[PATCH 1/5] serial: Introduce UPSTAT_SYNC_FIFO for synchronised FIFOs

[Jeremy Kerr <jk@ozlabs.org>]

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>
---
 drivers/tty/serial/serial_core.c | 4 ++--
 include/linux/serial_core.h      | 1 +
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index f534a40aebde..8f3dfc8b5307 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -678,7 +678,7 @@ static void uart_throttle(struct tty_struct *tty)
 	if (C_CRTSCTS(tty))
 		mask |= UPSTAT_AUTORTS;
 
-	if (port->status & mask) {
+	if (port->status & (mask | UPSTAT_SYNC_FIFO)) {
 		port->ops->throttle(port);
 		mask &= ~port->status;
 	}
@@ -707,7 +707,7 @@ static void uart_unthrottle(struct tty_struct *tty)
 	if (C_CRTSCTS(tty))
 		mask |= UPSTAT_AUTORTS;
 
-	if (port->status & mask) {
+	if (port->status & (mask | UPSTAT_SYNC_FIFO)) {
 		port->ops->unthrottle(port);
 		mask &= ~port->status;
 	}
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 1775500294bb..bf600ae0290d 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -232,6 +232,7 @@ 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 */
-- 
2.14.1