tty_port: register tty ports with serdev bus

Register a serdev controller with the serdev bus when a tty_port is
registered. This creates the serdev controller and create's serdev
devices for any DT child nodes of the tty_port's parent (i.e. the UART
device).
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-By: Sebastian Reichel <sre@kernel.org>
Tested-By: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_port.c

@@ -16,6 +16,7 @@
 #include <linux/bitops.h>
 #include <linux/delay.h>
 #include <linux/module.h>
+#include <linux/serdev.h>
 
 static int tty_port_default_receive_buf(struct tty_port *port,
 					const unsigned char *p,
@@ -128,7 +129,15 @@ struct device *tty_port_register_device_attr(struct tty_port *port,
 		struct device *device, void *drvdata,
 		const struct attribute_group **attr_grp)
 {
+	struct device *dev;
+
 	tty_port_link_device(port, driver, index);
+
+	dev = serdev_tty_port_register(port, device, driver, index);
+	if (PTR_ERR(dev) != -ENODEV)
+		/* Skip creating cdev if we registered a serdev device */
+		return dev;
+
 	return tty_register_device_attr(driver, index, device, drvdata,
 			attr_grp);
 }
@@ -180,6 +189,9 @@ static void tty_port_destructor(struct kref *kref)
 	/* check if last port ref was dropped before tty release */
 	if (WARN_ON(port->itty))
 		return;
+
+	serdev_tty_port_unregister(port);
+
 	if (port->xmit_buf)
 		free_page((unsigned long)port->xmit_buf);
 	tty_port_destroy(port);