1 files changed, 152 insertions, 0 deletions

diff --git a/drivers/usb/core/offload.c b/drivers/usb/core/offload.c
new file mode 100644
index 000000000000..9db3cfedd29c
--- /dev/null
+++ b/drivers/usb/core/offload.c
@@ -0,0 +1,152 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * offload.c - USB offload related functions
+ *
+ * Copyright (c) 2025, Google LLC.
+ *
+ * Author: Guan-Yu Lin
+ */
+
+#include <linux/usb.h>
+
+#include "usb.h"
+
+/**
+ * usb_offload_get - increment the offload_usage of a USB device
+ * @udev: the USB device to increment its offload_usage
+ *
+ * Incrementing the offload_usage of a usb_device indicates that offload is
+ * enabled on this usb_device; that is, another entity is actively handling USB
+ * transfers. This information allows the USB driver to adjust its power
+ * management policy based on offload activity.
+ *
+ * Return: 0 on success. A negative error code otherwise.
+ */
+int usb_offload_get(struct usb_device *udev)
+{
+	int ret = 0;
+
+	if (!usb_get_dev(udev))
+		return -ENODEV;
+
+	if (pm_runtime_get_if_active(&udev->dev) != 1) {
+		ret = -EBUSY;
+		goto err_rpm;
+	}
+
+	spin_lock(&udev->offload_lock);
+
+	if (udev->offload_pm_locked) {
+		ret = -EAGAIN;
+		goto err;
+	}
+
+	udev->offload_usage++;
+
+err:
+	spin_unlock(&udev->offload_lock);
+	pm_runtime_put_autosuspend(&udev->dev);
+err_rpm:
+	usb_put_dev(udev);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(usb_offload_get);
+
+/**
+ * usb_offload_put - drop the offload_usage of a USB device
+ * @udev: the USB device to drop its offload_usage
+ *
+ * The inverse operation of usb_offload_get, which drops the offload_usage of
+ * a USB device. This information allows the USB driver to adjust its power
+ * management policy based on offload activity.
+ *
+ * Return: 0 on success. A negative error code otherwise.
+ */
+int usb_offload_put(struct usb_device *udev)
+{
+	int ret = 0;
+
+	if (!usb_get_dev(udev))
+		return -ENODEV;
+
+	if (pm_runtime_get_if_active(&udev->dev) != 1) {
+		ret = -EBUSY;
+		goto err_rpm;
+	}
+
+	spin_lock(&udev->offload_lock);
+
+	if (udev->offload_pm_locked) {
+		ret = -EAGAIN;
+		goto err;
+	}
+
+	/* Drop the count when it wasn't 0, ignore the operation otherwise. */
+	if (udev->offload_usage)
+		udev->offload_usage--;
+
+err:
+	spin_unlock(&udev->offload_lock);
+	pm_runtime_put_autosuspend(&udev->dev);
+err_rpm:
+	usb_put_dev(udev);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(usb_offload_put);
+
+/**
+ * usb_offload_check - check offload activities on a USB device
+ * @udev: the USB device to check its offload activity.
+ *
+ * Check if there are any offload activity on the USB device right now. This
+ * information could be used for power management or other forms of resource
+ * management.
+ *
+ * The caller must hold @udev's device lock. In addition, the caller should
+ * ensure the device itself and the downstream usb devices are all marked as
+ * "offload_pm_locked" to ensure the correctness of the return value.
+ *
+ * Returns true on any offload activity, false otherwise.
+ */
+bool usb_offload_check(struct usb_device *udev) __must_hold(&udev->dev->mutex)
+{
+	struct usb_device *child;
+	bool active = false;
+	int port1;
+
+	if (udev->offload_usage)
+		return true;
+
+	usb_hub_for_each_child(udev, port1, child) {
+		usb_lock_device(child);
+		active = usb_offload_check(child);
+		usb_unlock_device(child);
+
+		if (active)
+			break;
+	}
+
+	return active;
+}
+EXPORT_SYMBOL_GPL(usb_offload_check);
+
+/**
+ * usb_offload_set_pm_locked - set the PM lock state of a USB device
+ * @udev: the USB device to modify
+ * @locked: the new lock state
+ *
+ * Setting @locked to true prevents offload_usage from being modified. This
+ * ensures that offload activities cannot be started or stopped during critical
+ * power management transitions, maintaining a stable state for the duration
+ * of the transition.
+ */
+void usb_offload_set_pm_locked(struct usb_device *udev, bool locked)
+{
+	spin_lock(&udev->offload_lock);
+	udev->offload_pm_locked = locked;
+	spin_unlock(&udev->offload_lock);
+}
+EXPORT_SYMBOL_GPL(usb_offload_set_pm_locked);