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>

diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index 103ee6a..96581d0 100644 (file)
--- 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 a44fa7a..334d314 100644 (file)
--- 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;