gpiolib: use gpiochip_dup_line_label() in for_each helpers

Rework for_each_requested_gpio_in_range() to use the new helper to
retrieve a dynamically allocated copy of the descriptor label and free
it at the end of each iteration. We need to leverage the CLASS()'
destructor to make sure that the label is freed even when breaking out
of the loop.
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/gpio/driver.h

@@ -534,17 +534,38 @@ struct gpio_chip {
 const char *gpiochip_is_requested(struct gpio_chip *gc, unsigned int offset);
 char *gpiochip_dup_line_label(struct gpio_chip *gc, unsigned int offset);
 
+
+struct _gpiochip_for_each_data {
+	const char **label;
+	unsigned int *i;
+};
+
+DEFINE_CLASS(_gpiochip_for_each_data,
+	     struct _gpiochip_for_each_data,
+	     if (*_T.label) kfree(*_T.label),
+	     ({
+		struct _gpiochip_for_each_data _data = { label, i };
+		*_data.i = 0;
+		_data;
+	     }),
+	     const char **label, int *i)
+
 /**
  * for_each_requested_gpio_in_range - iterates over requested GPIOs in a given range
- * @chip:	the chip to query
- * @i:		loop variable
- * @base:	first GPIO in the range
- * @size:	amount of GPIOs to check starting from @base
- * @label:	label of current GPIO
+ * @_chip:	the chip to query
+ * @_i:		loop variable
+ * @_base:	first GPIO in the range
+ * @_size:	amount of GPIOs to check starting from @base
+ * @_label:	label of current GPIO
  */
-#define for_each_requested_gpio_in_range(chip, i, base, size, label)			\
-	for (i = 0; i < size; i++)							\
-		if ((label = gpiochip_is_requested(chip, base + i)) == NULL) {} else
+#define for_each_requested_gpio_in_range(_chip, _i, _base, _size, _label)		\
+	for (CLASS(_gpiochip_for_each_data, _data)(&_label, &_i);			\
+	     *_data.i < _size;								\
+	     (*_data.i)++, kfree(*(_data.label)), *_data.label = NULL)			\
+		if ((*_data.label =							\
+			gpiochip_dup_line_label(_chip, _base + *_data.i)) == NULL) {}	\
+		else if (IS_ERR(*_data.label)) {}					\
+		else
 
 /* Iterates over all requested GPIO of the given @chip */
 #define for_each_requested_gpio(chip, i, label)						\