usb/serial/ch341: Add parity support

Based on wireshark packet traces from a windows machine.

ch340 and ch341 both seem to support all parity modes, but only the ch341
appears to support variable data bits and variable stop bits, so those are left
unimplemented, as before.

Tested on a generic usb-rs485 dongle with the chip label scratched off, and
some Modbus/RTU devices that required various parity settings.

Signed-off-by: Karl Palsson <karlp@tweak.net.au>

diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
index e98590aab633cd6491f2886842179d314ded5fe6..4f25aba5bdfcabe7304b18860be8527587390467 100644 (file)
--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -358,6 +358,7 @@ static void ch341_set_termios(struct tty_struct *tty,
        struct ch341_private *priv = usb_get_serial_port_data(port);
        unsigned baud_rate;
        unsigned long flags;
+       unsigned int par_flags;
 
        baud_rate = tty_get_baud_rate(tty);
 
@@ -368,10 +369,34 @@ static void ch341_set_termios(struct tty_struct *tty,
 
        /* Unimplemented:
         * (cflag & CSIZE) : data bits [5, 8]
-        * (cflag & PARENB) : parity {NONE, EVEN, ODD}
         * (cflag & CSTOPB) : stop bits [1, 2]
         */
 
+       /* CH340 doesn't appear to support variable stop bits or data bits */
+       if (C_PARENB(tty)) {
+               if (C_PARODD(tty)) {
+                       if (tty->termios.c_cflag & CMSPAR) {
+                               dev_dbg(&port->dev, "parity = mark\n");
+                               par_flags = 0xeb;
+                       } else {
+                               dev_dbg(&port->dev, "parity = odd\n");
+                               par_flags = 0xcb;
+                       }
+               } else {
+                       if (tty->termios.c_cflag & CMSPAR) {
+                               dev_dbg(&port->dev, "parity = space\n");
+                               par_flags = 0xfb;
+                       } else {
+                               dev_dbg(&port->dev, "parity = even\n");
+                               par_flags = 0xdb;
+                       }
+               }
+       } else {
+               dev_dbg(&port->dev, "parity = none\n");
+               par_flags = 0xc3;
+       }
+       ch341_control_out(port->serial->dev, 0x9a, 0x2518, par_flags);
+
        spin_lock_irqsave(&priv->lock, flags);
        if (C_BAUD(tty) == B0)
                priv->line_control &= ~(CH341_BIT_DTR | CH341_BIT_RTS);