serial: assert DTR for serial console devices
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.
rmk says
The only issue I can think of is the possibility for an attached modem to
auto-answer or maybe even auto-dial before the system is ready for it to do
so. Might have an undesirable cost implication for some running with such a
setup.
Apart from that, I can't think of any other side effect of this specific
patch.
Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>
Acked-by: 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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/serial/serial_core.c b/drivers/serial/serial_core.c
index 326020f..9c57486 100644
--- a/drivers/serial/serial_core.c
+++ b/drivers/serial/serial_core.c
@@ -1910,6 +1910,12 @@
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;