From: Yinghai Lu <Yinghai.Lu@Sun.COM>

Some RS-232 devices require DTR to be asserted before they can be used.  DTR
is normally asserted in uart_startup() when the port is opened.  But we don't
actually open serial console ports, so assert DTR when the port is added.

BTW:
earlyprintk and early_uart are hard coded to set DTR/RTS.

Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Andi Kleen <ak@suse.de>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Gerd Hoffmann <kraxel@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/serial/serial_core.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletion(-)

diff -puN drivers/serial/serial_core.c~serial-assert-dtr-for-serial-console-devices drivers/serial/serial_core.c
--- a/drivers/serial/serial_core.c~serial-assert-dtr-for-serial-console-devices
+++ a/drivers/serial/serial_core.c
@@ -2303,8 +2303,14 @@ int uart_add_one_port(struct uart_driver
 	 * It may be that the port was not available.
 	 */
 	if (port->type != PORT_UNKNOWN &&
-	    port->cons && !(port->cons->flags & CON_ENABLED))
+	    port->cons && !(port->cons->flags & CON_ENABLED)) {
+		/*
+		 * We normally assert DTR when a port is opened, but serial
+		 * console devices aren't actually opened, so do it here.
+		 */
+		uart_set_mctrl(port, TIOCM_DTR);
 		register_console(port->cons);
+	}
 
 	/*
 	 * Ensure UPF_DEAD is not set.
_