1 files changed, 16 insertions, 25 deletions

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 9699580331a..8fe034d2d3e 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -2328,6 +2328,8 @@ static int ftdi_ioctl(struct tty_struct *tty,
 {
         struct usb_serial_port *port = tty->driver_data;
         struct ftdi_private *priv = usb_get_serial_port_data(port);
+        struct async_icount cnow;
+        struct async_icount cprev;
 
         dbg("%s cmd 0x%04x", __func__, cmd);
 
@@ -2347,41 +2349,30 @@ static int ftdi_ioctl(struct tty_struct *tty,
          * - mask passed in arg for lines of interest
          *   (use |'ed TIOCM_RNG/DSR/CD/CTS for masking)
          * Caller should use TIOCGICOUNT to see which one it was.
-         * (except that the driver doesn't support it !)
          *
          * This code is borrowed from linux/drivers/char/serial.c
          */
         case TIOCMIWAIT:
-                while (priv != NULL) {
+                cprev = priv->icount;
+                while (1) {
                         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;
-
-                                /* Return 0 if caller wanted to know about
-                                   these bits */
-                                if (((arg & TIOCM_RNG) && (diff & FTDI_RS0_RI)) ||
-                                    ((arg & TIOCM_DSR) && (diff & FTDI_RS0_DSR)) ||
-                                    ((arg & TIOCM_CD)  && (diff & FTDI_RS0_RLSD)) ||
-                                    ((arg & TIOCM_CTS) && (diff & FTDI_RS0_CTS))) {
-                                        return 0;
-                                }
-                                /*
-                                 * Otherwise caller can't care less about what
-                                 * happened,and so we continue to wait for more
-                                 * events.
-                                 */
+                        cnow = priv->icount;
+                        if (cnow.rng == cprev.rng && cnow.dsr == cprev.dsr &&
+                            cnow.dcd == cprev.dcd && cnow.cts == cprev.cts)
+                                return -EIO; /* no change => error */
+                        if (((arg & TIOCM_RNG) && (cnow.rng != cprev.rng)) ||
+                            ((arg & TIOCM_DSR) && (cnow.dsr != cprev.dsr)) ||
+                            ((arg & TIOCM_CD)  && (cnow.dcd != cprev.dcd)) ||
+                            ((arg & TIOCM_CTS) && (cnow.cts != cprev.cts))) {
+                                return 0;
                         }
+                        cprev = cnow;
                 }
-                return 0;
+                /* not reached */
+                break;
         case TIOCSERGETLSR:
                 return get_lsr_info(port, (struct serial_struct __user *)arg);
                 break;