USB: serial: ch341: fix modem-control and B0 handling

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")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
index 6279df905c14cee7374a103d1ef9ac1ffc48fb63..0cc5056b304dbcff8e3460a5d634454b9c0959f7 100644 (file)
--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -384,10 +384,6 @@ static void ch341_set_termios(struct tty_struct *tty,
                ctrl |= CH341_LCR_STOP_BITS_2;
 
        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);
@@ -395,14 +391,16 @@ static void ch341_set_termios(struct tty_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);
 
+       ch341_set_handshake(port->serial->dev, priv->line_control);
 }
 
 static void ch341_break_ctl(struct tty_struct *tty, int break_state)