[PATCH v13 2/4] usb: add apis for offload usage tracking

Guan-Yu Lin
2025-05-28T09:09:14Z

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>
---
drivers/usb/core/driver.c | 125 ++++++++++++++++++++++++++++++++++++++
drivers/usb/core/usb.c | 1 +
drivers/usb/host/Kconfig | 11 ++++
include/linux/usb.h | 18 ++++++
4 files changed, 155 insertions(+)

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 460d4dde5994..0690619454fe 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -2036,6 +2036,131 @@ int usb_disable_usb2_hardware_lpm(struct usb_device *udev)

#endif /* CONFIG_PM */

+#if IS_ENABLED(CONFIG_USB_XHCI_SIDEBAND_SUSPEND)
+
+/**
+ * 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) {
+ ret = -ENODEV;
+ goto unlock_device;
+ } else if (udev->state == USB_STATE_SUSPENDED ||
+ udev->offload_at_suspend) {
+ ret = -EBUSY;
+ goto unlock_device;
+ }
+
+ /*
+ * 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)
+ goto unlock_device;
+
+ udev->offload_usage++;
+ usb_autosuspend_device(udev);
+
+unlock_device:
+ 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) {
+ ret = -ENODEV;
+ goto unlock_device;
+ } else if (udev->state == USB_STATE_SUSPENDED ||
+ udev->offload_at_suspend) {
+ ret = -EBUSY;
+ goto unlock_device;
+ }
+
+ /*
+ * 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)
+ goto unlock_device;
+
+ /* Drop the count when it wasn't 0, ignore the operation otherwise. */
+ if (udev->offload_usage)
+ udev->offload_usage--;
+ usb_autosuspend_device(udev);
+
+unlock_device:
+ 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)
+{
+ 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);
+
+#endif /* IS_ENABLED(CONFIG_USB_XHCI_SIDEBAND_SUSPEND) */
+
const struct bus_type usb_bus_type = {
.name = "usb",
.match = usb_device_match,
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
index 118fa4c93a79..43efd9d939c0 100644
--- a/drivers/usb/core/usb.c
+++ b/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);
diff --git a/drivers/usb/host/Kconfig b/drivers/usb/host/Kconfig
index 109100cc77a3..49b9cdc11298 100644
--- a/drivers/usb/host/Kconfig
+++ b/drivers/usb/host/Kconfig
@@ -113,6 +113,17 @@ config USB_XHCI_SIDEBAND
xHCI USB endpoints directly, allowing CPU to sleep while playing
audio.

+config USB_XHCI_SIDEBAND_SUSPEND
+ bool "xHCI support for sideband during system suspend"
+ depends on USB_XHCI_SIDEBAND
+ depends on USB_XHCI_PLATFORM
+ depends on SUSPEND
+ help
+ Say 'Y' to enable the support for the xHCI sideband capability
+ after system suspended. In addition to USB_XHCI_SIDEBAND, this
+ config allows endpoints and interrupters associated with the
+ sideband function when system is suspended.
+
config USB_XHCI_TEGRA
tristate "xHCI support for NVIDIA Tegra SoCs"
depends on PHY_TEGRA_XUSB
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 1b2545b4363b..f5bca317fa4c 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -635,6 +635,8 @@ 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.
@@ -723,6 +725,8 @@ 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;

int slot_id;
@@ -839,6 +843,20 @@ static inline void usb_mark_last_busy(struct usb_device *udev)
{ }
#endif

+#if IS_ENABLED(CONFIG_USB_XHCI_SIDEBAND_SUSPEND)
+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. */
--
2.49.0.1164.gab81da1b16-goog