serial: core: Consider rs485 settings to drive RTS

Previously the rs485 settings weren't considered when setting the RTS
line, so e.g. closing and reopening a port made serial_core to drive
the line as if rs485 was disabled.

This patch fixes those issues.
Signed-off-by: Rafael Gago Castano <rgc@hms.se>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_core.c

@@ -165,6 +165,27 @@ uart_update_mctrl(struct uart_port *port, unsigned int set, unsigned int clear)
 #define uart_set_mctrl(port, set)	uart_update_mctrl(port, set, 0)
 #define uart_clear_mctrl(port, clear)	uart_update_mctrl(port, 0, clear)
 
+static void uart_port_dtr_rts(struct uart_port *uport, int raise)
+{
+	int rs485_on = uport->rs485_config &&
+		(uport->rs485.flags & SER_RS485_ENABLED);
+	int RTS_after_send = !!(uport->rs485.flags & SER_RS485_RTS_AFTER_SEND);
+
+	if (raise) {
+		if (rs485_on && !RTS_after_send) {
+			uart_set_mctrl(uport, TIOCM_DTR);
+			uart_clear_mctrl(uport, TIOCM_RTS);
+		} else {
+			uart_set_mctrl(uport, TIOCM_DTR | TIOCM_RTS);
+		}
+	} else {
+		unsigned int clear = TIOCM_DTR;
+
+		clear |= (!rs485_on || !RTS_after_send) ? TIOCM_RTS : 0;
+		uart_clear_mctrl(uport, clear);
+	}
+}
+
 /*
  * Startup the port.  This will be called once per open.  All calls
  * will be serialised by the per-port mutex.
@@ -214,7 +235,7 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
 		 * port is open and ready to respond.
 		 */
 		if (init_hw && C_BAUD(tty))
-			uart_set_mctrl(uport, TIOCM_RTS | TIOCM_DTR);
+			uart_port_dtr_rts(uport, 1);
 	}
 
 	/*
@@ -272,7 +293,7 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
 			uport->cons->cflag = tty->termios.c_cflag;
 
 		if (!tty || C_HUPCL(tty))
-			uart_clear_mctrl(uport, TIOCM_DTR | TIOCM_RTS);
+			uart_port_dtr_rts(uport, 0);
 
 		uart_port_shutdown(port);
 	}
@@ -1658,7 +1679,7 @@ static int uart_carrier_raised(struct tty_port *port)
 	return 0;
 }
 
-static void uart_dtr_rts(struct tty_port *port, int onoff)
+static void uart_dtr_rts(struct tty_port *port, int raise)
 {
 	struct uart_state *state = container_of(port, struct uart_state, port);
 	struct uart_port *uport;
@@ -1666,12 +1687,7 @@ static void uart_dtr_rts(struct tty_port *port, int onoff)
 	uport = uart_port_ref(state);
 	if (!uport)
 		return;
-
-	if (onoff)
-		uart_set_mctrl(uport, TIOCM_DTR | TIOCM_RTS);
-	else
-		uart_clear_mctrl(uport, TIOCM_DTR | TIOCM_RTS);
-
+	uart_port_dtr_rts(uport, raise);
 	uart_port_deref(uport);
 }