serial: avoid waking up closed serial ports on resume

When we boot, serial ports remain in low power mode until they're used either
by userspace or for the kernel console.

However, if you suspend the system, and then resume, all serial ports will be
taken out of low power mode.  This is bad news for embedded devices where this
can mean higher power consumption.

Only bring a serial port out of low power mode if the port is being used as
the kernel console, or is in use by userspace.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/serial/serial_core.c

@@ -2029,8 +2029,6 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *port)
 	}
 	port->suspended = 0;
 
-	uart_change_pm(state, 0);
-
 	/*
 	 * Re-enable the console device after suspending.
 	 */
@@ -2049,6 +2047,7 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *port)
 		if (state->info && state->info->tty && termios.c_cflag == 0)
 			termios = *state->info->tty->termios;
 
+		uart_change_pm(state, 0);
 		port->ops->set_termios(port, &termios, NULL);
 		console_start(port->cons);
 	}
@@ -2057,6 +2056,7 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *port)
 		const struct uart_ops *ops = port->ops;
 		int ret;
 
+		uart_change_pm(state, 0);
 		ops->set_mctrl(port, 0);
 		ret = ops->startup(port);
 		if (ret == 0) {