serial: Introduce UPSTAT_SYNC_FIFO for synchronised FIFOs

This change adds a flag to indicate that a UART is has an external means
of synchronising its FIFO, without needing CTSRTS or XON/XOFF.

This allows us to use the throttle/unthrottle callbacks, without having
to claim other methods of flow control.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Tested-by: Eddie James <eajames@linux.vnet.ibm.com>
Tested-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 3 insertions, 2 deletions

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 0466f9f08a91..c47158c93202 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -674,8 +674,8 @@ static void uart_send_xchar(struct tty_struct *tty, char ch)
 static void uart_throttle(struct tty_struct *tty)
 {
         struct uart_state *state = tty->driver_data;
+        upstat_t mask = UPSTAT_SYNC_FIFO;
         struct uart_port *port;
-        upstat_t mask = 0;
 
         port = uart_port_ref(state);
         if (!port)
@@ -703,8 +703,8 @@ static void uart_throttle(struct tty_struct *tty)
 static void uart_unthrottle(struct tty_struct *tty)
 {
         struct uart_state *state = tty->driver_data;
+        upstat_t mask = UPSTAT_SYNC_FIFO;
         struct uart_port *port;
-        upstat_t mask = 0;
 
         port = uart_port_ref(state);
         if (!port)
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 1d356105f25a..d224961e1346 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -233,6 +233,7 @@ struct uart_port {
 #define UPSTAT_AUTORTS          ((__force upstat_t) (1 << 2))
 #define UPSTAT_AUTOCTS          ((__force upstat_t) (1 << 3))
 #define UPSTAT_AUTOXOFF         ((__force upstat_t) (1 << 4))
+#define UPSTAT_SYNC_FIFO        ((__force upstat_t) (1 << 5))
 
         int                     hw_stopped;             /* sw-assisted CTS flow state */
         unsigned int            mctrl;                  /* current modem ctrl settings */