Input: wm97xx-core - only schedule interrupt handler if not already scheduled

As well as clarifying the fact that the driver can cope if a second
interrupt occurs before the IRQ work is scheduled this also ensures
that calls to the machine irq_enable() are balanced, making that easier
to implement.  Normally this is redundant due to the interrupt disabling
but some unusal board configurations can trigger it.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/touchscreen/wm97xx-core.c

@@ -328,18 +328,18 @@ static void wm97xx_pen_irq_worker(struct work_struct *work)
  *
  * We have to disable the codec interrupt in the handler because it
  * can take upto 1ms to clear the interrupt source. We schedule a task
- * in a work queue to do the actual interaction with the chip (it
- * doesn't matter if we end up reenqueing it before it is executed
- * since we don't touch the chip until it has run).  The interrupt is
- * then enabled again in the slow handler when the source has been
- * cleared.
+ * in a work queue to do the actual interaction with the chip.  The
+ * interrupt is then enabled again in the slow handler when the source
+ * has been cleared.
  */
 static irqreturn_t wm97xx_pen_interrupt(int irq, void *dev_id)
 {
 	struct wm97xx *wm = dev_id;
 
-	wm->mach_ops->irq_enable(wm, 0);
-	queue_work(wm->ts_workq, &wm->pen_event_work);
+	if (!work_pending(&wm->pen_event_work)) {
+		wm->mach_ops->irq_enable(wm, 0);
+		queue_work(wm->ts_workq, &wm->pen_event_work);
+	}
 
 	return IRQ_HANDLED;
 }