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>

2 files changed, 21 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index 103ee6ad299e..96581d08774f 100644
--- a/drivers/input/touchscreen/ads7846.c
+++ b/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";
diff --git a/include/linux/spi/ads7846.h b/include/linux/spi/ads7846.h
index a44fa7a02bd9..334d31411629 100644
--- a/include/linux/spi/ads7846.h
+++ b/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;