serdev: add of_ helper to get serdev controller

add of_find_serdev_controller_by_node to obtain a
serdev_controller from the device_node, which
can help if the serdev_device is not described
over device tree and instantiation of the device
happens from a different driver, for the same purpose
an option to not delete an empty serdev controller
is added.

Signed-off-by: Vaishnav M A <vaishnav@beagleboard.org>

drivers/tty/serdev/core.c

@@ -582,6 +582,17 @@ static int of_serdev_register_devices(struct serdev_controller *ctrl)
 	return 0;
 }
 
+struct serdev_controller *of_find_serdev_controller_by_node(struct device_node *node)
+{
+	struct device *dev = bus_find_device_by_of_node(&serdev_bus_type, node);
+
+	if (!dev)
+		return NULL;
+
+	return (dev->type == &serdev_ctrl_type) ? to_serdev_controller(dev) : NULL;
+}
+EXPORT_SYMBOL_GPL(of_find_serdev_controller_by_node);
+
 #ifdef CONFIG_ACPI
 
 #define SERDEV_ACPI_MAX_SCAN_DEPTH 32
@@ -779,6 +790,12 @@ int serdev_controller_add(struct serdev_controller *ctrl)
 
 	pm_runtime_enable(&ctrl->dev);
 
+	/* provide option to not delete a serdev controller without devices
+	 * if property is present
+	 */
+	if (device_property_present(&ctrl->dev, "force-empty-serdev-controller"))
+		return 0;
+
 	ret_of = of_serdev_register_devices(ctrl);
 	ret_acpi = acpi_serdev_register_devices(ctrl);
 	if (ret_of && ret_acpi) {

include/linux/serdev.h

@@ -115,6 +115,8 @@ static inline struct serdev_controller *to_serdev_controller(struct device *d)
 	return container_of(d, struct serdev_controller, dev);
 }
 
+struct serdev_controller *of_find_serdev_controller_by_node(struct device_node *node);
+
 static inline void *serdev_device_get_drvdata(const struct serdev_device *serdev)
 {
 	return dev_get_drvdata(&serdev->dev);