USB: serial: pl2303: add support for tx xon/xoff flow control

Support hardware-level Xon/Xoff flow control in transmit direction with
pl2303.

I only know how to get the hardware to do IXON/!IXANY with ^S/^Q as control
characters, so I preserve the old behaviour for all other cases.

Signed-off-by: Florian Zumbiehl <florz@florz.de>
[ johan: rewrite logic using pl2303_termios_change() helper ]
Signed-off-by: Johan Hovold <johan@kernel.org>

diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c
index 46dd09da2434d8f1e8a1e0adb9fd82de099fdb5a..5d1a1931967e0e089ac4d6aafc135c1870138d6e 100644 (file)
--- a/drivers/usb/serial/pl2303.c
+++ b/drivers/usb/serial/pl2303.c
@@ -533,6 +533,17 @@ static int pl2303_set_line_request(struct usb_serial_port *port,
        return 0;
 }
 
+static bool pl2303_termios_change(const struct ktermios *a, const struct ktermios *b)
+{
+       bool ixon_change;
+
+       ixon_change = ((a->c_iflag ^ b->c_iflag) & (IXON | IXANY)) ||
+                       a->c_cc[VSTART] != b->c_cc[VSTART] ||
+                       a->c_cc[VSTOP] != b->c_cc[VSTOP];
+
+       return tty_termios_hw_change(a, b) || ixon_change;
+}
+
 static void pl2303_set_termios(struct tty_struct *tty,
                struct usb_serial_port *port, struct ktermios *old_termios)
 {
@@ -544,7 +555,7 @@ static void pl2303_set_termios(struct tty_struct *tty,
        int ret;
        u8 control;
 
-       if (old_termios && !tty_termios_hw_change(&tty->termios, old_termios))
+       if (old_termios && !pl2303_termios_change(&tty->termios, old_termios))
                return;
 
        buf = kzalloc(7, GFP_KERNEL);
@@ -662,6 +673,9 @@ static void pl2303_set_termios(struct tty_struct *tty,
                        pl2303_vendor_write(serial, 0x0, 0x41);
                else
                        pl2303_vendor_write(serial, 0x0, 0x61);
+       } else if (I_IXON(tty) && !I_IXANY(tty) && START_CHAR(tty) == 0x11 &&
+                       STOP_CHAR(tty) == 0x13) {
+               pl2303_vendor_write(serial, 0x0, 0xc0);
        } else {
                pl2303_vendor_write(serial, 0x0, 0x0);
        }