gpio: add SRCU infrastructure to struct gpio_device

Add the SRCU struct to GPIO device. It will be used to serialize access
to the GPIO chip pointer. Initialize and clean it up where applicable.
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/gpio/gpiolib.c

@@ -680,6 +680,7 @@ static void gpiodev_release(struct device *dev)
 	ida_free(&gpio_ida, gdev->id);
 	kfree_const(gdev->label);
 	kfree(gdev->descs);
+	cleanup_srcu_struct(&gdev->srcu);
 	kfree(gdev);
 }
 
@@ -948,6 +949,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	BLOCKING_INIT_NOTIFIER_HEAD(&gdev->device_notifier);
 	init_rwsem(&gdev->sem);
 
+	ret = init_srcu_struct(&gdev->srcu);
+	if (ret)
+		goto err_remove_from_list;
+
 #ifdef CONFIG_PINCTRL
 	INIT_LIST_HEAD(&gdev->pin_ranges);
 #endif
@@ -955,15 +960,15 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	if (gc->names) {
 		ret = gpiochip_set_desc_names(gc);
 		if (ret)
-			goto err_remove_from_list;
+			goto err_cleanup_gdev_srcu;
 	}
 	ret = gpiochip_set_names(gc);
 	if (ret)
-		goto err_remove_from_list;
+		goto err_cleanup_gdev_srcu;
 
 	ret = gpiochip_init_valid_mask(gc);
 	if (ret)
-		goto err_remove_from_list;
+		goto err_cleanup_gdev_srcu;
 
 	ret = of_gpiochip_add(gc);
 	if (ret)
@@ -1038,6 +1043,8 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 err_free_gpiochip_mask:
 	gpiochip_remove_pin_ranges(gc);
 	gpiochip_free_valid_mask(gc);
+err_cleanup_gdev_srcu:
+	cleanup_srcu_struct(&gdev->srcu);
 err_remove_from_list:
 	scoped_guard(mutex, &gpio_devices_lock)
 		list_del_rcu(&gdev->list);

drivers/gpio/gpiolib.h

@@ -49,6 +49,7 @@
  * @sem: protects the structure from a NULL-pointer dereference of @chip by
  *       user-space operations when the device gets unregistered during
  *       a hot-unplug event
+ * @srcu: protects the pointer to the underlying GPIO chip
  * @pin_ranges: range of pins served by the GPIO driver
  *
  * This state container holds most of the runtime variable data
@@ -73,6 +74,7 @@ struct gpio_device {
 	struct blocking_notifier_head line_state_notifier;
 	struct blocking_notifier_head device_notifier;
 	struct rw_semaphore	sem;
+	struct srcu_struct	srcu;
 
 #ifdef CONFIG_PINCTRL
 	/*