USB: cypress_m8: only wake up MSR queue on changes

Only wake up MSR wait queue on actual modem-status changes.
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/cypress_m8.c

@@ -1187,7 +1187,10 @@ static void cypress_read_int_callback(struct urb *urb)
 	if (priv->current_status != priv->prev_status) {
 		priv->diff_status |= priv->current_status ^
 			priv->prev_status;
-		wake_up_interruptible(&port->port.delta_msr_wait);
+
+		if (priv->diff_status & UART_MSR_MASK)
+			wake_up_interruptible(&port->port.delta_msr_wait);
+
 		priv->prev_status = priv->current_status;
 	}
 	spin_unlock_irqrestore(&priv->lock, flags);

drivers/usb/serial/cypress_m8.h

@@ -66,6 +66,7 @@
 #define CONTROL_RTS	0x10	/* request to send */
 #define CONTROL_RESET	0x08	/* sent with output report */
 
+#define UART_MSR_MASK	0xf0
 #define UART_RI		0x80	/* ring indicator */
 #define UART_CD		0x40	/* carrier detect */
 #define UART_DSR	0x20	/* data set ready */