SERIAL: core: add hardware assisted s/w flow control support

Ports which are capable of handling s/w flow control in hardware to
know when the s/w flow control termios settings are changed.  Add a
flag to allow the low level serial drivers to indicate that they
support this, and these changes should be propagated to them.

Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 14 insertions, 2 deletions

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index bc2065d323b9..bd10bbd56446 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1213,7 +1213,19 @@ static void uart_set_termios(struct tty_struct *tty,
         struct uart_port *uport = state->uart_port;
         unsigned long flags;
         unsigned int cflag = tty->termios.c_cflag;
+        unsigned int iflag_mask = IGNBRK|BRKINT|IGNPAR|PARMRK|INPCK;
+        bool sw_changed = false;
 
+        /*
+         * Drivers doing software flow control also need to know
+         * about changes to these input settings.
+         */
+        if (uport->flags & UPF_SOFT_FLOW) {
+                iflag_mask |= IXANY|IXON|IXOFF;
+                sw_changed =
+                   tty->termios.c_cc[VSTART] != old_termios->c_cc[VSTART] ||
+                   tty->termios.c_cc[VSTOP] != old_termios->c_cc[VSTOP];
+        }
 
         /*
          * These are the bits that are used to setup various
@@ -1221,11 +1233,11 @@ static void uart_set_termios(struct tty_struct *tty,
          * bits in c_cflag; c_[io]speed will always be set
          * appropriately by set_termios() in tty_ioctl.c
          */
-#define RELEVANT_IFLAG(iflag)   ((iflag) & (IGNBRK|BRKINT|IGNPAR|PARMRK|INPCK))
         if ((cflag ^ old_termios->c_cflag) == 0 &&
             tty->termios.c_ospeed == old_termios->c_ospeed &&
             tty->termios.c_ispeed == old_termios->c_ispeed &&
-            RELEVANT_IFLAG(tty->termios.c_iflag ^ old_termios->c_iflag) == 0) {
+            ((tty->termios.c_iflag ^ old_termios->c_iflag) & iflag_mask) == 0 &&
+            !sw_changed) {
                 return;
         }