From: Michal Schmidt <mschmidt@redhat.com>
Date: Tue, 4 Sep 2007 13:52:22 +0200
Subject: [misc] serial: assert DTR for serial console devices
Message-id: 46DD46F6.1060108@redhat.com
O-Subject: [RHEL5.2 PATCH] serial: assert DTR for serial console devices
Bugzilla: 244728

I originally submitted this patch for RHEL 5.1. The concensus was that
the fix was correct, but there were concerns about the theoretical
possibility of breaking previously working setups. It was proposed too
early after upstream inclusion and too late for 5.1.

Here it is again, this time for RHEL 5.2.

BZ: https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=244728

Description:
Current kernels do not assert DTR before printing to serial ports during
boot time. 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 the kernel doesn't actually open serial console ports. Known
affected devices are Sun's Dorado/Tucana and Gemini, and allegedly some
other non-Sun RS232 devices too.

Solution:
Assert DTR when the port is added. The patch is from Yinghai Lu
<Yinghai.Lu@Sun.COM>.

Upstream status:
The patch has been upstream since git commit 79492689... preceding Linux
v2.6.23-rc1.

Testing:
The patch was tested by Sun. It fixed the issue on Dorado/Tucana and
Gemini. It caused no problems on Galaxy 1/2/4 and Stinger.

Thanks,
Michal

Acked-by: Prarit Bhargava <prarit@redhat.com>
Acked-by: Chip Coldwell <coldwell@redhat.com>
Acked-by: Pete Zaitcev <zaitcev@redhat.com>
---
 drivers/serial/serial_core.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/serial/serial_core.c b/drivers/serial/serial_core.c
index c59dcb7..fef5991 100644
--- a/drivers/serial/serial_core.c
+++ b/drivers/serial/serial_core.c
@@ -1905,6 +1905,12 @@ uart_set_options(struct uart_port *port, struct console *co,
 	if (flow == 'r')
 		termios.c_cflag |= CRTSCTS;
 
+	/*
+	 * some uarts on other side don't support no flow control.
+	 * So we set * DTR in host uart to make them happy
+	 */
+	port->mctrl |= TIOCM_DTR;
+
 	port->ops->set_termios(port, &termios, NULL);
 	co->cflag = termios.c_cflag;
 
-- 
1.5.3.5.645.gbb47