USB: serial: call handle_dcd_change in ftdi driver.

When the device receive a DCD status change, forward the signal to the
USB serial system. This way, we can detect, for instance, PPS pulses.

Signed-off-by: Paul Chavent <paul.chavent@onera.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/ftdi_sio.c

@@ -1966,8 +1966,16 @@ static int ftdi_process_packet(struct usb_serial_port *port,
 			port->icount.dsr++;
 		if (diff_status & FTDI_RS0_RI)
 			port->icount.rng++;
-		if (diff_status & FTDI_RS0_RLSD)
+		if (diff_status & FTDI_RS0_RLSD) {
+			struct tty_struct *tty;
+
 			port->icount.dcd++;
+			tty = tty_port_tty_get(&port->port);
+			if (tty)
+				usb_serial_handle_dcd_change(port, tty,
+						status & FTDI_RS0_RLSD);
+			tty_kref_put(tty);
+		}
 
 		wake_up_interruptible(&port->port.delta_msr_wait);
 		priv->prev_status = status;