wake up from a serial port

Enable wakeup from serial ports, make it run-time configurable over sysfs,
e.g.,

echo enabled > /sys/devices/platform/serial8250.0/tty/ttyS0/power/wakeup

Requires

# CONFIG_SYSFS_DEPRECATED is not set

Following suggestions from Alan and Russell moved the may_wake_up checks
to serial_core.c. This time actually tested - it does even work. Could
someone, please, verify, that put_device after device_find_child is
correct?

Also would be nice to test with a Natsemi UART, that can wake up the system,
if such systems exist.

For this you just have to apply the patch below, issue the above "echo"
command to one of your Natsemi port, suspend and resume your system, and
verify that your Natsemi port still works. If you are actually capable of
waking up the system from that port, would be nice to test that as well.

Signed-off-by: Guennadi Liakhovetski <[e-mail]>
Cc: Alan Cox <[e-mail]>
Cc: Russell King <[e-mail]>
Cc: Kay Sievers <[e-mail]>
Cc: Greg KH <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/serial/serial_core.c

···
 	}
 }
 
+struct uart_match {
+	struct uart_port *port;
+	struct uart_driver *driver;
+};
+
+static int serial_match_port(struct device *dev, void *data)
+{
+	struct uart_match *match = data;
+	dev_t devt = MKDEV(match->driver->major, match->driver->minor) + match->port->line;
+
+	return dev->devt == devt; /* Actually, only one tty per port */
+}
+
 int uart_suspend_port(struct uart_driver *drv, struct uart_port *port)
 {
 	struct uart_state *state = drv->state + port->line;
+	struct device *tty_dev;
+	struct uart_match match = {port, drv};
 
 	mutex_lock(&state->mutex);
 
···
 		return 0;
 	}
 #endif
+
+	tty_dev = device_find_child(port->dev, &match, serial_match_port);
+	if (device_may_wakeup(tty_dev)) {
+		enable_irq_wake(port->irq);
+		put_device(tty_dev);
+		mutex_unlock(&state->mutex);
+		return 0;
+	}
+	port->suspended = 1;
 
 	if (state->info && state->info->flags & UIF_INITIALIZED) {
 		const struct uart_ops *ops = port->ops;
···
 		return 0;
 	}
 #endif
+
+	if (!port->suspended) {
+		disable_irq_wake(port->irq);
+		mutex_unlock(&state->mutex);
+		return 0;
+	}
+	port->suspended = 0;
 
 	uart_change_pm(state, 0);
 
···
 {
 	struct uart_state *state;
 	int ret = 0;
+	struct device *tty_dev;
 
 	BUG_ON(in_interrupt());
 
···
 	 * Register the port whether it's detected or not.  This allows
 	 * setserial to be used to alter this ports parameters.
 	 */
-	tty_register_device(drv->tty_driver, port->line, port->dev);
+	tty_dev = tty_register_device(drv->tty_driver, port->line, port->dev);
+	if (likely(!IS_ERR(tty_dev))) {
+		device_can_wakeup(tty_dev) = 1;
+		device_set_wakeup_enable(tty_dev, 0);
+	} else
+		printk(KERN_ERR "Cannot register tty device on line %d\n",
+		       port->line);
 
 	/*
 	 * Ensure UPF_DEAD is not set.

include/linux/serial_core.h

···
 	resource_size_t		mapbase;		/* for ioremap */
 	struct device		*dev;			/* parent device */
 	unsigned char		hub6;			/* this should be in the 8250 driver */
-	unsigned char		unused[3];
+	unsigned char		suspended;
+	unsigned char		unused[2];
 	void			*private_data;		/* generic platform data pointer */
 };