Input: ads7846 - re-check pendown status before reporting events

Pendown status from the PENIRQ pin is currently read only at the beginning
of a sample set. If the pen is lifted just after sampling has began then
sampled values become wrong.

This patch adds an optional platform penirq_recheck_delay attribute.  If
non-zero, samples are only reported to the input subsystem if PENIRQ is
still active that long after the samples taken.

Signed-off-by: Semih Hazar <semih.hazar@indefia.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/touchscreen/ads7846.c

@@ -107,6 +107,8 @@ struct ads7846 {
 	u16			debounce_tol;
 	u16			debounce_rep;
 
+	u16			penirq_recheck_delay_usecs;
+
 	spinlock_t		lock;
 	struct hrtimer		timer;
 	unsigned		pendown:1;	/* P: lock */
@@ -553,6 +555,15 @@ static void ads7846_rx(void *ads)
 		return;
 	}
 
+	/* Maybe check the pendown state before reporting. This discards
+	 * false readings when the pen is lifted.
+	 */
+	if (ts->penirq_recheck_delay_usecs) {
+		udelay(ts->penirq_recheck_delay_usecs);
+		if (!ts->get_pendown_state())
+			Rt = 0;
+	}
+
 	/* NOTE: We can't rely on the pressure to determine the pen down
 	 * state, even this controller has a pressure sensor.  The pressure
 	 * value can fluctuate for quite a while after lifting the pen and
@@ -896,6 +907,10 @@ static int __devinit ads7846_probe(struct spi_device *spi)
 		ts->filter = ads7846_no_filter;
 	ts->get_pendown_state = pdata->get_pendown_state;
 
+	if (pdata->penirq_recheck_delay_usecs)
+		ts->penirq_recheck_delay_usecs =
+				pdata->penirq_recheck_delay_usecs;
+
 	snprintf(ts->phys, sizeof(ts->phys), "%s/input0", spi->dev.bus_id);
 
 	input_dev->name = "ADS784x Touchscreen";

include/linux/spi/ads7846.h

@@ -24,6 +24,12 @@ struct ads7846_platform_data {
 	 */
 	u16	settle_delay_usecs;
 
+	/* If set to non-zero, after samples are taken this delay is applied
+	 * and penirq is rechecked, to help avoid false events.  This value
+	 * is affected by the material used to build the touch layer.
+	 */
+	u16	penirq_recheck_delay_usecs;
+
 	u16	x_plate_ohms;
 	u16	y_plate_ohms;