Input: ad7879 - add option to correct xy axis

Sebastian Zenker reported that driver swaps x and y samples when the
touchscreen leads are connected in accordance with the datasheet
specification.  Transposed axis can be typically corrected by touch
screen calibration however this bug also negatively influences touch
pressure measurements.

Add an option to correct x and y axis.
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Reported-and-tested-by: Sebastian Zenker <sebastian.zenker@gmx.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/ad7879.c

@@ -118,6 +118,7 @@ struct ad7879 {
 	unsigned int		irq;
 	bool			disabled;	/* P: input->mutex */
 	bool			suspended;	/* P: input->mutex */
+	bool			swap_xy;
 	u16			conversion_data[AD7879_NR_SENSE];
 	char			phys[32];
 	u8			first_conversion_delay;
@@ -161,6 +162,9 @@ static int ad7879_report(struct ad7879 *ts)
 	z1 = ts->conversion_data[AD7879_SEQ_Z1] & MAX_12BIT;
 	z2 = ts->conversion_data[AD7879_SEQ_Z2] & MAX_12BIT;
 
+	if (ts->swap_xy)
+		swap(x, y);
+
 	/*
 	 * The samples processed here are already preprocessed by the AD7879.
 	 * The preprocessing function consists of a median and an averaging
@@ -520,6 +524,7 @@ struct ad7879 *ad7879_probe(struct device *dev, u8 devid, unsigned int irq,
 	ts->dev = dev;
 	ts->input = input_dev;
 	ts->irq = irq;
+	ts->swap_xy = pdata->swap_xy;
 
 	setup_timer(&ts->timer, ad7879_timer, (unsigned long) ts);
 

include/linux/spi/ad7879.h

@@ -12,6 +12,8 @@ struct ad7879_platform_data {
 	u16	y_min, y_max;
 	u16	pressure_min, pressure_max;
 
+	bool	swap_xy;		/* swap x and y axes */
+
 	/* [0..255] 0=OFF Starts at 1=550us and goes
 	 * all the way to 9.440ms in steps of 35us.
 	 */