gpio: provide gpiod_is_equal()

There are users in the kernel that directly compare raw GPIO descriptor
pointers in order to determine whether they refer to the same physical
GPIO pin. This accidentally works like this but is not guaranteed by any
API contract. Let's provide a comparator function that hides the actual
logic.

Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250407-gpiod-is-equal-v1-1-7d85f568ae6e@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Author: Bartosz Golaszewski

drivers/gpio/gpiolib.c

@@ -265,6 +265,20 @@ struct gpio_device *gpiod_to_gpio_device(struct gpio_desc *desc)
 }
 EXPORT_SYMBOL_GPL(gpiod_to_gpio_device);
 
+/**
+ * gpiod_is_equal() - Check if two GPIO descriptors refer to the same pin.
+ * @desc: Descriptor to compare.
+ * @other: The second descriptor to compare against.
+ *
+ * Returns:
+ * True if the descriptors refer to the same physical pin. False otherwise.
+ */
+bool gpiod_is_equal(struct gpio_desc *desc, struct gpio_desc *other)
+{
+	return desc == other;
+}
+EXPORT_SYMBOL_GPL(gpiod_is_equal);
+
 /**
  * gpio_device_get_base() - Get the base GPIO number allocated by this device
  * @gdev: GPIO device

include/linux/gpio/consumer.h

@@ -180,6 +180,8 @@ struct gpio_desc *devm_fwnode_gpiod_get_index(struct device *dev,
 					      enum gpiod_flags flags,
 					      const char *label);
 
+bool gpiod_is_equal(struct gpio_desc *desc, struct gpio_desc *other);
+
 #else /* CONFIG_GPIOLIB */
 
 #include <linux/bug.h>
@@ -547,6 +549,13 @@ struct gpio_desc *devm_fwnode_gpiod_get_index(struct device *dev,
 	return ERR_PTR(-ENOSYS);
 }
 
+static inline bool
+gpiod_is_equal(struct gpio_desc *desc, struct gpio_desc *other)
+{
+	WARN_ON(desc || other);
+	return false;
+}
+
 #endif /* CONFIG_GPIOLIB */
 
 #if IS_ENABLED(CONFIG_GPIOLIB) && IS_ENABLED(CONFIG_HTE)