From: Eric Miao <redacted>

Noises can be introduced when LCD signals are being driven, some platforms
provide a signal to assist the synchronization of this sampling procedure.

Signed-off-by: Eric Miao <redacted>
Cc: David Brownell <redacted>
Cc: Dmitry Torokhov <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/input/touchscreen/ads7846.c |   10 ++++++++++
 include/linux/spi/ads7846.h         |    2 ++
 2 files changed, 12 insertions(+)

diff -puN drivers/input/touchscreen/ads7846.c~input-ads7846-introduce-platform-specific-way-to-synchronize-sampling drivers/input/touchscreen/ads7846.c

--- a/drivers/input/touchscreen/ads7846.c~input-ads7846-introduce-platform-specific-way-to-synchronize-sampling
+++ a/drivers/input/touchscreen/ads7846.c

@@ -127,6 +127,8 @@ struct ads7846 {
 	void			(*filter_cleanup)(void *data);
 	int			(*get_pendown_state)(void);
 	int			gpio_pendown;
+
+	void			(*wait_for_sync)(void);
 };
 
 /* leave chip selected when we're done, for quicker re-select? */

@@ -511,6 +513,10 @@ static int get_pendown_state(struct ads7
 	return !gpio_get_value(ts->gpio_pendown);
 }
 
+static void null_wait_for_sync(void)
+{
+}
+
 /*
  * PENIRQ only kicks the timer.  The timer only reissues the SPI transfer,
  * to retrieve touchscreen status.

@@ -686,6 +692,7 @@ static void ads7846_rx_val(void *ads)
 	default:
 		BUG();
 	}
+	ts->wait_for_sync();
 	status = spi_async(ts->spi, m);
 	if (status)
 		dev_err(&ts->spi->dev, "spi_async --> %d\n",

@@ -723,6 +730,7 @@ static enum hrtimer_restart ads7846_time
 	} else {
 		/* pen is still down, continue with the measurement */
 		ts->msg_idx = 0;
+		ts->wait_for_sync();