gpio: provide for_each_hwgpio()

We only provide iterators for requested GPIOs to provider drivers. In
order to allow them to display debug information about all GPIOs, let's
provide a variant for iterating over all GPIOs.
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/gpio/driver.h

@@ -551,6 +551,21 @@ DEFINE_CLASS(_gpiochip_for_each_data,
 	     }),
 	     const char **label, int *i)
 
+/**
+ * for_each_hwgpio - Iterates over all GPIOs for given chip.
+ * @_chip: Chip to iterate over.
+ * @_i: Loop counter.
+ * @_label: Place to store the address of the label if the GPIO is requested.
+ *          Set to NULL for unused GPIOs.
+ */
+#define for_each_hwgpio(_chip, _i, _label) \
+	for (CLASS(_gpiochip_for_each_data, _data)(&_label, &_i); \
+	     *_data.i < _chip->ngpio; \
+	     (*_data.i)++, kfree(*(_data.label)), *_data.label = NULL) \
+		if (IS_ERR(*_data.label = \
+			gpiochip_dup_line_label(_chip, *_data.i))) {} \
+		else
+
 /**
  * for_each_requested_gpio_in_range - iterates over requested GPIOs in a given range
  * @_chip:	the chip to query