serial: keep the DTR setting for serial console.

with reverting "x86, serial: convert legacy COM ports to platform devices",
we will have the serial console before the port is probled again.

uart_add_one_port==>uart_configure_port==>set_mcttrl(port, 0) will clear
the DTR setting by uart_set_options().  then I will lose my output from
serial console again.

So try to keep DTR in uart_configure_port()

Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Andi Kleen <ak@suse.de>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/serial/serial_core.c b/drivers/serial/serial_core.c
index 3bb5d241dd40..0cf382b55d4b 100644
--- a/drivers/serial/serial_core.c
+++ b/drivers/serial/serial_core.c
@@ -2150,10 +2150,11 @@ uart_configure_port(struct uart_driver *drv, struct uart_state *state,
 
                 /*
                  * Ensure that the modem control lines are de-activated.
+                 * keep the DTR setting that is set in uart_set_options()
                  * We probably don't need a spinlock around this, but
                  */
                 spin_lock_irqsave(&port->lock, flags);
-                port->ops->set_mctrl(port, 0);
+                port->ops->set_mctrl(port, port->mctrl & TIOCM_DTR);
                 spin_unlock_irqrestore(&port->lock, flags);
 
                 /*