Input: ads7846 - debouncing and rudimentary sample filtering

Some touchscreens seem to oscillate heavily for a while after touching
the screen.  Implement support for sampling the screen until we get two
consecutive values that are close enough.

Signed-off-by: Imre Deak <imre.deak@nokia.com>
Signed-off-by: Juha Yrjola <juha.yrjola@nokia.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

2 files changed, 121 insertions, 38 deletions

diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index 54d433477860..8670cd13bd5d 100644
--- a/drivers/input/touchscreen/ads7846.c
+++ b/drivers/input/touchscreen/ads7846.c
@@ -77,7 +77,13 @@ struct ads7846 {
         struct ts_event         tc;
 
         struct spi_transfer     xfer[10];
-        struct spi_message      msg;
+        struct spi_message      msg[5];
+        int                     msg_idx;
+        int                     read_cnt;
+        int                     last_read;
+
+        u16                     debounce_max;
+        u16                     debounce_tol;
 
         spinlock_t              lock;
         struct timer_list       timer;          /* P: lock */
@@ -167,7 +173,7 @@ static int ads7846_read12_ser(struct device *dev, unsigned command)
         if (!req)
                 return -ENOMEM;
 
-        INIT_LIST_HEAD(&req->msg.transfers);
+        spi_message_init(&req->msg);
 
         /* activate reference, so it has time to settle; */
         req->ref_on = REF_ON;
@@ -344,31 +350,76 @@ static void ads7846_rx(void *ads)
         spin_unlock_irqrestore(&ts->lock, flags);
 }
 
+static void ads7846_debounce(void *ads)
+{
+        struct ads7846          *ts = ads;
+        struct spi_message      *m;
+        struct spi_transfer     *t;
+        u16                     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;
+        } else {
+                /* Go for the next read */
+                ts->msg_idx++;
+                ts->read_cnt = 0;
+                m++;
+        }
+        status = spi_async(ts->spi, m);
+        if (status)
+                dev_err(&ts->spi->dev, "spi_async --> %d\n",
+                                status);
+}
+
 static void ads7846_timer(unsigned long handle)
 {
         struct ads7846  *ts = (void *)handle;
         int             status = 0;
-        unsigned long   flags;
+
+        ts->msg_idx = 0;
+        status = spi_async(ts->spi, &ts->msg[0]);
+        if (status)
+                dev_err(&ts->spi->dev, "spi_async --> %d\n", status);
+}
+
+static irqreturn_t ads7846_irq(int irq, void *handle, struct pt_regs *regs)
+{
+        struct ads7846 *ts = handle;
+        unsigned long flags;
+        int r = IRQ_HANDLED;
 
         spin_lock_irqsave(&ts->lock, flags);
-        if (!ts->pending) {
-                ts->pending = 1;
+        if (ts->irq_disabled)
+                r = IRQ_HANDLED;
+        else {
                 if (!ts->irq_disabled) {
+                        /* REVISIT irq logic for many ARM chips has cloned a
+                         * bug wherein disabling an irq in its handler won't
+                         * work;(it's disabled lazily, and too late to work.
+                         * until all their irq logic is fixed, we must shadow
+                         * that state here.
+                         */
                         ts->irq_disabled = 1;
+
                         disable_irq(ts->spi->irq);
                 }
-                status = spi_async(ts->spi, &ts->msg);
-                if (status)
-                        dev_err(&ts->spi->dev, "spi_async --> %d\n",
-                                        status);
+                if (!ts->pending) {
+                        ts->pending = 1;
+                        mod_timer(&ts->timer, jiffies);
+                }
         }
         spin_unlock_irqrestore(&ts->lock, flags);
-}
-
-static irqreturn_t ads7846_irq(int irq, void *handle, struct pt_regs *regs)
-{
-        ads7846_timer((unsigned long) handle);
-        return IRQ_HANDLED;
+        return r;
 }
 
 /*--------------------------------------------------------------------------*/
@@ -426,6 +477,7 @@ static int __devinit ads7846_probe(struct spi_device *spi)
         struct ads7846                  *ts;
         struct input_dev                *input_dev;
         struct ads7846_platform_data    *pdata = spi->dev.platform_data;
+        struct spi_message              *m;
         struct spi_transfer             *x;
         int                             err;
 
@@ -472,6 +524,8 @@ 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;
 
         snprintf(ts->phys, sizeof(ts->phys), "%s/input0", spi->dev.bus_id);
 
@@ -495,72 +549,98 @@ static int __devinit ads7846_probe(struct spi_device *spi)
         /* set up the transfers to read touchscreen state; this assumes we
          * use formula #2 for pressure, not #3.
          */
-        INIT_LIST_HEAD(&ts->msg.transfers);
+        m = &ts->msg[0];
         x = ts->xfer;
 
+        spi_message_init(m);
+
         /* y- still on; turn on only y+ (and ADC) */
         ts->read_y = READ_Y;
         x->tx_buf = &ts->read_y;
         x->len = 1;
-        spi_message_add_tail(x, &ts->msg);
+        spi_message_add_tail(x, m);
 
         x++;
         x->rx_buf = &ts->tc.y;
         x->len = 2;
-        spi_message_add_tail(x, &ts->msg);
+        spi_message_add_tail(x, m);
+
+        m->complete = ads7846_debounce;
+        m->context = ts;
+
+        m++;
+        spi_message_init(m);
+
+        /* turn y- off, x+ on, then leave in lowpower */
+        x++;
+        ts->read_x = READ_X;
+        x->tx_buf = &ts->read_x;
+        x->len = 1;
+        spi_message_add_tail(x, m);
+
+        x++;
+        x->rx_buf = &ts->tc.x;
+        x->len = 2;
+        spi_message_add_tail(x, m);
+
+        m->complete = ads7846_debounce;
+        m->context = ts;
 
         /* turn y+ off, x- on; we'll use formula #2 */
         if (ts->model == 7846) {
+                m++;
+                spi_message_init(m);
+
                 x++;
                 ts->read_z1 = READ_Z1;
                 x->tx_buf = &ts->read_z1;
                 x->len = 1;
-                spi_message_add_tail(x, &ts->msg);
+                spi_message_add_tail(x, m);
 
                 x++;
                 x->rx_buf = &ts->tc.z1;
                 x->len = 2;
-                spi_message_add_tail(x, &ts->msg);
+                spi_message_add_tail(x, m);
+
+                m->complete = ads7846_debounce;
+                m->context = ts;
+
+                m++;
+                spi_message_init(m);
 
                 x++;
                 ts->read_z2 = READ_Z2;
                 x->tx_buf = &ts->read_z2;
                 x->len = 1;
-                spi_message_add_tail(x, &ts->msg);
+                spi_message_add_tail(x, m);
 
                 x++;
                 x->rx_buf = &ts->tc.z2;
                 x->len = 2;
-                spi_message_add_tail(x, &ts->msg);
-        }
+                spi_message_add_tail(x, m);
 
-        /* turn y- off, x+ on, then leave in lowpower */
-        x++;
-        ts->read_x = READ_X;
-        x->tx_buf = &ts->read_x;
-        x->len = 1;
-        spi_message_add_tail(x, &ts->msg);
-
-        x++;
-        x->rx_buf = &ts->tc.x;
-        x->len = 2;
-        spi_message_add_tail(x, &ts->msg);
+                m->complete = ads7846_debounce;
+                m->context = ts;
+        }
 
         /* power down */
+        m++;
+        spi_message_init(m);
+
         x++;
         ts->pwrdown = PWRDOWN;
         x->tx_buf = &ts->pwrdown;
         x->len = 1;
-        spi_message_add_tail(x, &ts->msg);
+        spi_message_add_tail(x, m);
 
         x++;
         x->rx_buf = &ts->dummy;
         x->len = 2;
         CS_CHANGE(*x);
-        spi_message_add_tail(x, &ts->msg);
+        spi_message_add_tail(x, m);
 
-        ts->msg.complete = ads7846_rx;
-        ts->msg.context = ts;
+        m->complete = ads7846_rx;
+        m->context = ts;
 
         if (request_irq(spi->irq, ads7846_irq,
                         SA_SAMPLE_RANDOM | SA_TRIGGER_FALLING,
diff --git a/include/linux/spi/ads7846.h b/include/linux/spi/ads7846.h
index 72261e0f2ac1..3f7664951256 100644
--- a/include/linux/spi/ads7846.h
+++ b/include/linux/spi/ads7846.h
@@ -14,5 +14,8 @@ struct ads7846_platform_data {
         u16     x_min, x_max;
         u16     y_min, y_max;
         u16     pressure_min, pressure_max;
+
+        u16     debounce_max;           /* max number of readings per sample */
+        u16     debounce_tol;           /* tolerance used for filtering */
 };