[PATCH 5/5] serial: assert DTR for serial console devices

[Yinghai Lu]

[PATCH 5/5] 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.

Signed-off-by: Yinghai Lu <yinghai.lu@xxxxxxx>
Cc: Russell King <rmk@xxxxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxx>
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@xxxxxx>

diff --git a/drivers/serial/serial_core.c b/drivers/serial/serial_core.c
index 326020f..e5a3d8b 100644
--- a/drivers/serial/serial_core.c
+++ b/drivers/serial/serial_core.c
@@ -2303,8 +2303,14 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *port)
 	 * 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.
-
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