USB: ch341 serial: fix port number changed after resume

This patch fixes the following bug:
	.plug ch341 usb serial port into a hub port;
	.ch341 driver bound to the device and /dev/ttyUSB0 comes
	.open /dev/ttyUSB0 by minicom and we can use the serial successfully
	.suspend the ch341 usb serial device(such as: echo suspend > power/level)
	.resume the ch341 usb serial device (such as: echo on > power/level)
	.new port /dev/ttyUSB1 comes ,and the original /dev/ttyUSB0 still exists,
but is no longer usable by minicom

The patch adds suspend and resume callback to ch341 usb driver to prevent it
from unbinding during suspend. The /dev/ttyUSB0 is not released until being
closed, so /dev/ttyUSB1 comes after resume, and the original /dev/ttyUSB0 is
no longer usable by minicom. It is really a mess for a minicom user.

This patch also adds the reset_resume callback to make it usable after resuming
from STR or hibernation, for generally STR or hibernation will make the vbus
of root-hub lost.

Finally enable the driver's supports_autosuspend, for the device is in working
order with it.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/ch341.c

@@ -529,12 +529,34 @@ static int ch341_tiocmget(struct tty_struct *tty, struct file *file)
 	return result;
 }
 
+
+static int ch341_reset_resume(struct usb_interface *intf)
+{
+	struct usb_device *dev = interface_to_usbdev(intf);
+	struct usb_serial *serial = NULL;
+	struct ch341_private *priv;
+
+	serial = usb_get_intfdata(intf);
+	priv = usb_get_serial_port_data(serial->port[0]);
+
+	/*reconfigure ch341 serial port after bus-reset*/
+	ch341_configure(dev, priv);
+
+	usb_serial_resume(intf);
+
+	return 0;
+}
+
 static struct usb_driver ch341_driver = {
 	.name		= "ch341",
 	.probe		= usb_serial_probe,
 	.disconnect	= usb_serial_disconnect,
+	.suspend	= usb_serial_suspend,
+	.resume		= usb_serial_resume,
+	.reset_resume	= ch341_reset_resume,
 	.id_table	= id_table,
 	.no_dynamic_id	= 1,
+	.supports_autosuspend =	1,
 };
 
 static struct usb_serial_driver ch341_device = {