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>

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);
 };