2 files changed, 72 insertions, 1 deletions

diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
index 1c9069cd3bae..103ee6ad299e 100644
--- a/drivers/input/touchscreen/ads7846.c
+++ b/drivers/input/touchscreen/ads7846.c
@@ -95,7 +95,7 @@ struct ads7846 {
         u16                     dummy;          /* for the pwrdown read */
         struct ts_event         tc;
 
-        struct spi_transfer     xfer[10];
+        struct spi_transfer     xfer[18];
         struct spi_message      msg[5];
         struct spi_message      *last_msg;
         int                     msg_idx;
@@ -936,6 +936,24 @@ static int __devinit ads7846_probe(struct spi_device *spi)
         x->len = 2;
         spi_message_add_tail(x, m);
 
+        /* the first sample after switching drivers can be low quality;
+         * optionally discard it, using a second one after the signals
+         * have had enough time to stabilize.
+         */
+        if (pdata->settle_delay_usecs) {
+                x->delay_usecs = pdata->settle_delay_usecs;
+
+                x++;
+                x->tx_buf = &ts->read_y;
+                x->len = 1;
+                spi_message_add_tail(x, m);
+
+                x++;
+                x->rx_buf = &ts->tc.y;
+                x->len = 2;
+                spi_message_add_tail(x, m);
+        }
+
         m->complete = ads7846_rx_val;
         m->context = ts;
 
@@ -954,6 +972,21 @@ static int __devinit ads7846_probe(struct spi_device *spi)
         x->len = 2;
         spi_message_add_tail(x, m);
 
+        /* ... maybe discard first sample ... */
+        if (pdata->settle_delay_usecs) {
+                x->delay_usecs = pdata->settle_delay_usecs;
+
+                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_rx_val;
         m->context = ts;
 
@@ -973,6 +1006,21 @@ static int __devinit ads7846_probe(struct spi_device *spi)
                 x->len = 2;
                 spi_message_add_tail(x, m);
 
+                /* ... maybe discard first sample ... */
+                if (pdata->settle_delay_usecs) {
+                        x->delay_usecs = pdata->settle_delay_usecs;
+
+                        x++;
+                        x->tx_buf = &ts->read_z1;
+                        x->len = 1;
+                        spi_message_add_tail(x, m);
+
+                        x++;
+                        x->rx_buf = &ts->tc.z1;
+                        x->len = 2;
+                        spi_message_add_tail(x, m);
+                }
+
                 m->complete = ads7846_rx_val;
                 m->context = ts;
 
@@ -990,6 +1038,21 @@ static int __devinit ads7846_probe(struct spi_device *spi)
                 x->len = 2;
                 spi_message_add_tail(x, m);
 
+                /* ... maybe discard first sample ... */
+                if (pdata->settle_delay_usecs) {
+                        x->delay_usecs = pdata->settle_delay_usecs;
+
+                        x++;
+                        x->tx_buf = &ts->read_z2;
+                        x->len = 1;
+                        spi_message_add_tail(x, m);
+
+                        x++;
+                        x->rx_buf = &ts->tc.z2;
+                        x->len = 2;
+                        spi_message_add_tail(x, m);
+                }
+
                 m->complete = ads7846_rx_val;
                 m->context = ts;
         }
diff --git a/include/linux/spi/ads7846.h b/include/linux/spi/ads7846.h
index 3387e44dfd13..a44fa7a02bd9 100644
--- a/include/linux/spi/ads7846.h
+++ b/include/linux/spi/ads7846.h
@@ -16,6 +16,14 @@ struct ads7846_platform_data {
         u16     vref_delay_usecs;       /* 0 for external vref; etc */
         int     keep_vref_on:1;         /* set to keep vref on for differential
                                          * measurements as well */
+
+        /* Settling time of the analog signals; a function of Vcc and the
+         * capacitance on the X/Y drivers.  If set to non-zero, two samples
+         * are taken with settle_delay us apart, and the second one is used.
+         * ~150 uSec with 0.01uF caps.
+         */
+        u16     settle_delay_usecs;
+
         u16     x_plate_ohms;
         u16     y_plate_ohms;