commit 166b6eed405d08338af1cf2d8ea617a29e6edc83
Author: Simon Arlott <simon.arlott.org.uk>
Date:   Fri Nov 26 17:50:33 2010 +0000

    allow concurrent waiting to work

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 63ddb2f..397f8d5 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -1806,8 +1806,8 @@ static int ftdi_process_packet(struct tty_struct *tty,
 	status = packet[0] & FTDI_STATUS_B0_MASK;
 	if (status != priv->prev_status) {
 		priv->diff_status |= status ^ priv->prev_status;
-		wake_up_interruptible(&priv->delta_msr_wait);
 		priv->prev_status = status;
+		wake_up_interruptible_all(&priv->delta_msr_wait);
 	}
 
 	flag = TTY_NORMAL;
@@ -2141,6 +2141,7 @@ static int ftdi_ioctl(struct tty_struct *tty, struct file *file,
 {
 	struct usb_serial_port *port = tty->driver_data;
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
+	char status;
 
 	dbg("%s cmd 0x%04x", __func__, cmd);
 
@@ -2164,19 +2165,15 @@ static int ftdi_ioctl(struct tty_struct *tty, struct file *file,
 	 * This code is borrowed from linux/drivers/char/serial.c
 	 */
 	case TIOCMIWAIT:
+		if (priv != NULL)
+			status = priv->prev_status;
 		while (priv != NULL) {
 			interruptible_sleep_on(&priv->delta_msr_wait);
 			/* see if a signal did it */
 			if (signal_pending(current))
 				return -ERESTARTSYS;
 			else {
-				char diff = priv->diff_status;
-
-				if (diff == 0)
-					return -EIO; /* no change => error */
-
-				/* Consume all events */
-				priv->diff_status = 0;
+				char diff = status ^ priv->prev_status;
 
 				/* Return 0 if caller wanted to know about
 				   these bits */