[PATCH 3.16 201/370] USB: serial: ch341: fix modem-control and B0 handling

[Ben Hutchings]

3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Johan Hovold <johan@xxxxxxxxxx>

commit 030ee7ae52a46a2be52ccc8242c4a330aba8d38e upstream.

The modem-control signals are managed by the tty-layer during open and
should not be asserted prematurely when set_termios is called from
driver open.

Also make sure that the signals are asserted only when changing speed
from B0.

Fixes: 664d5df92e88 ("USB: usb-serial ch341: support for DTR/RTS/CTS")
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/usb/serial/ch341.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -357,10 +357,6 @@ static void ch341_set_termios(struct tty
 	ctrl = CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX | CH341_LCR_CS8;
 
 	if (baud_rate) {
-		spin_lock_irqsave(&priv->lock, flags);
-		priv->line_control |= (CH341_BIT_DTR | CH341_BIT_RTS);
-		spin_unlock_irqrestore(&priv->lock, flags);
-
 		priv->baud_rate = baud_rate;
 
 		r = ch341_init_set_baudrate(port->serial->dev, priv, ctrl);
@@ -368,13 +364,14 @@ static void ch341_set_termios(struct tty
 			priv->baud_rate = tty_termios_baud_rate(old_termios);
 			tty_termios_copy_hw(&tty->termios, old_termios);
 		}
-	} else {
-		spin_lock_irqsave(&priv->lock, flags);
-		priv->line_control &= ~(CH341_BIT_DTR | CH341_BIT_RTS);
-		spin_unlock_irqrestore(&priv->lock, flags);
 	}
 
-	ch341_set_handshake(port->serial->dev, priv->line_control);
+	spin_lock_irqsave(&priv->lock, flags);
+	if (C_BAUD(tty) == B0)
+		priv->line_control &= ~(CH341_BIT_DTR | CH341_BIT_RTS);
+	else if (old_termios && (old_termios->c_cflag & CBAUD) == B0)
+		priv->line_control |= (CH341_BIT_DTR | CH341_BIT_RTS);
+	spin_unlock_irqrestore(&priv->lock, flags);
 
 	/* Unimplemented:
 	 * (cflag & CSIZE) : data bits [5, 8]