gpio: add gpiod_toggle_active_low()

Add possibility to toggle active-low flag of a gpio descriptor. This is
useful for compatibility code, where defaults are inverted vs DT gpio
flags or the active-low flag is taken from elsewhere.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Link: https://lore.kernel.org/r/7ce0338e01ad17fa5a227176813941b41a7c35c1.1576031637.git.mirq-linux@rere.qmqm.pl
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/gpio/gpiolib.c

@@ -3363,6 +3363,17 @@ int gpiod_is_active_low(const struct gpio_desc *desc)
 }
 EXPORT_SYMBOL_GPL(gpiod_is_active_low);
 
+/**
+ * gpiod_toggle_active_low - toggle whether a GPIO is active-low or not
+ * @desc: the gpio descriptor to change
+ */
+void gpiod_toggle_active_low(struct gpio_desc *desc)
+{
+	VALIDATE_DESC_VOID(desc);
+	change_bit(FLAG_ACTIVE_LOW, &desc->flags);
+}
+EXPORT_SYMBOL_GPL(gpiod_toggle_active_low);
+
 /* I/O calls are only valid after configuration completed; the relevant
  * "is this a valid GPIO" error checks should already have been done.
  *

include/linux/gpio/consumer.h

@@ -158,6 +158,7 @@ int gpiod_set_raw_array_value_cansleep(unsigned int array_size,
 
 int gpiod_set_debounce(struct gpio_desc *desc, unsigned debounce);
 int gpiod_set_transitory(struct gpio_desc *desc, bool transitory);
+void gpiod_toggle_active_low(struct gpio_desc *desc);
 
 int gpiod_is_active_low(const struct gpio_desc *desc);
 int gpiod_cansleep(const struct gpio_desc *desc);
@@ -483,6 +484,12 @@ static inline int gpiod_set_transitory(struct gpio_desc *desc, bool transitory)
 	return -ENOSYS;
 }
 
+static inline void gpiod_toggle_active_low(struct gpio_desc *desc)
+{
+	/* GPIO can never have been requested */
+	WARN_ON(desc);
+}
+
 static inline int gpiod_is_active_low(const struct gpio_desc *desc)
 {
 	/* GPIO can never have been requested */