usb: offload: add apis for offload usage tracking

Introduce offload_usage and corresponding apis to track offload usage
on each USB device. Offload denotes that there is another co-processor
accessing the USB device via the same USB host controller. To optimize
power usage, it's essential to monitor whether the USB device is
actively used by other co-processor. This information is vital when
determining if a USB device can be safely suspended during system power
state transitions.

Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
Link: https://lore.kernel.org/r/20250911142051.90822-3-guanyulin@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250911142051.90822-3-guanyulin@google.com

drivers/usb/core/Makefile

@@ -9,6 +9,7 @@ usbcore-y += devio.o notify.o generic.o quirks.o devices.o
 usbcore-y += phy.o port.o
 
 usbcore-$(CONFIG_OF)		+= of.o
+usbcore-$(CONFIG_USB_XHCI_SIDEBAND)	+= offload.o
 usbcore-$(CONFIG_USB_PCI)		+= hcd-pci.o
 usbcore-$(CONFIG_ACPI)		+= usb-acpi.o
 

drivers/usb/core/offload.c

@@ -0,0 +1,136 @@
+// 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;
+
+	usb_lock_device(udev);
+	if (udev->state == USB_STATE_NOTATTACHED) {
+		usb_unlock_device(udev);
+		return -ENODEV;
+	}
+
+	if (udev->state == USB_STATE_SUSPENDED ||
+		   udev->offload_at_suspend) {
+		usb_unlock_device(udev);
+		return -EBUSY;
+	}
+
+	/*
+	 * offload_usage could only be modified when the device is active, since
+	 * it will alter the suspend flow of the device.
+	 */
+	ret = usb_autoresume_device(udev);
+	if (ret < 0) {
+		usb_unlock_device(udev);
+		return ret;
+	}
+
+	udev->offload_usage++;
+	usb_autosuspend_device(udev);
+	usb_unlock_device(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;
+
+	usb_lock_device(udev);
+	if (udev->state == USB_STATE_NOTATTACHED) {
+		usb_unlock_device(udev);
+		return -ENODEV;
+	}
+
+	if (udev->state == USB_STATE_SUSPENDED ||
+		   udev->offload_at_suspend) {
+		usb_unlock_device(udev);
+		return -EBUSY;
+	}
+
+	/*
+	 * offload_usage could only be modified when the device is active, since
+	 * it will alter the suspend flow of the device.
+	 */
+	ret = usb_autoresume_device(udev);
+	if (ret < 0) {
+		usb_unlock_device(udev);
+		return ret;
+	}
+
+	/* Drop the count when it wasn't 0, ignore the operation otherwise. */
+	if (udev->offload_usage)
+		udev->offload_usage--;
+	usb_autosuspend_device(udev);
+	usb_unlock_device(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 downstream usb devices are all either suspended or marked as
+ * "offload_at_suspend" 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;
+	int port1;
+
+	usb_hub_for_each_child(udev, port1, child) {
+		usb_lock_device(child);
+		active = usb_offload_check(child);
+		usb_unlock_device(child);
+		if (active)
+			return true;
+	}
+
+	return !!udev->offload_usage;
+}
+EXPORT_SYMBOL_GPL(usb_offload_check);

drivers/usb/core/usb.c

@@ -670,6 +670,7 @@ struct usb_device *usb_alloc_dev(struct usb_device *parent,
 	set_dev_node(&dev->dev, dev_to_node(bus->sysdev));
 	dev->state = USB_STATE_ATTACHED;
 	dev->lpm_disable_count = 1;
+	dev->offload_usage = 0;
 	atomic_set(&dev->urbnum, 0);
 
 	INIT_LIST_HEAD(&dev->ep0.urb_list);

include/linux/usb.h

@@ -636,6 +636,8 @@ struct usb3_lpm_parameters {
  * @do_remote_wakeup:  remote wakeup should be enabled
  * @reset_resume: needs reset instead of resume
  * @port_is_suspended: the upstream port is suspended (L2 or U3)
+ * @offload_at_suspend: offload activities during suspend is enabled.
+ * @offload_usage: number of offload activities happening on this usb device.
  * @slot_id: Slot ID assigned by xHCI
  * @l1_params: best effor service latency for USB2 L1 LPM state, and L1 timeout.
  * @u1_params: exit latencies for USB3 U1 LPM state, and hub-initiated timeout.
@@ -724,6 +726,8 @@ struct usb_device {
 	unsigned do_remote_wakeup:1;
 	unsigned reset_resume:1;
 	unsigned port_is_suspended:1;
+	unsigned offload_at_suspend:1;
+	int offload_usage;
 	enum usb_link_tunnel_mode tunnel_mode;
 	struct device_link *usb4_link;
 
@@ -841,6 +845,20 @@ static inline void usb_mark_last_busy(struct usb_device *udev)
 { }
 #endif
 
+#if IS_ENABLED(CONFIG_USB_XHCI_SIDEBAND)
+int usb_offload_get(struct usb_device *udev);
+int usb_offload_put(struct usb_device *udev);
+bool usb_offload_check(struct usb_device *udev);
+#else
+
+static inline int usb_offload_get(struct usb_device *udev)
+{ return 0; }
+static inline int usb_offload_put(struct usb_device *udev)
+{ return 0; }
+static inline bool usb_offload_check(struct usb_device *udev)
+{ return false; }
+#endif
+
 extern int usb_disable_lpm(struct usb_device *udev);
 extern void usb_enable_lpm(struct usb_device *udev);
 /* Same as above, but these functions lock/unlock the bandwidth_mutex. */