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>

diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index 1aaa153..1494175 100644 (file)
--- 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 d8823e2..adb3daf 100644 (file)
--- 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);
 };