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

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@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 9 insertions, 9 deletions

diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
index 22b2c464b468..e98590aab633 100644
--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -362,24 +362,24 @@ static void ch341_set_termios(struct tty_struct *tty,
         baud_rate = tty_get_baud_rate(tty);
 
         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;
                 ch341_set_baudrate(port->serial->dev, priv);
-        } 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);
-
         /* Unimplemented:
          * (cflag & CSIZE) : data bits [5, 8]
          * (cflag & PARENB) : parity {NONE, EVEN, ODD}
          * (cflag & CSTOPB) : stop bits [1, 2]
          */
+
+        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)