TTY: add tty_port_link_device

This is for those drivers which do not have dynamic device creation
(do not call tty_port_register_device) and do not want to implement
tty->ops->install (will not call tty_port_install). They still have to
provide the link somehow though.

And this newly added function is exactly to serve that purpose.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_port.c

@@ -33,6 +33,26 @@ void tty_port_init(struct tty_port *port)
 }
 EXPORT_SYMBOL(tty_port_init);
 
+/**
+ * tty_port_link_device - link tty and tty_port
+ * @port: tty_port of the device
+ * @driver: tty_driver for this device
+ * @index: index of the tty
+ *
+ * Provide the tty layer wit ha link from a tty (specified by @index) to a
+ * tty_port (@port). Use this only if neither tty_port_register_device nor
+ * tty_port_install is used in the driver. If used, this has to be called before
+ * tty_register_driver.
+ */
+void tty_port_link_device(struct tty_port *port,
+		struct tty_driver *driver, unsigned index)
+{
+	if (WARN_ON(index >= driver->num))
+		return;
+	driver->ports[index] = port;
+}
+EXPORT_SYMBOL_GPL(tty_port_link_device);
+
 /**
  * tty_port_register_device - register tty device
  * @port: tty_port of the device
@@ -48,7 +68,7 @@ struct device *tty_port_register_device(struct tty_port *port,
 		struct tty_driver *driver, unsigned index,
 		struct device *device)
 {
-	driver->ports[index] = port;
+	tty_port_link_device(port, driver, index);
 	return tty_register_device(driver, index, device);
 }
 EXPORT_SYMBOL_GPL(tty_port_register_device);

include/linux/tty.h

@@ -497,6 +497,8 @@ extern int tty_write_lock(struct tty_struct *tty, int ndelay);
 #define tty_is_writelocked(tty)  (mutex_is_locked(&tty->atomic_write_lock))
 
 extern void tty_port_init(struct tty_port *port);
+extern void tty_port_link_device(struct tty_port *port,
+		struct tty_driver *driver, unsigned index);
 extern struct device *tty_port_register_device(struct tty_port *port,
 		struct tty_driver *driver, unsigned index,
 		struct device *device);