From: Chris Morgan <redacted>

Add a helper function to make it easier for a driver to invert abs
values when needed. It is up to the driver itself to track axes that
need to be inverted and normalize the data before it is passed on.

This function assumes that drivers will set the min and max values
so that min < max and then will simply call this function each time
the values need to be inverted.

Signed-off-by: Chris Morgan <redacted>
---
 drivers/input/input.c | 19 +++++++++++++++++++
 include/linux/input.h |  1 +
 2 files changed, 20 insertions(+)

diff --git a/drivers/input/input.c b/drivers/input/input.c
index 8c5fdb0f858a..f135aed165a1 100644
--- a/drivers/input/input.c
+++ b/drivers/input/input.c

@@ -552,6 +552,25 @@ void input_copy_abs(struct input_dev *dst, unsigned int dst_axis,
 }
 EXPORT_SYMBOL(input_copy_abs);
 
+/**
+ * input_invert_abs - Invert the abs value for an inverted axis.
+ * @dev: Input device with absolute events
+ * @axis: ABS_* value selecting the destination axis for the event to
+ *	  invert.
+ * @val: Value to be inverted based on min and max values of the axis.
+ *
+ * Return an inverted value for a given ABS axis based on its min and
+ * max values.
+ */
+int input_invert_abs(struct input_dev *dev, unsigned int axis, int val)
+{
+	int min = dev->absinfo[axis].minimum;
+	int max = dev->absinfo[axis].maximum;
+
+	return (max + min) - val;