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>
diff --git a/drivers/input/touchscreen/ad7879.c b/drivers/input/touchscreen/ad7879.c
index e2482b4..e607092 100644
--- a/drivers/input/touchscreen/ad7879.c
+++ b/drivers/input/touchscreen/ad7879.c
@@ -118,6 +118,7 @@
 	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 @@
 	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 @@
 	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);