gpio: add SRCU infrastructure to struct gpio_desc

Extend the GPIO descriptor with an SRCU structure in order to serialize
the access to the label. 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

@@ -672,6 +672,10 @@ EXPORT_SYMBOL_GPL(gpiochip_line_is_valid);
 static void gpiodev_release(struct device *dev)
 {
 	struct gpio_device *gdev = to_gpio_device(dev);
+	unsigned int i;
+
+	for (i = 0; i < gdev->ngpio; i++)
+		cleanup_srcu_struct(&gdev->descs[i].srcu);
 
 	ida_free(&gpio_ida, gdev->id);
 	kfree_const(gdev->label);
@@ -836,7 +840,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 			       struct lock_class_key *request_key)
 {
 	struct gpio_device *gdev;
-	unsigned int i;
+	unsigned int i, j;
 	int base = 0;
 	int ret = 0;
 
@@ -970,6 +974,13 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	for (i = 0; i < gc->ngpio; i++) {
 		struct gpio_desc *desc = &gdev->descs[i];
 
+		ret = init_srcu_struct(&desc->srcu);
+		if (ret) {
+			for (j = 0; j < i; j++)
+				cleanup_srcu_struct(&gdev->descs[j].srcu);
+			goto err_remove_of_chip;
+		}
+
 		if (gc->get_direction && gpiochip_line_is_valid(gc, i)) {
 			assign_bit(FLAG_IS_OUT,
 				   &desc->flags, !gc->get_direction(gc, i));
@@ -981,7 +992,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 
 	ret = gpiochip_add_pin_ranges(gc);
 	if (ret)
-		goto err_remove_of_chip;
+		goto err_cleanup_desc_srcu;
 
 	acpi_gpiochip_add(gc);
 
@@ -1020,6 +1031,9 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	gpiochip_irqchip_free_valid_mask(gc);
 err_remove_acpi_chip:
 	acpi_gpiochip_remove(gc);
+err_cleanup_desc_srcu:
+	for (i = 0; i < gdev->ngpio; i++)
+		cleanup_srcu_struct(&gdev->descs[i].srcu);
 err_remove_of_chip:
 	gpiochip_free_hogs(gc);
 	of_gpiochip_remove(gc);

drivers/gpio/gpiolib.h

@@ -17,6 +17,7 @@
 #include <linux/module.h>
 #include <linux/notifier.h>
 #include <linux/rwsem.h>
+#include <linux/srcu.h>
 
 #define GPIOCHIP_NAME	"gpiochip"
 
@@ -147,6 +148,7 @@ void gpiod_line_state_notify(struct gpio_desc *desc, unsigned long action);
  * @label:		Name of the consumer
  * @name:		Line name
  * @hog:		Pointer to the device node that hogs this line (if any)
+ * @srcu:		SRCU struct protecting the label pointer.
  *
  * These are obtained using gpiod_get() and are preferable to the old
  * integer-based handles.
@@ -184,6 +186,7 @@ struct gpio_desc {
 #ifdef CONFIG_OF_DYNAMIC
 	struct device_node	*hog;
 #endif
+	struct srcu_struct	srcu;
 };
 
 #define gpiod_not_found(desc)		(IS_ERR(desc) && PTR_ERR(desc) == -ENOENT)