USB: serial: belkin_sa: fix TIOCMBIS and TIOCMBIC

commit b6e0b30 upstream.

Asserting or deasserting a modem control line using TIOCMBIS or TIOCMBIC
should not deassert any lines that are not in the mask.

Fix this long-standing regression dating back to 2003 when the
tiocmset() callback was introduced.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: jhovold

drivers/usb/serial/belkin_sa.c

@@ -435,7 +435,7 @@ static int belkin_sa_tiocmset(struct tty_struct *tty,
 	struct belkin_sa_private *priv = usb_get_serial_port_data(port);
 	unsigned long control_state;
 	unsigned long flags;
-	int retval;
+	int retval = 0;
 	int rts = 0;
 	int dtr = 0;
 
@@ -452,26 +452,32 @@ static int belkin_sa_tiocmset(struct tty_struct *tty,
 	}
 	if (clear & TIOCM_RTS) {
 		control_state &= ~TIOCM_RTS;
-		rts = 0;
+		rts = 1;
 	}
 	if (clear & TIOCM_DTR) {
 		control_state &= ~TIOCM_DTR;
-		dtr = 0;
+		dtr = 1;
 	}
 
 	priv->control_state = control_state;
 	spin_unlock_irqrestore(&priv->lock, flags);
 
-	retval = BSA_USB_CMD(BELKIN_SA_SET_RTS_REQUEST, rts);
-	if (retval < 0) {
-		dev_err(&port->dev, "Set RTS error %d\n", retval);
-		goto exit;
+	if (rts) {
+		retval = BSA_USB_CMD(BELKIN_SA_SET_RTS_REQUEST,
+					!!(control_state & TIOCM_RTS));
+		if (retval < 0) {
+			dev_err(&port->dev, "Set RTS error %d\n", retval);
+			goto exit;
+		}
 	}
 
-	retval = BSA_USB_CMD(BELKIN_SA_SET_DTR_REQUEST, dtr);
-	if (retval < 0) {
-		dev_err(&port->dev, "Set DTR error %d\n", retval);
-		goto exit;
+	if (dtr) {
+		retval = BSA_USB_CMD(BELKIN_SA_SET_DTR_REQUEST,
+					!!(control_state & TIOCM_DTR));
+		if (retval < 0) {
+			dev_err(&port->dev, "Set DTR error %d\n", retval);
+			goto exit;
+		}
 	}
 exit:
 	return retval;