[WIP] xpadneo, deadzones: Implement our own smooth dead zone

This commit sets flatness to zero to let us calculate the dead zone by
scaling the axis value instead of jumping out of it. The dead zone is
implemented as a smooth axial dead zone.

We also need to set fuzz to 0, otherwise `joydev` doesn't always return
to the center.

See-also: atar-axis#231
Signed-off-by: Kai Krakow <[email protected]>

hid-xpadneo/src/hid-xpadneo.c

@@ -942,10 +942,10 @@ static int xpadneo_input_configured(struct hid_device *hdev, struct hid_input *h
 
 	if (param_gamepad_compliance) {
 		hid_info(hdev, "enabling compliance with Linux Gamepad Specification\n");
-		input_set_abs_params(xdata->idev, ABS_X, -32768, 32767, 7, 4095);
-		input_set_abs_params(xdata->idev, ABS_Y, -32768, 32767, 7, 4095);
-		input_set_abs_params(xdata->idev, ABS_RX, -32768, 32767, 7, 4095);
-		input_set_abs_params(xdata->idev, ABS_RY, -32768, 32767, 7, 4095);
+		input_set_abs_params(xdata->idev, ABS_X, -32768, 32767, 0, 0);
+		input_set_abs_params(xdata->idev, ABS_Y, -32768, 32767, 0, 0);
+		input_set_abs_params(xdata->idev, ABS_RX, -32768, 32767, 0, 0);
+		input_set_abs_params(xdata->idev, ABS_RY, -32768, 32767, 0, 0);
 	}
 
 	/* combine triggers to form a rudder, use ABS_MISC to order after dpad */
@@ -954,8 +954,20 @@ static int xpadneo_input_configured(struct hid_device *hdev, struct hid_input *h
 	return 0;
 }
 
-static void xpadneo_report_abs(struct xpadneo_devdata *xdata, unsigned int code, int value) {
-	unsigned int offset = 0;
+static inline s32 scale_axis(s32 value, s32 zone) {
+	if (abs(value) < zone) {
+		value = 0;
+	} else {
+		s32 cleaned = (value < 0 ? value + zone : value - zone);
+		s32 scaled = 32767 * cleaned / (32767 - zone);
+		value = clamp(scaled, -32768, 32767);
+	}
+	return value;
+}
+
+static void xpadneo_report_abs(struct xpadneo_devdata *xdata, unsigned int code, s32 value) {
+	s32 offset = 0;
+	static u32 deadzone = 2560;
 
 	switch (code) {
 	case ABS_X:
@@ -972,18 +984,22 @@ static void xpadneo_report_abs(struct xpadneo_devdata *xdata, unsigned int code,
 	switch (code) {
 	case ABS_X:
 		xdata->abs.x = value;
+		value = scale_axis(value, deadzone);
 		break;
 	case ABS_Y:
 		xdata->abs.y = value;
+		value = scale_axis(value, deadzone);
 		break;
 	case ABS_Z:
 		xdata->abs.z = value;
 		break;
 	case ABS_RX:
 		xdata->abs.rx = value;
+		value = scale_axis(value, deadzone);
 		break;
 	case ABS_RY:
 		xdata->abs.ry = value;
+		value = scale_axis(value, deadzone);
 		break;
 	case ABS_RZ:
 		xdata->abs.rz = value;