gpiolib: provide gpiod_remove_hogs()

Currently all users of gpiod_add_hogs() call it only once at system
init so there never was any need for a mechanism allowing to remove
them. Now the upcoming gpio-sim will need to tear down chips with hogged
lines so provide a function that allows to remove hogs.

Signed-off-by: Bartosz Golaszewski <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Acked-by: Linus Walleij <[e-mail]>

drivers/gpio/gpiolib.c

···
 }
 EXPORT_SYMBOL_GPL(gpiod_add_hogs);
 
+void gpiod_remove_hogs(struct gpiod_hog *hogs)
+{
+	struct gpiod_hog *hog;
+
+	mutex_lock(&gpio_machine_hogs_mutex);
+	for (hog = &hogs[0]; hog->chip_label; hog++)
+		list_del(&hog->list);
+	mutex_unlock(&gpio_machine_hogs_mutex);
+}
+EXPORT_SYMBOL_GPL(gpiod_remove_hogs);
+
 static struct gpiod_lookup_table *gpiod_find_lookup_table(struct device *dev)
 {
 	const char *dev_id = dev ? dev_name(dev) : NULL;

include/linux/gpio/machine.h

···
 void gpiod_add_lookup_tables(struct gpiod_lookup_table **tables, size_t n);
 void gpiod_remove_lookup_table(struct gpiod_lookup_table *table);
 void gpiod_add_hogs(struct gpiod_hog *hogs);
+void gpiod_remove_hogs(struct gpiod_hog *hogs);
 #else /* ! CONFIG_GPIOLIB */
 static inline
 void gpiod_add_lookup_table(struct gpiod_lookup_table *table) {}
···
 static inline
 void gpiod_remove_lookup_table(struct gpiod_lookup_table *table) {}
 static inline void gpiod_add_hogs(struct gpiod_hog *hogs) {}
+static inline void gpiod_remove_hogs(struct gpiod_hog *hogs) {}
 #endif /* CONFIG_GPIOLIB */
 
 #endif /* __LINUX_GPIO_MACHINE_H */