Input: serio - add fast reconnect option

Devices connected to serio bus are quite slow, and to improve apparent
speed of resume process, serio core resumes (reconnects) its devices
asynchronously, by posting port reconnect requests to a workqueue.
Unfortunately this means that if there is a dependent device of a given
serio port (for example SMBus part of touchpad connected via both PS/2 and
SMBus), we do not have a good way of ensuring resume order.

This change allows drivers to define "fast reconnect" handlers that would
be called in-line during system resume. Drivers need to ensure that these
handlers are truly "fast".
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/serio/serio.c

@@ -953,12 +953,24 @@ static int serio_suspend(struct device *dev)
 static int serio_resume(struct device *dev)
 {
 	struct serio *serio = to_serio_port(dev);
+	int error = -ENOENT;
 
-	/*
-	 * Driver reconnect can take a while, so better let kseriod
-	 * deal with it.
-	 */
-	serio_queue_event(serio, NULL, SERIO_RECONNECT_PORT);
+	mutex_lock(&serio->drv_mutex);
+	if (serio->drv && serio->drv->fast_reconnect) {
+		error = serio->drv->fast_reconnect(serio);
+		if (error && error != -ENOENT)
+			dev_warn(dev, "fast reconnect failed with error %d\n",
+				 error);
+	}
+	mutex_unlock(&serio->drv_mutex);
+
+	if (error) {
+		/*
+		 * Driver reconnect can take a while, so better let
+		 * kseriod deal with it.
+		 */
+		serio_queue_event(serio, NULL, SERIO_RECONNECT_PORT);
+	}
 
 	return 0;
 }

include/linux/serio.h

@@ -77,6 +77,7 @@ struct serio_driver {
 	irqreturn_t (*interrupt)(struct serio *, unsigned char, unsigned int);
 	int  (*connect)(struct serio *, struct serio_driver *drv);
 	int  (*reconnect)(struct serio *);
+	int  (*fast_reconnect)(struct serio *);
 	void (*disconnect)(struct serio *);
 	void (*cleanup)(struct serio *);