From: "Oleksiy Kebkal" <kebkal@gmail.com>

This patch leaves RTS alone when CRTSCTS is not set.

Current behaviour doesn't give any possibility to

1.  preconfigure port setting, because open operation implies RTS
   assertion and initial serial port setting may be wrong.

2.  realize peculiar serial flow control required by some hardware
   especially in embedded devices.

Signed-off-by: Oleksiy Kebkal <lesha@evologics.de>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/serial/serial_core.c |   42 ++++++++++++++++++++++-----------
 1 files changed, 28 insertions(+), 14 deletions(-)

diff -puN drivers/serial/serial_core.c~serial-suppress-rts-assertion-with-disabled-crtscts drivers/serial/serial_core.c
--- a/drivers/serial/serial_core.c~serial-suppress-rts-assertion-with-disabled-crtscts
+++ a/drivers/serial/serial_core.c
@@ -185,11 +185,15 @@ static int uart_startup(struct uart_stat
 			uart_change_speed(state, NULL);
 
 			/*
-			 * Setup the RTS and DTR signals once the
-			 * port is open and ready to respond.
+			 * Setup the RTS (in the case of hardware flow control)
+			 * and DTR signals once the port is open and ready to
+			 * respond.
 			 */
-			if (info->tty->termios->c_cflag & CBAUD)
-				uart_set_mctrl(port, TIOCM_RTS | TIOCM_DTR);
+			if (info->tty->termios->c_cflag & CBAUD) {
+				uart_set_mctrl(port, TIOCM_DTR);
+				if (info->flags & UIF_CTS_FLOW)
+					uart_set_mctrl(port, TIOCM_RTS);
+			}
 		}
 
 		if (info->flags & UIF_CTS_FLOW) {
@@ -230,10 +234,14 @@ static void uart_shutdown(struct uart_st
 		info->flags &= ~UIF_INITIALIZED;
 
 		/*
-		 * Turn off DTR and RTS early.
+		 * Turn off DTR and RTS (in the case of hardware flow control)
+		 * early.
 		 */
-		if (!info->tty || (info->tty->termios->c_cflag & HUPCL))
-			uart_clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);
+		if (!info->tty || (info->tty->termios->c_cflag & HUPCL)) {
+			uart_clear_mctrl(port, TIOCM_DTR);
+			if (info->flags & UIF_CTS_FLOW)
+				uart_clear_mctrl(port, TIOCM_RTS);
+               }
 
 		/*
 		 * clear delta_msr_wait queue to avoid mem leaks: we may free
@@ -1164,14 +1172,16 @@ static void uart_set_termios(struct tty_
 	uart_change_speed(state, old_termios);
 
 	/* Handle transition to B0 status */
-	if ((old_termios->c_cflag & CBAUD) && !(cflag & CBAUD))
-		uart_clear_mctrl(state->port, TIOCM_RTS | TIOCM_DTR);
+	if ((old_termios->c_cflag & CBAUD) && !(cflag & CBAUD)) {
+		uart_clear_mctrl(state->port, TIOCM_DTR);
+		if (state->info->flags & UIF_CTS_FLOW)
+			uart_clear_mctrl(state->port, TIOCM_RTS);
+       }
 
 	/* Handle transition away from B0 status */
 	if (!(old_termios->c_cflag & CBAUD) && (cflag & CBAUD)) {
 		unsigned int mask = TIOCM_DTR;
-		if (!(cflag & CRTSCTS) ||
-		    !test_bit(TTY_THROTTLED, &tty->flags))
+		if (!test_bit(TTY_THROTTLED, &tty->flags))
 			mask |= TIOCM_RTS;
 		uart_set_mctrl(state->port, mask);
 	}
@@ -1415,10 +1425,14 @@ static void uart_update_termios(struct u
 		uart_change_speed(state, NULL);
 
 		/*
-		 * And finally enable the RTS and DTR signals.
+		 * And finally enable the RTS (in the of case hardware flow
+		 * control) and DTR signals.
 		 */
-		if (tty->termios->c_cflag & CBAUD)
-			uart_set_mctrl(port, TIOCM_DTR | TIOCM_RTS);
+		if (tty->termios->c_cflag & CBAUD) {
+			uart_set_mctrl(port, TIOCM_DTR);
+			if (state->info->flags & UIF_CTS_FLOW)
+				uart_set_mctrl(port, TIOCM_RTS);
+		}
 	}
 }
 
_