1 files changed, 25 insertions, 9 deletions

diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c
index 1e3318dfa1cb..beb8edce4ef2 100644
--- a/drivers/usb/serial/pl2303.c
+++ b/drivers/usb/serial/pl2303.c
@@ -142,6 +142,8 @@ struct pl2303_private {
 	spinlock_t lock;
 	u8 line_control;
 	u8 line_status;
+
+	u8 line_settings[7];
 };
 
 static int pl2303_vendor_read(__u16 value, __u16 index,
@@ -339,11 +341,6 @@ static void pl2303_set_termios(struct tty_struct *tty,
 	int i;
 	u8 control;
 
-	/*
-	 * The PL2303 is reported to lose bytes if you change serial settings
-	 * even to the same values as before. Thus we actually need to filter
-	 * in this specific case.
-	 */
 	if (old_termios && !tty_termios_hw_change(&tty->termios, old_termios))
 		return;
 
@@ -428,10 +425,29 @@ static void pl2303_set_termios(struct tty_struct *tty,
 		dev_dbg(&port->dev, "parity = none\n");
 	}
 
-	i = usb_control_msg(serial->dev, usb_sndctrlpipe(serial->dev, 0),
-			    SET_LINE_REQUEST, SET_LINE_REQUEST_TYPE,
-			    0, 0, buf, 7, 100);
-	dev_dbg(&port->dev, "0x21:0x20:0:0  %d\n", i);
+	/*
+	 * Some PL2303 are known to lose bytes if you change serial settings
+	 * even to the same values as before. Thus we actually need to filter
+	 * in this specific case.
+	 *
+	 * Note that the tty_termios_hw_change check above is not sufficient
+	 * as a previously requested baud rate may differ from the one
+	 * actually used (and stored in old_termios).
+	 *
+	 * NOTE: No additional locking needed for line_settings as it is
+	 *       only used in set_termios, which is serialised against itself.
+	 */
+	if (!old_termios || memcmp(buf, priv->line_settings, 7)) {
+		i = usb_control_msg(serial->dev,
+				    usb_sndctrlpipe(serial->dev, 0),
+				    SET_LINE_REQUEST, SET_LINE_REQUEST_TYPE,
+				    0, 0, buf, 7, 100);
+
+		dev_dbg(&port->dev, "0x21:0x20:0:0  %d\n", i);
+
+		if (i == 7)
+			memcpy(priv->line_settings, buf, 7);
+	}
 
 	/* change control lines if we are switching to or from B0 */
 	spin_lock_irqsave(&priv->lock, flags);