Input: ads7846 - improve filtering for thumb press accuracy

Providing more accurate coordinates for thumb press requires additional
steps in the filtering logic:

- Ignore samples found invalid by the debouncing logic, or the ones that
  have out of bound pressure value.
- Add a parameter to repeat debouncing, so that more then two consecutive
  good readings are required for a valid sample.

Signed-off-by: Imre Deak <imre.deak@nokia.com>
Acked-by: Juha Yrjola <juha.yrjola@nokia.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

2 files changed, 61 insertions, 17 deletions

diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index 1aaa153a2774..1494175ac6fe 100644
--- a/drivers/input/touchscreen/ads7846.c
+++ b/drivers/input/touchscreen/ads7846.c
@@ -71,6 +71,7 @@ struct ts_event {
         __be16 x;
         __be16 y;
         __be16 z1, z2;
+        int    ignore;
 };
 
 struct ads7846 {
@@ -81,6 +82,7 @@ struct ads7846 {
         u16                     model;
         u16                     vref_delay_usecs;
         u16                     x_plate_ohms;
+        u16                     pressure_max;
 
         u8                      read_x, read_y, read_z1, read_z2, pwrdown;
         u16                     dummy;          /* for the pwrdown read */
@@ -88,12 +90,15 @@ struct ads7846 {
 
         struct spi_transfer     xfer[10];
         struct spi_message      msg[5];
+        struct spi_message      *last_msg;
         int                     msg_idx;
         int                     read_cnt;
+        int                     read_rep;
         int                     last_read;
 
         u16                     debounce_max;
         u16                     debounce_tol;
+        u16                     debounce_rep;
 
         spinlock_t              lock;
         struct timer_list       timer;          /* P: lock */
@@ -354,6 +359,14 @@ static void ads7846_rx(void *ads)
         } else
                 Rt = 0;
 
+        /* Sample found inconsistent by debouncing or pressure is beyond
+        * the maximum. Don't report it to user space, repeat at least
+        * once more the measurement */
+        if (ts->tc.ignore || Rt > ts->pressure_max) {
+                mod_timer(&ts->timer, jiffies + TS_POLL_PERIOD);
+                return;
+        }
+
         /* NOTE:  "pendown" is inferred from pressure; we don't rely on
          * being able to check nPENIRQ status, or "friendly" trigger modes
          * (both-edges is much better than just-falling or low-level).
@@ -402,25 +415,45 @@ static void ads7846_debounce(void *ads)
         struct ads7846          *ts = ads;
         struct spi_message      *m;
         struct spi_transfer     *t;
-        u16                     val;
+        int                     val;
         int                     status;
 
         m = &ts->msg[ts->msg_idx];
         t = list_entry(m->transfers.prev, struct spi_transfer, transfer_list);
         val = (*(u16 *)t->rx_buf) >> 3;
-
-        if (!ts->read_cnt || (abs(ts->last_read - val) > ts->debounce_tol
-                                && ts->read_cnt < ts->debounce_max)) {
-                /* Repeat it, if this was the first read or the read wasn't
-                 * consistent enough
-                 */
-                ts->read_cnt++;
-                ts->last_read = val;
+        if (!ts->read_cnt || (abs(ts->last_read - val) > ts->debounce_tol)) {
+                /* Repeat it, if this was the first read or the read
+                 * wasn't consistent enough. */
+                if (ts->read_cnt < ts->debounce_max) {
+                        ts->last_read = val;
+                        ts->read_cnt++;
+                } else {
+                        /* Maximum number of debouncing reached and still
+                         * not enough number of consistent readings. Abort
+                         * the whole sample, repeat it in the next sampling
+                         * period.
+                         */
+                        ts->tc.ignore = 1;
+                        ts->read_cnt = 0;
+                        /* Last message will contain ads7846_rx() as the
+                         * completion function.
+                         */
+                        m = ts->last_msg;
+                }
+                /* Start over collecting consistent readings. */
+                ts->read_rep = 0;
         } else {
-                /* Go for the next read */
-                ts->msg_idx++;
-                ts->read_cnt = 0;
-                m++;
+                if (++ts->read_rep > ts->debounce_rep) {
+                        /* Got a good reading for this coordinate,
+                         * go for the next one. */
+                        ts->tc.ignore = 0;
+                        ts->msg_idx++;
+                        ts->read_cnt = 0;
+                        ts->read_rep = 0;
+                        m++;
+                } else
+                        /* Read more values that are consistent. */
+                        ts->read_cnt++;
         }
         status = spi_async(ts->spi, m);
         if (status)
@@ -609,8 +642,15 @@ static int __devinit ads7846_probe(struct spi_device *spi)
         ts->model = pdata->model ? : 7846;
         ts->vref_delay_usecs = pdata->vref_delay_usecs ? : 100;
         ts->x_plate_ohms = pdata->x_plate_ohms ? : 400;
-        ts->debounce_max = pdata->debounce_max ? : 1;
-        ts->debounce_tol = pdata->debounce_tol ? : 10;
+        ts->pressure_max = pdata->pressure_max ? : ~0;
+        if (pdata->debounce_max) {
+                ts->debounce_max = pdata->debounce_max;
+                ts->debounce_tol = pdata->debounce_tol;
+                ts->debounce_rep = pdata->debounce_rep;
+                if (ts->debounce_rep > ts->debounce_max + 1)
+                        ts->debounce_rep = ts->debounce_max - 1;
+        } else
+                ts->debounce_tol = ~0;
         ts->get_pendown_state = pdata->get_pendown_state;
 
         snprintf(ts->phys, sizeof(ts->phys), "%s/input0", spi->dev.bus_id);
@@ -728,6 +768,8 @@ static int __devinit ads7846_probe(struct spi_device *spi)
         m->complete = ads7846_rx;
         m->context = ts;
 
+        ts->last_msg = m;
+
         if (request_irq(spi->irq, ads7846_irq,
                         SA_SAMPLE_RANDOM | SA_TRIGGER_FALLING,
                         spi->dev.bus_id, ts)) {
diff --git a/include/linux/spi/ads7846.h b/include/linux/spi/ads7846.h
index d8823e237e0b..adb3dafd33e9 100644
--- a/include/linux/spi/ads7846.h
+++ b/include/linux/spi/ads7846.h
@@ -15,9 +15,11 @@ struct ads7846_platform_data {
         u16     y_min, y_max;
         u16     pressure_min, pressure_max;
 
-        u16     debounce_max;           /* max number of readings per sample */
+        u16     debounce_max;           /* max number of additional readings
+                                         * per sample */
         u16     debounce_tol;           /* tolerance used for filtering */
-
+        u16     debounce_rep;           /* additional consecutive good readings
+                                         * required after the first two */
         int     (*get_pendown_state)(void);
 };