USB: serial: ch341: fix lost character on LCR updates

commit 8e83622ae7ca481c76c8fd9579877f6abae64ca2 upstream.

Disable LCR updates for pre-0x30 devices which use a different (unknown)
protocol for line control and where the current register write causes
the next received character to be lost.

Note that updating LCR using the INIT command has no effect on these
devices either.

Reported-by: Jonathan Woithe <jwoithe@just42.net>
Tested-by: Jonathan Woithe <jwoithe@just42.net>
Link: https://lore.kernel.org/r/Ys1iPTfiZRWj2gXs@marvin.atrad.com.au
Fixes: 4e46c410e050 ("USB: serial: ch341: reinitialize chip on reconfiguration")
Fixes: 55fa15b5987d ("USB: serial: ch341: fix baud rate and line-control handling")
Cc: stable@vger.kernel.org      # 4.10
Signed-off-by: Johan Hovold <johan@kernel.org>
[ johan: adjust context to 4.19 ]
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
index 1f6761a4daafd3ef157e75ed491265f728b2dc89..db39b6a6d2478ac24cfca1ce36023de2800ac5b7 100644 (file)
--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -99,6 +99,8 @@ struct ch341_private {
        u8 mcr;
        u8 msr;
        u8 lcr;
+
+       u8 version;
 };
 
 static void ch341_set_termios(struct tty_struct *tty,
@@ -184,6 +186,9 @@ static int ch341_set_baudrate_lcr(struct usb_device *dev,
        if (r)
                return r;
 
+       if (priv->version < 0x30)
+               return 0;
+
        r = ch341_control_out(dev, CH341_REQ_WRITE_REG, 0x2518, lcr);
        if (r)
                return r;
@@ -235,7 +240,9 @@ static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
        r = ch341_control_in(dev, CH341_REQ_READ_VERSION, 0, 0, buffer, size);
        if (r < 0)
                goto out;
-       dev_dbg(&dev->dev, "Chip version: 0x%02x\n", buffer[0]);
+
+       priv->version = buffer[0];
+       dev_dbg(&dev->dev, "Chip version: 0x%02x\n", priv->version);
 
        r = ch341_control_out(dev, CH341_REQ_SERIAL_INIT, 0, 0);
        if (r < 0)