linux-kernel - [PATCH v2] HID: playstation: Center initial joystick axes to prevent spurious events

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Message-ID: <20251111234519.369652-1-svv@google.com>
Date: Tue, 11 Nov 2025 15:45:19 -0800
From: Siarhei Vishniakou <svv@...gle.com>
To: Jiri Kosina <jikos@...nel.org>, Benjamin Tissoires <bentiss@...nel.org>, 
	Roderick Colenbrander <roderick.colenbrander@...y.com>, linux-input@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Cc: Siarhei Vishniakou <svv@...gle.com>
Subject: [PATCH v2] HID: playstation: Center initial joystick axes to prevent
 spurious events

When a new PlayStation gamepad (DualShock 4 or DualSense) is initialized,
the input subsystem sets the default value for its absolute axes (e.g.,
ABS_X, ABS_Y) to 0.

However, the hardware's actual neutral/resting state for these joysticks
is 128 (0x80). This creates a mismatch.

When the first HID report arrives from the device, the driver sees the
resting value of 128. The kernel compares this to its initial state of 0
and incorrectly interprets this as a delta (0 -> 128). Consequently, it
generates EV_ABS events for this initial, non-existent movement.

This behavior can fail userspace 'sanity check' tests (e.g., in
Android CTS) that correctly assert no motion events should be generated
from a device that is already at rest.

This patch fixes the issue by explicitly setting the initial value of the
main joystick axes (e.g., ABS_X, ABS_Y, ABS_RX, ABS_RY) to 128 (0x80)
in the common ps_gamepad_create() function.

This aligns the kernel's initial state with the hardware's expected
neutral state, ensuring that the first report (at 128) produces no
delta and thus, no spurious event.

Signed-off-by: Siarhei Vishniakou <svv@...gle.com>
---
 drivers/hid/hid-playstation.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/hid/hid-playstation.c b/drivers/hid/hid-playstation.c
index 1468fb11e39d..a145b5ea4405 100644
--- a/drivers/hid/hid-playstation.c
+++ b/drivers/hid/hid-playstation.c
@@ -718,11 +718,16 @@ static struct input_dev *ps_gamepad_create(struct hid_device *hdev,
 	if (IS_ERR(gamepad))
 		return ERR_CAST(gamepad);

+	/* Set initial resting state for joysticks to 128 (center) */
 	input_set_abs_params(gamepad, ABS_X, 0, 255, 0, 0);
+	gamepad->absinfo[ABS_X].value = 128;
 	input_set_abs_params(gamepad, ABS_Y, 0, 255, 0, 0);
+	gamepad->absinfo[ABS_Y].value = 128;
 	input_set_abs_params(gamepad, ABS_Z, 0, 255, 0, 0);
 	input_set_abs_params(gamepad, ABS_RX, 0, 255, 0, 0);
+	gamepad->absinfo[ABS_RX].value = 128;
 	input_set_abs_params(gamepad, ABS_RY, 0, 255, 0, 0);
+	gamepad->absinfo[ABS_RY].value = 128;
 	input_set_abs_params(gamepad, ABS_RZ, 0, 255, 0, 0);

 	input_set_abs_params(gamepad, ABS_HAT0X, -1, 1, 0, 0);
-- 
2.51.2.1041.gc1ab5b90ca-goog