Input: adc-joystick - handle inverted axes

When one or more axes are inverted, (where min > max), normalize the
data so that min < max and invert the values reported to the input
stack.

This ensures we can continue defining the device correctly in the
device tree while not breaking downstream assumptions that min is
always less than max.
Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Acked-by: Artur Rojek <contact@artur-rojek.eu>
Link: https://lore.kernel.org/r/20240115192752.266367-1-macroalpha82@gmail.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/joystick/adc-joystick.c

@@ -18,6 +18,7 @@ struct adc_joystick_axis {
 	s32 range[2];
 	s32 fuzz;
 	s32 flat;
+	bool inverted;
 };
 
 struct adc_joystick {
@@ -29,6 +30,15 @@ struct adc_joystick {
 	bool polled;
 };
 
+static int adc_joystick_invert(struct input_dev *dev,
+			       unsigned int axis, int val)
+{
+	int min = input_abs_get_min(dev, axis);
+	int max = input_abs_get_max(dev, axis);
+
+	return (max + min) - val;
+}
+
 static void adc_joystick_poll(struct input_dev *input)
 {
 	struct adc_joystick *joy = input_get_drvdata(input);
@@ -38,6 +48,8 @@ static void adc_joystick_poll(struct input_dev *input)
 		ret = iio_read_channel_raw(&joy->chans[i], &val);
 		if (ret < 0)
 			return;
+		if (joy->axes[i].inverted)
+			val = adc_joystick_invert(input, i, val);
 		input_report_abs(input, joy->axes[i].code, val);
 	}
 	input_sync(input);
@@ -86,6 +98,8 @@ static int adc_joystick_handle(const void *data, void *private)
 			val = sign_extend32(val, msb);
 		else
 			val &= GENMASK(msb, 0);
+		if (joy->axes[i].inverted)
+			val = adc_joystick_invert(joy->input, i, val);
 		input_report_abs(joy->input, joy->axes[i].code, val);
 	}
 
@@ -168,6 +182,12 @@ static int adc_joystick_set_axes(struct device *dev, struct adc_joystick *joy)
 			goto err_fwnode_put;
 		}
 
+		if (axes[i].range[0] > axes[i].range[1]) {
+			dev_dbg(dev, "abs-axis %d inverted\n", i);
+			axes[i].inverted = true;
+			swap(axes[i].range[0], axes[i].range[1]);
+		}
+
 		fwnode_property_read_u32(child, "abs-fuzz", &axes[i].fuzz);
 		fwnode_property_read_u32(child, "abs-flat", &axes[i].flat);