[PATCH] HID: playstation: Remap joystick axes to be centered at 0

[Siarhei Vishniakou <svv@google.com>]

The joystick axes (ABS_X, ABS_Y, ABS_RX, ABS_RY) for PlayStation
gamepads report a neutral state of 128 over HID, with a full range of
[0, 255]. The driver previously mapped this directly, resulting in an
evdev range of [0, 255] with a resting point of 128.

This approach is unconventional for Linux gamepad drivers and has several
drawbacks: it requires userspace applications to be aware of the
non-zero resting state, and it is incompatible with the input
subsystem's 'flat' (deadzone) logic, which assumes a resting point of 0.

This patch remaps the four joystick axes to the conventional signed
8-bit range of [-128, 127], with 0 as the neutral state. This is
accomplished by changing their evdev range in ps_gamepad_create() and
translating the incoming hardware value in the report parsing functions
by subtracting 128.

The analog trigger axes (ABS_Z, ABS_RZ) are handled separately. Their
resting state is 0 (un-pressed), and their hardware range of [0, 255]
is already the conventional representation. They are left unmodified by
this patch.

This makes the joystick behavior consistent with other gamepad drivers
while preserving the standard behavior for the triggers.

Signed-off-by: Siarhei Vishniakou <svv@google.com>
---
 drivers/hid/hid-playstation.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/drivers/hid/hid-playstation.c b/drivers/hid/hid-playstation.c
index 1468fb11e39d..ca5bca9c2654 100644
--- a/drivers/hid/hid-playstation.c
+++ b/drivers/hid/hid-playstation.c
@@ -718,11 +718,11 @@ static struct input_dev *ps_gamepad_create(struct hid_device *hdev,
 	if (IS_ERR(gamepad))
 		return ERR_CAST(gamepad);
 
-	input_set_abs_params(gamepad, ABS_X, 0, 255, 0, 0);
-	input_set_abs_params(gamepad, ABS_Y, 0, 255, 0, 0);
+	input_set_abs_params(gamepad, ABS_X, -128, 127, 0, 0);
+	input_set_abs_params(gamepad, ABS_Y, -128, 127, 0, 0);
 	input_set_abs_params(gamepad, ABS_Z, 0, 255, 0, 0);
-	input_set_abs_params(gamepad, ABS_RX, 0, 255, 0, 0);
-	input_set_abs_params(gamepad, ABS_RY, 0, 255, 0, 0);
+	input_set_abs_params(gamepad, ABS_RX, -128, 127, 0, 0);
+	input_set_abs_params(gamepad, ABS_RY, -128, 127, 0, 0);
 	input_set_abs_params(gamepad, ABS_RZ, 0, 255, 0, 0);
 
 	input_set_abs_params(gamepad, ABS_HAT0X, -1, 1, 0, 0);
@@ -1349,10 +1349,10 @@ static int dualsense_parse_report(struct ps_device *ps_dev, struct hid_report *r
 		return -1;
 	}
 
-	input_report_abs(ds->gamepad, ABS_X,  ds_report->x);
-	input_report_abs(ds->gamepad, ABS_Y,  ds_report->y);
-	input_report_abs(ds->gamepad, ABS_RX, ds_report->rx);
-	input_report_abs(ds->gamepad, ABS_RY, ds_report->ry);
+	input_report_abs(ds->gamepad, ABS_X,  ds_report->x - 128);
+	input_report_abs(ds->gamepad, ABS_Y,  ds_report->y - 128);
+	input_report_abs(ds->gamepad, ABS_RX, ds_report->rx - 128);
+	input_report_abs(ds->gamepad, ABS_RY, ds_report->ry - 128);
 	input_report_abs(ds->gamepad, ABS_Z,  ds_report->z);
 	input_report_abs(ds->gamepad, ABS_RZ, ds_report->rz);
 
@@ -2272,10 +2272,10 @@ static int dualshock4_parse_report(struct ps_device *ps_dev, struct hid_report *
 		return -1;
 	}
 
-	input_report_abs(ds4->gamepad, ABS_X,  ds4_report->x);
-	input_report_abs(ds4->gamepad, ABS_Y,  ds4_report->y);
-	input_report_abs(ds4->gamepad, ABS_RX, ds4_report->rx);
-	input_report_abs(ds4->gamepad, ABS_RY, ds4_report->ry);
+	input_report_abs(ds4->gamepad, ABS_X,  ds4_report->x - 128);
+	input_report_abs(ds4->gamepad, ABS_Y,  ds4_report->y - 128);
+	input_report_abs(ds4->gamepad, ABS_RX, ds4_report->rx - 128);
+	input_report_abs(ds4->gamepad, ABS_RY, ds4_report->ry - 128);
 	input_report_abs(ds4->gamepad, ABS_Z,  ds4_report->z);
 	input_report_abs(ds4->gamepad, ABS_RZ, ds4_report->rz);
 
-- 
2.51.0.740.g6adb054d12-goog