USB: serial: ch341: fix modem-status handling

commit a0467a967f347842b30739aae636c44980265265 upstream.

The modem-status register was read as part of device configuration at
port_probe and then again at open (and reset-resume). During open (and
reset-resume) the MSR was read before submitting the interrupt URB,
something which could lead to an MSR-change going unnoticed when it
races with open (reset-resume).

Fix this by dropping the redundant reconfiguration of the port at every
open, and only read the MSR after the interrupt URB has been submitted.

Fixes: 664d5df92e88 ("USB: usb-serial ch341: support for DTR/RTS/CTS")
Signed-off-by: Johan Hovold <johan@kernel.org>
[bwh: Backported to 3.2:
 - Adjust context
 - Keep the 'serial' variable in ch341_open()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
index d50a6a6..57cb577 100644 (file)
--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -255,21 +255,11 @@ static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
        if (r < 0)
                goto out;
 
-       /* expect 0xff 0xee */
-       r = ch341_get_status(dev, priv);
-       if (r < 0)
-               goto out;
-
        r = ch341_set_baudrate_lcr(dev, priv, 0);
        if (r < 0)
                goto out;
 
        r = ch341_set_handshake(dev, priv->line_control);
-       if (r < 0)
-               goto out;
-
-       /* expect 0x9f 0xee */
-       r = ch341_get_status(dev, priv);
 
 out:   kfree(buffer);
        return r;
@@ -345,10 +335,6 @@ static int ch341_open(struct tty_struct *tty, struct usb_serial_port *port)
 
        dbg("ch341_open()");
 
-       r = ch341_configure(serial->dev, priv);
-       if (r)
-               return r;
-
        if (tty)
                ch341_set_termios(tty, port, NULL);
 
@@ -361,6 +347,12 @@ static int ch341_open(struct tty_struct *tty, struct usb_serial_port *port)
                return r;
        }
 
+       r = ch341_get_status(port->serial->dev, priv);
+       if (r < 0) {
+               dev_err(&port->dev, "failed to read modem status: %d\n", r);
+               goto err_kill_interrupt_urb;
+       }
+
        r = usb_serial_generic_open(tty, port);
        if (r)
                goto err_kill_interrupt_urb;
@@ -656,6 +648,12 @@ static int ch341_reset_resume(struct usb_interface *intf)
                                ret);
                        return ret;
                }
+
+               ret = ch341_get_status(port->serial->dev, priv);
+               if (ret < 0) {
+                       dev_err(&port->dev, "failed to read modem status: %d\n",
+                               ret);
+               }
        }
 
        return usb_serial_generic_resume(serial);