[PATCH v2 09/12] HID: asus: add support to force feedback

[Denis Benato <denis.benato@linux.dev>]

Unlike ROG ally the X version and following ones uses DInput protocol
and the force feedback needs to be implemented as its protocol is
vendor-specific, therefore add support for FF_RUMBLE with magnitude
scaling on a work-queue based approach to avoid using possibly
sleeping calls in atomic context.

Assisted-by: opencode:glm-5.2
Assisted-by: VSCode:gpt-5.3-codex
Signed-off-by: Denis Benato <denis.benato@linux.dev>
Signed-off-by: Khamunetri Clark <khamunetriclark@gmail.com>
Signed-off-by: Luke Jones <luke@ljones.dev>
---
 drivers/hid/hid-asus.c | 198 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 191 insertions(+), 7 deletions(-)

diff --git a/drivers/hid/hid-asus.c b/drivers/hid/hid-asus.c
index 6f43b7317168..ca3050fea843 100644
--- a/drivers/hid/hid-asus.c
+++ b/drivers/hid/hid-asus.c
@@ -235,6 +235,23 @@ struct ally_config {
 	struct ally_joystick_resp_curve right_curve;
 };
 
+/* XInput force-feedback report (output report 0x0d, gamepad interface) */
+struct ff_data {
+	u8 enable;
+	u8 magnitude_left;
+	u8 magnitude_right;
+	u8 magnitude_strong;
+	u8 magnitude_weak;
+	u8 pulse_sustain_10ms;
+	u8 pulse_release_10ms;
+	u8 loop_count;
+} __packed;
+
+struct ff_report {
+	u8 report_id;
+	struct ff_data ff;
+} __packed;
+
 struct ally_handheld {
 	/* All read/write to IN interfaces must lock */
 	struct mutex intf_mutex;
@@ -243,6 +260,13 @@ struct ally_handheld {
 	struct input_dev *ally_x_input;
 	struct hid_device *ally_x_hdev;
 
+	struct ff_report ff_packet;
+	struct work_struct ff_work;
+	/* Serializes ff_packet and update_ff between play_effect and ff_work */
+	spinlock_t ff_lock;
+	bool ff_work_initialized;
+	bool update_ff;
+
 	struct hid_device *keyboard_hdev;
 	struct input_dev *keyboard_input;
 
@@ -357,9 +381,13 @@ enum ally_command_codes {
 	CMD_SET_ANTI_DEADZONE           = 0x18,
 };
 
+/* XInput rumble magnitudes use the hardware's 0..100 intensity range. */
+#define ALLY_FF_MAX_INTENSITY 100
+
 static const u8 ALLY_FORCE_FEEDBACK_OFF[] = {
 	0x0D, 0x0F, 0x00, 0x00, 0x00, 0x00, 0xFF, 0x00, 0xEB
 };
+static_assert(sizeof(struct ff_report) == sizeof(ALLY_FORCE_FEEDBACK_OFF));
 
 /*
  * The ROG Ally device presents multiple USB interfaces (keyboard, mouse, gamepad,
@@ -368,6 +396,7 @@ static const u8 ALLY_FORCE_FEEDBACK_OFF[] = {
  * ally_handheld structure to share state across these separate HID interfaces.
  */
 static void ally_resume_work_fn(struct work_struct *work);
+static void ally_x_ff_work_fn(struct work_struct *work);
 
 /*
  * Changes to ally_drvdata must lock: the raw_event callbacks, which may
@@ -383,6 +412,13 @@ static struct ally_handheld ally_drvdata = {
 	 */
 	.resume_work = __DELAYED_WORK_INITIALIZER(ally_drvdata.resume_work,
 						  ally_resume_work_fn, 0),
+	/*
+	 * Initialised statically for the same reason as resume_work: remove()
+	 * drains the work whichever of the interfaces probed or failed to
+	 * probe, so it must be safe to cancel unconditionally.
+	 */
+	.ff_work = __WORK_INITIALIZER(ally_drvdata.ff_work, ally_x_ff_work_fn),
+	.ff_lock = __SPIN_LOCK_UNLOCKED(ally_drvdata.ff_lock),
 };
 
 static const u8 asus_report_id_init[] = {
@@ -2519,6 +2555,86 @@ static bool ally_x_raw_event(struct input_dev *input, struct hid_device *hdev,
 	return true;
 }
 
+/**
+ * ally_x_send_ff_report() - Send a force-feedback report to the gamepad
+ * @ally: ally handheld structure
+ * @hdev: HID device
+ * @buf: buffer containing the report to send
+ * @len: length of the report
+ *
+ * The gamepad interface consumes force-feedback packets as output reports,
+ * unlike the config interface which expects feature reports: a rumble packet
+ * sent as HID_REQ_SET_REPORT would be rejected by the hardware.
+ *
+ * Return: count of data transferred, negative if error
+ */
+static int ally_x_send_ff_report(struct ally_handheld *ally,
+				 struct hid_device *hdev,
+				 const u8 *buf, size_t len)
+{
+	u8 *dmabuf __free(kfree) = kmemdup(buf, len, GFP_KERNEL);
+
+	if (!dmabuf)
+		return -ENOMEM;
+
+	scoped_guard(mutex, &ally->intf_mutex)
+		return hid_hw_output_report(hdev, dmabuf, len);
+}
+
+static int ally_x_send_ff_off(struct ally_handheld *ally, struct hid_device *hdev)
+{
+	return ally_x_send_ff_report(ally, hdev, ALLY_FORCE_FEEDBACK_OFF,
+				     sizeof(ALLY_FORCE_FEEDBACK_OFF));
+}
+
+static void ally_x_ff_work_fn(struct work_struct *work)
+{
+	struct ally_handheld *ally =
+		container_of(work, struct ally_handheld, ff_work);
+	struct hid_device *hdev = NULL;
+	struct ff_report report;
+	bool update = false;
+	int ret;
+
+	scoped_guard(spinlock_irqsave, &ally->ff_lock) {
+		if (ally->update_ff) {
+			report = ally->ff_packet;
+			ally->update_ff = false;
+			update = true;
+			hdev = ally->ally_x_hdev;
+		}
+	}
+
+	if (!update || !hdev)
+		return;
+
+	ret = ally_x_send_ff_report(ally, hdev, (u8 *)&report, sizeof(report));
+	if (ret < 0)
+		hid_err(hdev, "Failed to send force-feedback: %d\n", ret);
+}
+
+static int ally_x_play_effect(struct input_dev *idev, void *data,
+			     struct ff_effect *effect)
+{
+	struct ally_handheld *ally = &ally_drvdata;
+
+	if (effect->type != FF_RUMBLE)
+		return 0;
+
+	scoped_guard(spinlock_irqsave, &ally->ff_lock) {
+		ally->ff_packet.ff.magnitude_strong =
+			effect->u.rumble.strong_magnitude * ALLY_FF_MAX_INTENSITY / 65535;
+		ally->ff_packet.ff.magnitude_weak =
+			effect->u.rumble.weak_magnitude * ALLY_FF_MAX_INTENSITY / 65535;
+		ally->update_ff = true;
+
+		if (ally->ff_work_initialized)
+			schedule_work(&ally->ff_work);
+	}
+
+	return 0;
+}
+
 static struct input_dev *ally_x_alloc_input_dev(struct hid_device *hdev)
 {
 	struct input_dev *input_dev = devm_input_allocate_device(&hdev->dev);
@@ -2574,6 +2690,21 @@ static int ally_x_setup_input(struct hid_device *hdev, struct ally_handheld *all
 	input_set_capability(input, EV_KEY, BTN_TRIGGER_HAPPY);
 	input_set_capability(input, EV_KEY, BTN_TRIGGER_HAPPY1);
 
+	memcpy(&ally->ff_packet, ALLY_FORCE_FEEDBACK_OFF, sizeof(ally->ff_packet));
+	ally->ff_work_initialized = true;
+
+	input_set_capability(input, EV_FF, FF_RUMBLE);
+
+	/*
+	 * A registered device advertising FF_RUMBLE without the memless core
+	 * behind it would crash input_ff_upload(): fail the whole setup instead.
+	 */
+	ret = input_ff_create_memless(input, NULL, ally_x_play_effect);
+	if (ret) {
+		hid_err(hdev, "Failed to create force-feedback: %d\n", ret);
+		goto ally_x_setup_input_err;
+	}
+
 	ret = input_register_device(input);
 	if (ret) {
 		hid_err(hdev, "Failed to register Ally X gamepad device: %d\n", ret);
@@ -2592,13 +2723,28 @@ static int ally_x_setup_input(struct hid_device *hdev, struct ally_handheld *all
 
 static int hid_asus_ally_init(struct hid_device *hdev, struct ally_handheld *ally)
 {
-	int ret;
+	struct hid_device *x_hdev;
+	unsigned long flags;
 
-	/* Failure at this point is non-critical */
-	ret = ally_gamepad_send_packet(ally, hdev, ALLY_FORCE_FEEDBACK_OFF,
-				       sizeof(ALLY_FORCE_FEEDBACK_OFF));
-	if (ret < 0)
-		hid_err(hdev, "Ally failed to init force-feedback off: %d\n", ret);
+	/*
+	 * The force-feedback "off" packet belongs to the gamepad interface,
+	 * which consumes it as an output report: the config interface probed
+	 * here would reject it. The gamepad probe path sends the packet itself,
+	 * so this only matters when the gamepad interface is already bound,
+	 * e.g. after a reset resume that re-initialized the MCU.
+	 */
+	spin_lock_irqsave(&ally_data_lock, flags);
+	x_hdev = ally->ally_x_hdev;
+	spin_unlock_irqrestore(&ally_data_lock, flags);
+
+	if (x_hdev) {
+		/* Failure at this point is non-critical */
+		int ret = ally_x_send_ff_off(ally, x_hdev);
+
+		if (ret < 0)
+			hid_err(hdev, "Ally failed to init force-feedback off: %d\n",
+				ret);
+	}
 
 	return 0;
 }
@@ -2717,6 +2863,14 @@ static struct ally_handheld *hid_asus_ally_probe(struct hid_device *hdev)
 			return ERR_PTR(ret);
 		}
 
+		/*
+		 * Make sure rumble starts disabled: this is the interface that
+		 * owns the force-feedback output report. Failure is non-critical.
+		 */
+		ret = ally_x_send_ff_off(&ally_drvdata, hdev);
+		if (ret < 0)
+			hid_warn(hdev, "Failed to disable force-feedback: %d\n", ret);
+
 		spin_lock_irqsave(&ally_data_lock, flags);
 		ally_drvdata.ally_x_hdev = hdev;
 		spin_unlock_irqrestore(&ally_data_lock, flags);
@@ -2741,6 +2895,7 @@ static struct ally_handheld *hid_asus_ally_probe(struct hid_device *hdev)
 static void hid_asus_ally_remove(struct hid_device *hdev, struct ally_handheld *ally)
 {
 	unsigned long flags;
+	bool owns_xpad;
 
 	if (!ally)
 		return;
@@ -2754,7 +2909,36 @@ static void hid_asus_ally_remove(struct hid_device *hdev, struct ally_handheld *
 	cancel_delayed_work_sync(&ally->resume_work);
 
 	spin_lock_irqsave(&ally_data_lock, flags);
-	if (ally->ally_x_hdev == hdev) {
+	owns_xpad = ally->ally_x_hdev == hdev;
+	spin_unlock_irqrestore(&ally_data_lock, flags);
+
+	if (owns_xpad) {
+		/*
+		 * Stop queueing force-feedback work before the gamepad
+		 * pointers are cleared: play_effect() tests the flag under the
+		 * same lock, so no work can be queued past the cancel below.
+		 */
+		scoped_guard(spinlock_irqsave, &ally->ff_lock)
+			ally->ff_work_initialized = false;
+
+		/*
+		 * cancel_work_sync() may sleep: keep it out of ally_data_lock,
+		 * but run it before the pointers are cleared so in-flight work
+		 * cannot outlive the interface it sends through.
+		 */
+		cancel_work_sync(&ally->ff_work);
+
+		/*
+		 * The input core can no longer stop effects through the
+		 * disabled work: quiesce any rumble still playing ourselves,
+		 * or the device would keep vibrating after being unbound.
+		 */
+		if (ally_x_send_ff_off(ally, hdev) < 0)
+			hid_warn(hdev, "Failed to stop force-feedback\n");
+	}
+
+	spin_lock_irqsave(&ally_data_lock, flags);
+	if (owns_xpad) {
 		ally->ally_x_input = NULL;
 		ally->ally_x_hdev = NULL;
 	}
-- 
2.47.3