gpio: remove const modifier from gpiod_get_direction()

Although gpiod_get_direction() can be considered side-effect free for
consumers, its internals involve setting or clearing bits in the
affected GPIO descriptor, for which we need to force-cast the const
descriptor variable to non-const. This could lead to incorrect behavior
if the compiler decides to optimize here, so remove this const
attribute. The intent is to make gpiod_get_direction() private anyway,
so it does not really matter.
Reported-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib-sysfs.c

@@ -41,7 +41,7 @@ static DEFINE_MUTEX(sysfs_lock);
 static ssize_t gpio_direction_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
-	const struct gpio_desc	*desc = dev_get_drvdata(dev);
+	struct gpio_desc	*desc = dev_get_drvdata(dev);
 	ssize_t			status;
 
 	mutex_lock(&sysfs_lock);

drivers/gpio/gpiolib.c

@@ -148,7 +148,7 @@ static int gpiochip_find_base(int ngpio)
  *
  * This function may sleep if gpiod_cansleep() is true.
  */
-int gpiod_get_direction(const struct gpio_desc *desc)
+int gpiod_get_direction(struct gpio_desc *desc)
 {
 	struct gpio_chip	*chip;
 	unsigned		offset;
@@ -164,13 +164,11 @@ int gpiod_get_direction(const struct gpio_desc *desc)
 	if (status > 0) {
 		/* GPIOF_DIR_IN, or other positive */
 		status = 1;
-		/* FLAG_IS_OUT is just a cache of the result of get_direction(),
-		 * so it does not affect constness per se */
-		clear_bit(FLAG_IS_OUT, &((struct gpio_desc *)desc)->flags);
+		clear_bit(FLAG_IS_OUT, &desc->flags);
 	}
 	if (status == 0) {
 		/* GPIOF_DIR_OUT */
-		set_bit(FLAG_IS_OUT, &((struct gpio_desc *)desc)->flags);
+		set_bit(FLAG_IS_OUT, &desc->flags);
 	}
 	return status;
 }

include/linux/gpio/consumer.h

@@ -66,7 +66,7 @@ __devm_gpiod_get_index_optional(struct device *dev, const char *con_id,
 			      unsigned int index, enum gpiod_flags flags);
 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc);
 
-int gpiod_get_direction(const struct gpio_desc *desc);
+int gpiod_get_direction(struct gpio_desc *desc);
 int gpiod_direction_input(struct gpio_desc *desc);
 int gpiod_direction_output(struct gpio_desc *desc, int value);
 int gpiod_direction_output_raw(struct gpio_desc *desc, int value);