Merge patch series "Support system sleep with offloaded usb transfers" into usb-next

Guan-Yu Lin <guanyulin@google.com> says:

Wesley Cheng and Mathias Nyman's USB offload design enables a
co-processor to handle some USB transfers, potentially allowing the
system to sleep (suspend-to-RAM) and save power. However, Linux's System
Sleep model halts the USB host controller when the main system isn't
managing any USB transfers. To address this, the proposal modifies the
system to recognize offloaded USB transfers and manage power
accordingly. This way, offloaded USB transfers could still happen during
system sleep (Suspend-to-RAM).

This involves two key steps:
1. Transfer Status Tracking: Propose offload_usage and corresponding
   apis drivers could track USB transfers on the co-processor, ensuring
   the system is aware of any ongoing activity.
2. Power Management Adjustment:  Modifications to the USB driver stack
   (xhci host controller driver, and USB device drivers) allow the
   system to sleep (Suspend-to-RAM) without disrupting co-processor
   managed USB transfers. This involves adding conditional checks to
   bypass some power management operations in the System Sleep model.

Link: https://lore.kernel.org/r/20250911142051.90822-1-guanyulin@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

9 files changed, 284 insertions, 10 deletions

diff --git a/drivers/usb/core/Makefile b/drivers/usb/core/Makefile
index ac006abd13b3..766000b4939e 100644
--- a/drivers/usb/core/Makefile
+++ b/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
 
diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 25358cf3e324..6418cfb0fb37 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -1420,11 +1420,28 @@ static int usb_suspend_both(struct usb_device *udev, pm_message_t msg)
 			udev->state == USB_STATE_SUSPENDED)
 		goto done;
 
+	if (msg.event == PM_EVENT_SUSPEND && usb_offload_check(udev)) {
+		dev_dbg(&udev->dev, "device offloaded, skip suspend.\n");
+		udev->offload_at_suspend = 1;
+	}
+
 	/* Suspend all the interfaces and then udev itself */
 	if (udev->actconfig) {
 		n = udev->actconfig->desc.bNumInterfaces;
 		for (i = n - 1; i >= 0; --i) {
 			intf = udev->actconfig->interface[i];
+			/*
+			 * Don't suspend interfaces with remote wakeup while
+			 * the controller is active. This preserves pending
+			 * interrupt urbs, allowing interrupt events to be
+			 * handled during system suspend.
+			 */
+			if (udev->offload_at_suspend &&
+			    intf->needs_remote_wakeup) {
+				dev_dbg(&intf->dev,
+					"device offloaded, skip suspend.\n");
+				continue;
+			}
 			status = usb_suspend_interface(udev, intf, msg);
 
 			/* Ignore errors during system sleep transitions */
@@ -1435,7 +1452,8 @@ static int usb_suspend_both(struct usb_device *udev, pm_message_t msg)
 		}
 	}
 	if (status == 0) {
-		status = usb_suspend_device(udev, msg);
+		if (!udev->offload_at_suspend)
+			status = usb_suspend_device(udev, msg);
 
 		/*
 		 * Ignore errors from non-root-hub devices during
@@ -1480,9 +1498,11 @@ static int usb_suspend_both(struct usb_device *udev, pm_message_t msg)
 	 */
 	} else {
 		udev->can_submit = 0;
-		for (i = 0; i < 16; ++i) {
-			usb_hcd_flush_endpoint(udev, udev->ep_out[i]);
-			usb_hcd_flush_endpoint(udev, udev->ep_in[i]);
+		if (!udev->offload_at_suspend) {
+			for (i = 0; i < 16; ++i) {
+				usb_hcd_flush_endpoint(udev, udev->ep_out[i]);
+				usb_hcd_flush_endpoint(udev, udev->ep_in[i]);
+			}
 		}
 	}
 
@@ -1524,17 +1544,35 @@ static int usb_resume_both(struct usb_device *udev, pm_message_t msg)
 	udev->can_submit = 1;
 
 	/* Resume the device */
-	if (udev->state == USB_STATE_SUSPENDED || udev->reset_resume)
-		status = usb_resume_device(udev, msg);
+	if (udev->state == USB_STATE_SUSPENDED || udev->reset_resume) {
+		if (!udev->offload_at_suspend)
+			status = usb_resume_device(udev, msg);
+		else
+			dev_dbg(&udev->dev,
+				"device offloaded, skip resume.\n");
+	}
 
 	/* Resume the interfaces */
 	if (status == 0 && udev->actconfig) {
 		for (i = 0; i < udev->actconfig->desc.bNumInterfaces; i++) {
 			intf = udev->actconfig->interface[i];
+			/*
+			 * Interfaces with remote wakeup aren't suspended
+			 * while the controller is active. This preserves
+			 * pending interrupt urbs, allowing interrupt events
+			 * to be handled during system suspend.
+			 */
+			if (udev->offload_at_suspend &&
+			    intf->needs_remote_wakeup) {
+				dev_dbg(&intf->dev,
+					"device offloaded, skip resume.\n");
+				continue;
+			}
 			usb_resume_interface(udev, intf, msg,
 					udev->reset_resume);
 		}
 	}
+	udev->offload_at_suspend = 0;
 	usb_mark_last_busy(udev);
 
  done:
diff --git a/drivers/usb/core/offload.c b/drivers/usb/core/offload.c
new file mode 100644
index 000000000000..7c699f1b8d2b
--- /dev/null
+++ b/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);
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
index b88b6271cb30..b6b0b8489523 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/xhci-plat.c b/drivers/usb/host/xhci-plat.c
index 5eb51797de32..3a56d8f94519 100644
--- a/drivers/usb/host/xhci-plat.c
+++ b/drivers/usb/host/xhci-plat.c
@@ -20,6 +20,7 @@
 #include <linux/acpi.h>
 #include <linux/usb/of.h>
 #include <linux/reset.h>
+#include <linux/usb/xhci-sideband.h>
 
 #include "xhci.h"
 #include "xhci-plat.h"
@@ -454,7 +455,7 @@ void xhci_plat_remove(struct platform_device *dev)
 }
 EXPORT_SYMBOL_GPL(xhci_plat_remove);
 
-static int xhci_plat_suspend(struct device *dev)
+static int xhci_plat_suspend_common(struct device *dev)
 {
 	struct usb_hcd	*hcd = dev_get_drvdata(dev);
 	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
@@ -482,6 +483,25 @@ static int xhci_plat_suspend(struct device *dev)
 	return 0;
 }
 
+static int xhci_plat_suspend(struct device *dev)
+{
+	struct usb_hcd	*hcd = dev_get_drvdata(dev);
+	struct xhci_plat_priv *priv = hcd_to_xhci_priv(hcd);
+
+	if (xhci_sideband_check(hcd)) {
+		priv->sideband_at_suspend = 1;
+		dev_dbg(dev, "sideband instance active, skip suspend.\n");
+		return 0;
+	}
+
+	return xhci_plat_suspend_common(dev);
+}
+
+static int xhci_plat_freeze(struct device *dev)
+{
+	return xhci_plat_suspend_common(dev);
+}
+
 static int xhci_plat_resume_common(struct device *dev, bool power_lost)
 {
 	struct usb_hcd	*hcd = dev_get_drvdata(dev);
@@ -526,6 +546,20 @@ disable_clks:
 
 static int xhci_plat_resume(struct device *dev)
 {
+	struct usb_hcd	*hcd = dev_get_drvdata(dev);
+	struct xhci_plat_priv *priv = hcd_to_xhci_priv(hcd);
+
+	if (priv->sideband_at_suspend) {
+		priv->sideband_at_suspend = 0;
+		dev_dbg(dev, "sideband instance active, skip resume.\n");
+		return 0;
+	}
+
+	return xhci_plat_resume_common(dev, false);
+}
+
+static int xhci_plat_thaw(struct device *dev)
+{
 	return xhci_plat_resume_common(dev, false);
 }
 
@@ -558,9 +592,9 @@ static int __maybe_unused xhci_plat_runtime_resume(struct device *dev)
 const struct dev_pm_ops xhci_plat_pm_ops = {
 	.suspend = pm_sleep_ptr(xhci_plat_suspend),
 	.resume = pm_sleep_ptr(xhci_plat_resume),
-	.freeze = pm_sleep_ptr(xhci_plat_suspend),
-	.thaw = pm_sleep_ptr(xhci_plat_resume),
-	.poweroff = pm_sleep_ptr(xhci_plat_suspend),
+	.freeze = pm_sleep_ptr(xhci_plat_freeze),
+	.thaw = pm_sleep_ptr(xhci_plat_thaw),
+	.poweroff = pm_sleep_ptr(xhci_plat_freeze),
 	.restore = pm_sleep_ptr(xhci_plat_restore),
 
 	SET_RUNTIME_PM_OPS(xhci_plat_runtime_suspend,
diff --git a/drivers/usb/host/xhci-plat.h b/drivers/usb/host/xhci-plat.h
index fe4f95e690fa..2b32a93d2b76 100644
--- a/drivers/usb/host/xhci-plat.h
+++ b/drivers/usb/host/xhci-plat.h
@@ -16,6 +16,7 @@ struct xhci_plat_priv {
 	const char *firmware_name;
 	unsigned long long quirks;
 	bool power_lost;
+	unsigned sideband_at_suspend:1;
 	void (*plat_start)(struct usb_hcd *);
 	int (*init_quirk)(struct usb_hcd *);
 	int (*suspend_quirk)(struct usb_hcd *);
diff --git a/drivers/usb/host/xhci-sideband.c b/drivers/usb/host/xhci-sideband.c
index d49f9886dd84..e771a476fef2 100644
--- a/drivers/usb/host/xhci-sideband.c
+++ b/drivers/usb/host/xhci-sideband.c
@@ -267,6 +267,31 @@ xhci_sideband_get_event_buffer(struct xhci_sideband *sb)
 EXPORT_SYMBOL_GPL(xhci_sideband_get_event_buffer);
 
 /**
+ * xhci_sideband_check - check the existence of active sidebands
+ * @hcd: the host controller driver associated with the target host controller
+ *
+ * Allow other drivers, such as usb controller driver, to check if there are
+ * any sideband activity on the host controller. This information could be used
+ * for power management or other forms of resource management. 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 active sideband existence, false otherwise.
+ */
+bool xhci_sideband_check(struct usb_hcd *hcd)
+{
+	struct usb_device *udev = hcd->self.root_hub;
+	bool active;
+
+	usb_lock_device(udev);
+	active = usb_offload_check(udev);
+	usb_unlock_device(udev);
+
+	return active;
+}
+EXPORT_SYMBOL_GPL(xhci_sideband_check);
+
+/**
  * xhci_sideband_create_interrupter - creates a new interrupter for this sideband
  * @sb: sideband instance for this usb device
  * @num_seg: number of event ring segments to allocate
@@ -286,6 +311,7 @@ xhci_sideband_create_interrupter(struct xhci_sideband *sb, int num_seg,
 				 bool ip_autoclear, u32 imod_interval, int intr_num)
 {
 	int ret = 0;
+	struct usb_device *udev;
 
 	if (!sb || !sb->xhci)
 		return -ENODEV;
@@ -304,6 +330,9 @@ xhci_sideband_create_interrupter(struct xhci_sideband *sb, int num_seg,
 		goto out;
 	}
 
+	udev = sb->vdev->udev;
+	ret = usb_offload_get(udev);
+
 	sb->ir->ip_autoclear = ip_autoclear;
 
 out:
@@ -323,6 +352,8 @@ EXPORT_SYMBOL_GPL(xhci_sideband_create_interrupter);
 void
 xhci_sideband_remove_interrupter(struct xhci_sideband *sb)
 {
+	struct usb_device *udev;
+
 	if (!sb || !sb->ir)
 		return;
 
@@ -330,6 +361,11 @@ xhci_sideband_remove_interrupter(struct xhci_sideband *sb)
 	xhci_remove_secondary_interrupter(xhci_to_hcd(sb->xhci), sb->ir);
 
 	sb->ir = NULL;
+	udev = sb->vdev->udev;
+
+	if (udev->state != USB_STATE_NOTATTACHED)
+		usb_offload_put(udev);
+
 	mutex_unlock(&sb->mutex);
 }
 EXPORT_SYMBOL_GPL(xhci_sideband_remove_interrupter);
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 70ef00c42d22..e85105939af8 100644
--- a/include/linux/usb.h
+++ b/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. */
diff --git a/include/linux/usb/xhci-sideband.h b/include/linux/usb/xhci-sideband.h
index 45288c392f6e..005257085dcb 100644
--- a/include/linux/usb/xhci-sideband.h
+++ b/include/linux/usb/xhci-sideband.h
@@ -11,6 +11,7 @@
 
 #include <linux/scatterlist.h>
 #include <linux/usb.h>
+#include <linux/usb/hcd.h>
 
 #define	EP_CTX_PER_DEV		31	/* FIXME defined twice, from xhci.h */
 
@@ -83,6 +84,14 @@ xhci_sideband_get_endpoint_buffer(struct xhci_sideband *sb,
 				  struct usb_host_endpoint *host_ep);
 struct sg_table *
 xhci_sideband_get_event_buffer(struct xhci_sideband *sb);
+
+#if IS_ENABLED(CONFIG_USB_XHCI_SIDEBAND)
+bool xhci_sideband_check(struct usb_hcd *hcd);
+#else
+static inline bool xhci_sideband_check(struct usb_hcd *hcd)
+{ return false; }
+#endif /* IS_ENABLED(CONFIG_USB_XHCI_SIDEBAND) */
+
 int
 xhci_sideband_create_interrupter(struct xhci_sideband *sb, int num_seg,
 				 bool ip_autoclear, u32 imod_interval, int intr_num);