Input: atkbd - throttle LED switching

On some boxes keyboard controllers are too slow to withstand
continuous flow of requests to turn keyboard LEDs on and off
and start losing some keypresses or even all of them.

Delay executing of LED switching request if we had another one
within 50 ms thus easing load on the controller.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/keyboard/atkbd.c

@@ -219,7 +219,8 @@ struct atkbd {
 	unsigned long time;
 	unsigned long err_count;
 
-	struct work_struct event_work;
+	struct delayed_work event_work;
+	unsigned long event_jiffies;
 	struct mutex event_mutex;
 	unsigned long event_mask;
 };
@@ -565,7 +566,7 @@ static int atkbd_set_leds(struct atkbd *atkbd)
 
 static void atkbd_event_work(struct work_struct *work)
 {
-	struct atkbd *atkbd = container_of(work, struct atkbd, event_work);
+	struct atkbd *atkbd = container_of(work, struct atkbd, event_work.work);
 
 	mutex_lock(&atkbd->event_mutex);
 
@@ -578,13 +579,31 @@ static void atkbd_event_work(struct work_struct *work)
 	mutex_unlock(&atkbd->event_mutex);
 }
 
+/*
+ * Schedule switch for execution. We need to throttle requests,
+ * otherwise keyboard may become unresponsive.
+ */
+static void atkbd_schedule_event_work(struct atkbd *atkbd, int event_bit)
+{
+	unsigned long delay = msecs_to_jiffies(50);
+
+	if (time_after(jiffies, atkbd->event_jiffies + delay))
+		delay = 0;
+
+	atkbd->event_jiffies = jiffies;
+	set_bit(event_bit, &atkbd->event_mask);
+	wmb();
+	schedule_delayed_work(&atkbd->event_work, delay);
+}
+
 /*
  * Event callback from the input module. Events that change the state of
  * the hardware are processed here. If action can not be performed in
  * interrupt context it is offloaded to atkbd_event_work.
  */
 
-static int atkbd_event(struct input_dev *dev, unsigned int type, unsigned int code, int value)
+static int atkbd_event(struct input_dev *dev,
+			unsigned int type, unsigned int code, int value)
 {
 	struct atkbd *atkbd = input_get_drvdata(dev);
 
@@ -594,19 +613,12 @@ static int atkbd_event(struct input_dev *dev, unsigned int type, unsigned int co
 	switch (type) {
 
 		case EV_LED:
-			set_bit(ATKBD_LED_EVENT_BIT, &atkbd->event_mask);
-			wmb();
-			schedule_work(&atkbd->event_work);
+			atkbd_schedule_event_work(atkbd, ATKBD_LED_EVENT_BIT);
 			return 0;
 
 		case EV_REP:
-
-			if (!atkbd->softrepeat) {
-				set_bit(ATKBD_REP_EVENT_BIT, &atkbd->event_mask);
-				wmb();
-				schedule_work(&atkbd->event_work);
-			}
-
+			if (!atkbd->softrepeat)
+				atkbd_schedule_event_work(atkbd, ATKBD_REP_EVENT_BIT);
 			return 0;
 	}
 
@@ -940,7 +952,7 @@ static int atkbd_connect(struct serio *serio, struct serio_driver *drv)
 
 	atkbd->dev = dev;
 	ps2_init(&atkbd->ps2dev, serio);
-	INIT_WORK(&atkbd->event_work, atkbd_event_work);
+	INIT_DELAYED_WORK(&atkbd->event_work, atkbd_event_work);
 	mutex_init(&atkbd->event_mutex);
 
 	switch (serio->id.type) {