
+ * @desc: Descriptor for which to return the GPIO device.
+ *
+ * This *DOES NOT* increase the reference count of the GPIO device as it's
+ * expected that the descriptor is requested and the users already holds a
+ * reference to the device.
+ *
+ * Returns:
+ * Address of the GPIO device owning this descriptor.
+ */
+struct gpio_device *gpiod_to_gpio_device(struct gpio_desc *desc)
+{
+	if (!desc)
+		return NULL;
+
+	return desc->gdev;
+}
+EXPORT_SYMBOL_GPL(gpiod_to_gpio_device);
+
 /**
  * gpio_device_get_chip() - Get the gpio_chip implementation of this GPIO device
  * @gdev: GPIO device

include/linux/gpio/driver.h

@@ -785,6 +785,7 @@ int gpiochip_lock_as_irq(struct gpio_chip *gc, unsigned int offset);
 void gpiochip_unlock_as_irq(struct gpio_chip *gc, unsigned int offset);
 
 struct gpio_chip *gpiod_to_chip(const struct gpio_desc *desc);
+struct gpio_device *gpiod_to_gpio_device(struct gpio_desc *desc);
 
 #else /* CONFIG_GPIOLIB */