[PATCH v7 0/5] Support system sleep with offloaded usb transfers

[PATCH v7 0/5] Support system sleep with offloaded usb transfers

[Guan-Yu Lin]

Wesley Cheng and Mathias Nyman's USB offload design enables a co-processor
to handle some USB transfers, potentially allowing the main system to
sleep and save power. However, Linux's power management system 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 involves two key steps:
1. Transfer Status Tracking: Propose xhci_sideband_get and
xhci_sideband_put to 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
(dwc3 controller driver, xhci host controller driver, and USB device
drivers) allow the system to sleep without disrupting co-processor managed
USB transfers. This involves adding conditional checks to bypass some
power management operations.

patches depends on series "Introduce QC USB SND audio offloading support" 
https://lore.kernel.org/lkml/20241213235403.4109199-1-quic_wcheng@quicinc.com/T/

changelog
----------
Changes in v7:
- Remove counting mechanism in struct usb_hcd. The USB device's offload
  status will be solely recorded in each related struct usb_device.
- Utilizes `needs_remote_wakeup` attribute in struct usb_interface to
  control the suspend flow of USB interfaces and associated USB endpoints.
  This addresses the need to support interrupt transfers generated by
  offloaded USB devices while the system is suspended.
- Block any offload_usage change during USB device suspend period.

Changes in v6:
- Fix build errors when CONFIG_USB_XHCI_SIDEBAND is disabled.
- Explicitly specify the data structure of the drvdata refereced in
  dwc3_suspend(), dwc3_resume().
- Move the initialization of counters to the patches introducing them.

Changes in v5:
- Walk through the USB children in usb_sideband_check() to determine the
  sideband activity under the specific USB device. 
- Replace atomic_t by refcount_t.
- Reduce logs by using dev_dbg & remove __func__.

Changes in v4:
- Isolate the feature into USB driver stack.
- Integrate with series "Introduce QC USB SND audio offloading support"

Changes in v3:
- Integrate the feature with the pm core framework.

Changes in v2:
- Cosmetics changes on coding style.

[v3] PM / core: conditionally skip system pm in device/driver model
[v2] usb: host: enable suspend-to-RAM control in userspace
[v1] [RFC] usb: host: Allow userspace to control usb suspend flows
---

Guan-Yu Lin (5):
  usb: dwc3: separate dev_pm_ops for each pm_event
  usb: xhci-plat: separate dev_pm_ops for each pm_event
  usb: add apis for offload usage tracking
  xhci: sideband: add api to trace sideband usage
  usb: host: enable USB offload during system sleep

 drivers/usb/core/driver.c         | 145 ++++++++++++++++++++++++++++--
 drivers/usb/core/endpoint.c       |   8 --
 drivers/usb/core/usb.c            |   4 +
 drivers/usb/dwc3/core.c           | 105 +++++++++++++++++++++-
 drivers/usb/dwc3/core.h           |   1 +
 drivers/usb/host/xhci-plat.c      |  42 ++++++++-
 drivers/usb/host/xhci-sideband.c  |  82 +++++++++++++++++
 include/linux/usb.h               |  27 +++++-
 include/linux/usb/hcd.h           |   7 ++
 include/linux/usb/xhci-sideband.h |   6 ++
 sound/usb/qcom/qc_audio_offload.c |   3 +
 11 files changed, 410 insertions(+), 20 deletions(-)

-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v7 1/5] usb: dwc3: separate dev_pm_ops for each pm_event

[Guan-Yu Lin]

Separate dev_pm_ops for different power events such as suspend, thaw,
and hibernation. This is crucial when dwc3 driver needs to adapt its
behavior based on different power state changes.

Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
---
 drivers/usb/dwc3/core.c | 77 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 76 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 6c960ff30c92..0735881d4650 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -2632,6 +2632,76 @@ static int dwc3_resume(struct device *dev)
 	return ret;
 }
 
+static int dwc3_freeze(struct device *dev)
+{
+	struct dwc3	*dwc = dev_get_drvdata(dev);
+	int		ret;
+
+	ret = dwc3_suspend_common(dwc, PMSG_FREEZE);
+	if (ret)
+		return ret;
+
+	pinctrl_pm_select_sleep_state(dev);
+
+	return 0;
+}
+
+static int dwc3_thaw(struct device *dev)
+{
+	struct dwc3	*dwc = dev_get_drvdata(dev);
+	int		ret;
+
+	pinctrl_pm_select_default_state(dev);
+
+	pm_runtime_disable(dev);
+	pm_runtime_set_active(dev);
+
+	ret = dwc3_resume_common(dwc, PMSG_THAW);
+	if (ret) {
+		pm_runtime_set_suspended(dev);
+		return ret;
+	}
+
+	pm_runtime_enable(dev);
+
+	return 0;
+}
+
+static int dwc3_poweroff(struct device *dev)
+{
+	struct dwc3	*dwc = dev_get_drvdata(dev);
+	int		ret;
+
+	ret = dwc3_suspend_common(dwc, PMSG_HIBERNATE);
+	if (ret)
+		return ret;
+
+	pinctrl_pm_select_sleep_state(dev);
+
+	return 0;
+}
+
+static int dwc3_restore(struct device *dev)
+{
+	struct dwc3	*dwc = dev_get_drvdata(dev);
+	int		ret;
+
+	pinctrl_pm_select_default_state(dev);
+
+	pm_runtime_disable(dev);
+	pm_runtime_set_active(dev);
+
+	ret = dwc3_resume_common(dwc, PMSG_RESTORE);
+	if (ret) {
+		pm_runtime_set_suspended(dev);
+		return ret;
+	}
+
+	pm_runtime_enable(dev);
+
+	return 0;
+}
+
 static void dwc3_complete(struct device *dev)
 {
 	struct dwc3	*dwc = dev_get_drvdata(dev);
@@ -2649,7 +2719,12 @@ static void dwc3_complete(struct device *dev)
 #endif /* CONFIG_PM_SLEEP */
 
 static const struct dev_pm_ops dwc3_dev_pm_ops = {
-	SET_SYSTEM_SLEEP_PM_OPS(dwc3_suspend, dwc3_resume)
+	.suspend = pm_sleep_ptr(dwc3_suspend),
+	.resume = pm_sleep_ptr(dwc3_resume),
+	.freeze = pm_sleep_ptr(dwc3_freeze),
+	.thaw = pm_sleep_ptr(dwc3_thaw),
+	.poweroff = pm_sleep_ptr(dwc3_poweroff),
+	.restore = pm_sleep_ptr(dwc3_restore),
 	.complete = dwc3_complete,
 
 	/*
-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v7 2/5] usb: xhci-plat: separate dev_pm_ops for each pm_event

[Guan-Yu Lin]

Separate dev_pm_ops for different power events such as suspend, thaw,
and hibernation. This is crucial when xhci-plat driver needs to adapt
its behavior based on different power state changes.

Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
---
 drivers/usb/host/xhci-plat.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
index 3acdbbd9aea3..b676d4dbcec1 100644
--- a/drivers/usb/host/xhci-plat.c
+++ b/drivers/usb/host/xhci-plat.c
@@ -450,7 +450,7 @@ 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 pm_message pmsg)
 {
 	struct usb_hcd	*hcd = dev_get_drvdata(dev);
 	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
@@ -478,6 +478,21 @@ static int xhci_plat_suspend(struct device *dev)
 	return 0;
 }
 
+static int xhci_plat_suspend(struct device *dev)
+{
+	return xhci_plat_suspend_common(dev, PMSG_SUSPEND);
+}
+
+static int xhci_plat_freeze(struct device *dev)
+{
+	return xhci_plat_suspend_common(dev, PMSG_FREEZE);
+}
+
+static int xhci_plat_poweroff(struct device *dev)
+{
+	return xhci_plat_suspend_common(dev, PMSG_HIBERNATE);
+}
+
 static int xhci_plat_resume_common(struct device *dev, struct pm_message pmsg)
 {
 	struct usb_hcd	*hcd = dev_get_drvdata(dev);
@@ -524,6 +539,11 @@ static int xhci_plat_resume(struct device *dev)
 	return xhci_plat_resume_common(dev, PMSG_RESUME);
 }
 
+static int xhci_plat_thaw(struct device *dev)
+{
+	return xhci_plat_resume_common(dev, PMSG_THAW);
+}
+
 static int xhci_plat_restore(struct device *dev)
 {
 	return xhci_plat_resume_common(dev, PMSG_RESTORE);
@@ -553,9 +573,9 @@ 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_poweroff),
 	.restore = pm_sleep_ptr(xhci_plat_restore),
 
 	SET_RUNTIME_PM_OPS(xhci_plat_runtime_suspend,
-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v7 3/5] usb: add apis for offload usage tracking

[Guan-Yu Lin]

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 | 108 ++++++++++++++++++++++++++++++++++++++
 drivers/usb/core/usb.c    |   4 ++
 include/linux/usb.h       |  19 +++++++
 3 files changed, 131 insertions(+)

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index f203fdbfb6f6..01f6287cf73f 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -2037,6 +2037,114 @@ int usb_disable_usb2_hardware_lpm(struct usb_device *udev)
 
 #endif /* CONFIG_PM */
 
+#ifdef CONFIG_USB_XHCI_SIDEBAND
+
+/**
+ * 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.
+ *
+ * The caller must hold @udev's device lock.
+ *
+ * Return: 0 on success. A negative error code otherwise.
+ */
+int usb_offload_get(struct usb_device *udev)
+{
+	int ret;
+
+	if (udev->state == USB_STATE_NOTATTACHED ||
+			udev->state == USB_STATE_SUSPENDED)
+		return -EAGAIN;
+
+	/*
+	 * offload_usage could only be modified when the device is active, since
+	 * it will alter the suspend flow of the device.
+	 */
+	ret = pm_runtime_get_sync(&udev->dev);
+
+	if (ret < 0)
+		return ret;
+
+	refcount_inc(&udev->offload_usage);
+	pm_runtime_put_sync(&udev->dev);
+
+	return 0;
+}
+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.
+ *
+ * The caller must hold @udev's device lock.
+ *
+ * Return: 0 on success. A negative error code otherwise.
+ */
+int usb_offload_put(struct usb_device *udev)
+{
+	int ret;
+
+	if (udev->state == USB_STATE_NOTATTACHED ||
+			udev->state == USB_STATE_SUSPENDED)
+		return -EAGAIN;
+
+	/*
+	 * offload_usage could only be modified when the device is active, since
+	 * it will alter the suspend flow of the device.
+	 */
+	ret = pm_runtime_get_sync(&udev->dev);
+
+	if (ret < 0)
+		return ret;
+
+	/* Drop the count when it wasn't 0, ignore the operation otherwise. */
+	ret = refcount_add_not_zero(-1, &udev->offload_usage);
+	pm_runtime_put_sync(&udev->dev);
+
+	return 0;
+}
+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.
+ *
+ * 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) {
+		device_lock(&child->dev);
+		active = usb_offload_check(child);
+		device_unlock(&child->dev);
+		if (active)
+			return true;
+	}
+
+	return !!refcount_read(&udev->offload_usage);
+}
+EXPORT_SYMBOL_GPL(usb_offload_check);
+
+#endif /* CONFIG_USB_XHCI_SIDEBAND */
+
 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 0b4685aad2d5..888ab599fd06 100644
--- a/drivers/usb/core/usb.c
+++ b/drivers/usb/core/usb.c
@@ -672,6 +672,10 @@ struct usb_device *usb_alloc_dev(struct usb_device *parent,
 	dev->lpm_disable_count = 1;
 	atomic_set(&dev->urbnum, 0);
 
+#ifdef CONFIG_USB_XHCI_SIDEBAND
+	refcount_set(&dev->offload_usage, 0);
+#endif
+
 	INIT_LIST_HEAD(&dev->ep0.urb_list);
 	dev->ep0.desc.bLength = USB_DT_ENDPOINT_SIZE;
 	dev->ep0.desc.bDescriptorType = USB_DT_ENDPOINT;
diff --git a/include/linux/usb.h b/include/linux/usb.h
index cfa8005e24f9..9b3f630e763e 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -645,6 +645,7 @@ struct usb3_lpm_parameters {
  *	parent->hub_delay + wHubDelay + tTPTransmissionDelay (40ns)
  *	Will be used as wValue for SetIsochDelay requests.
  * @use_generic_driver: ask driver core to reprobe using the generic driver.
+ * @offload_usage: number of offload activities happening on this usb device.
  *
  * Notes:
  * Usbcore drivers should not set usbdev->state directly.  Instead use
@@ -731,6 +732,10 @@ struct usb_device {
 
 	u16 hub_delay;
 	unsigned use_generic_driver:1;
+
+#ifdef CONFIG_USB_XHCI_SIDEBAND
+	refcount_t offload_usage;
+#endif
 };
 
 #define to_usb_device(__dev)	container_of_const(__dev, struct usb_device, dev)
@@ -837,6 +842,20 @@ static inline void usb_mark_last_busy(struct usb_device *udev)
 { }
 #endif
 
+#ifdef CONFIG_USB_XHCI_SIDEBAND
+extern int usb_offload_get(struct usb_device *udev);
+extern int usb_offload_put(struct usb_device *udev);
+extern 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. */
-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v7 4/5] xhci: sideband: add api to trace sideband usage

[Guan-Yu Lin]

The existing sideband driver only registers sidebands without tracking
their active usage. To address this, new apis are introduced to:
- mark sideband usage: record the sideband usage information in the USB
  device driver.
- query sideband status: provide a means for other drivers to fetch
  sideband activity information on a USB host controller.

Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
---
 drivers/usb/host/xhci-sideband.c  | 82 +++++++++++++++++++++++++++++++
 include/linux/usb/xhci-sideband.h |  6 +++
 2 files changed, 88 insertions(+)

diff --git a/drivers/usb/host/xhci-sideband.c b/drivers/usb/host/xhci-sideband.c
index ffa6f1b825ff..d4931315dcf4 100644
--- a/drivers/usb/host/xhci-sideband.c
+++ b/drivers/usb/host/xhci-sideband.c
@@ -358,6 +358,88 @@ xhci_sideband_interrupter_id(struct xhci_sideband *sb)
 }
 EXPORT_SYMBOL_GPL(xhci_sideband_interrupter_id);
 
+/**
+ * xhci_sideband_get - record a new active sideband instance
+ * @sb: sideband instance for this usb device
+ *
+ * An active sideband indicates that another entity is currently using the host
+ * controller. Inform the usb_device associated with this sideband instance via
+ * usb_offload_get(). This allows the corresponding drivers to dynamically
+ * adjust power management actions based on current sideband activities.
+ *
+ * Returns 0 on success, negative error otherwise.
+ */
+int xhci_sideband_get(struct xhci_sideband *sb)
+{
+	struct usb_device *udev;
+	struct usb_hcd *hcd;
+	int ret = 0;
+
+	if (!sb || !sb->xhci)
+		return -ENODEV;
+
+	hcd = xhci_to_hcd(sb->xhci);
+	udev = sb->vdev->udev;
+	device_lock(&udev->dev);
+	ret = usb_offload_get(udev);
+	device_unlock(&udev->dev);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(xhci_sideband_get);
+
+/**
+ * xhci_sideband_put - record a deactivated sideband instance
+ * @sb: sideband instance for this usb device
+ *
+ * The inverse operation of xhci_sideband_get, which informs the associated
+ * usb_device via usb_offload_put(). This allows the corresponding drivers to
+ * dynamically adjust power management actions based on sideband activities.
+ *
+ * Returns 0 on success, negative error otherwise.
+ */
+int xhci_sideband_put(struct xhci_sideband *sb)
+{
+	struct usb_device *udev;
+	struct usb_hcd *hcd;
+	int ret = 0;
+
+	if (!sb || !sb->xhci)
+		return -ENODEV;
+
+	hcd = xhci_to_hcd(sb->xhci);
+	udev = sb->vdev->udev;
+	device_lock(&udev->dev);
+	ret = usb_offload_put(udev);
+	device_unlock(&udev->dev);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(xhci_sideband_put);
+
+/**
+ * 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.
+ *
+ * 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;
+
+	device_lock(&udev->dev);
+	active = usb_offload_check(udev);
+	device_unlock(&udev->dev);
+
+	return active;
+}
+EXPORT_SYMBOL_GPL(xhci_sideband_check);
+
 /**
  * xhci_sideband_register - register a sideband for a usb device
  * @intf: usb interface associated with the sideband device
diff --git a/include/linux/usb/xhci-sideband.h b/include/linux/usb/xhci-sideband.h
index 72aa17eb068d..6de1d9c161a1 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 */
 
@@ -82,6 +83,11 @@ 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);
+
+int xhci_sideband_get(struct xhci_sideband *sb);
+int xhci_sideband_put(struct xhci_sideband *sb);
+bool xhci_sideband_check(struct usb_hcd *hcd);
+
 int
 xhci_sideband_create_interrupter(struct xhci_sideband *sb, int num_seg,
 				 bool ip_autoclear, u32 imod_interval, int intr_num);
-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v7 5/5] usb: host: enable USB offload during system sleep

[Guan-Yu Lin]

Sharing a USB controller with another entity via xhci-sideband driver
creates power management complexities. To prevent the USB controller
from being inadvertently deactivated while in use by the other entity, a
usage-count based mechanism is implemented. This allows the system to
manage power effectively, ensuring the controller remains available
whenever needed.
In order to maintain full functionality of an offloaded USB devices,
several changes are made within the suspend flow of such devices:
- skip usb_suspend_device() so that the port/hub are still active for
  USB transfers via offloaded path.
- not flushing the endpoints which are used by USB interfaces marked
  with needs_remote_wakeup. Namely, skip usb_suspend_interface() and
  usb_hcd_flush_endpoint() on associated USB interfaces. This reserves a
  pending interrupt urb during system suspend for handling the interrupt
  transfer, which is necessary since remote wakeup doesn't apply in the
  offloaded USB devices when controller is still active.

Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
---
 drivers/usb/core/driver.c         | 37 ++++++++++++++++++++++++++-----
 drivers/usb/core/endpoint.c       |  8 -------
 drivers/usb/dwc3/core.c           | 28 +++++++++++++++++++++++
 drivers/usb/dwc3/core.h           |  1 +
 drivers/usb/host/xhci-plat.c      | 14 ++++++++++++
 include/linux/usb.h               |  8 ++++++-
 include/linux/usb/hcd.h           |  7 ++++++
 sound/usb/qcom/qc_audio_offload.c |  3 +++
 8 files changed, 91 insertions(+), 15 deletions(-)

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 01f6287cf73f..06f9809e2d92 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -1413,19 +1413,32 @@ static int usb_resume_interface(struct usb_device *udev,
  */
 static int usb_suspend_both(struct usb_device *udev, pm_message_t msg)
 {
-	int			status = 0;
-	int			i = 0, n = 0;
-	struct usb_interface	*intf;
+	int			 status = 0;
+	int			 i = 0, n = 0;
+	bool			 offload = false;
+	struct usb_interface	 *intf;
+	struct usb_host_endpoint *ep;
 
 	if (udev->state == USB_STATE_NOTATTACHED ||
 			udev->state == USB_STATE_SUSPENDED)
 		goto done;
 
+#ifdef CONFIG_USB_XHCI_SIDEBAND
+	if (msg.event == PM_EVENT_SUSPEND && usb_offload_check(udev)) {
+		dev_dbg(&udev->dev, "device offload active.\n");
+		offload = true;
+	}
+#endif
+
 	/* 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];
+			if (offload && intf->needs_remote_wakeup) {
+				dev_dbg(&intf->dev, "interface stays active on an offloaded device\n");
+				continue;
+			}
 			status = usb_suspend_interface(udev, intf, msg);
 
 			/* Ignore errors during system sleep transitions */
@@ -1436,7 +1449,8 @@ static int usb_suspend_both(struct usb_device *udev, pm_message_t msg)
 		}
 	}
 	if (status == 0) {
-		status = usb_suspend_device(udev, msg);
+		if (!offload)
+			status = usb_suspend_device(udev, msg);
 
 		/*
 		 * Ignore errors from non-root-hub devices during
@@ -1482,8 +1496,19 @@ 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->ep_out[i]) {
+				ep = udev->ep_out[i];
+				intf = to_usb_interface(ep->ep_dev->dev.parent);
+				if (!(offload && intf->needs_remote_wakeup))
+					usb_hcd_flush_endpoint(udev, ep);
+			}
+
+			if (udev->ep_in[i]) {
+				ep = udev->ep_in[i];
+				intf = to_usb_interface(ep->ep_dev->dev.parent);
+				if (!(offload && intf->needs_remote_wakeup))
+					usb_hcd_flush_endpoint(udev, ep);
+			}
 		}
 	}
 
diff --git a/drivers/usb/core/endpoint.c b/drivers/usb/core/endpoint.c
index e48399401608..658ef39ebcd1 100644
--- a/drivers/usb/core/endpoint.c
+++ b/drivers/usb/core/endpoint.c
@@ -18,14 +18,6 @@
 #include <linux/usb.h>
 #include "usb.h"
 
-struct ep_device {
-	struct usb_endpoint_descriptor *desc;
-	struct usb_device *udev;
-	struct device dev;
-};
-#define to_ep_device(_dev) \
-	container_of(_dev, struct ep_device, dev)
-
 struct ep_attribute {
 	struct attribute attr;
 	ssize_t (*show)(struct usb_device *,
diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 0735881d4650..793fbc030fc4 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -2602,8 +2602,22 @@ static int dwc3_runtime_idle(struct device *dev)
 static int dwc3_suspend(struct device *dev)
 {
 	struct dwc3	*dwc = dev_get_drvdata(dev);
+#ifdef CONFIG_USB_XHCI_SIDEBAND
+	struct platform_device *xhci = dwc->xhci;
+	struct usb_hcd  *hcd;
+#endif
 	int		ret;
 
+#ifdef CONFIG_USB_XHCI_SIDEBAND
+	if (xhci) {
+		hcd = dev_get_drvdata(&xhci->dev);
+		if (xhci_sideband_check(hcd)) {
+			dev_dbg(dev, "sideband instance active.\n");
+			return 0;
+		}
+	}
+#endif
+
 	ret = dwc3_suspend_common(dwc, PMSG_SUSPEND);
 	if (ret)
 		return ret;
@@ -2616,8 +2630,22 @@ static int dwc3_suspend(struct device *dev)
 static int dwc3_resume(struct device *dev)
 {
 	struct dwc3	*dwc = dev_get_drvdata(dev);
+#ifdef CONFIG_USB_XHCI_SIDEBAND
+	struct platform_device *xhci = dwc->xhci;
+	struct usb_hcd  *hcd;
+#endif
 	int		ret = 0;
 
+#ifdef CONFIG_USB_XHCI_SIDEBAND
+	if (xhci) {
+		hcd = dev_get_drvdata(&xhci->dev);
+		if (xhci_sideband_check(hcd)) {
+			dev_dbg(dev, "sideband instance active.\n");
+			return 0;
+		}
+	}
+#endif
+
 	pinctrl_pm_select_default_state(dev);
 
 	pm_runtime_disable(dev);
diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
index 0b6a07202609..57c3e768cdac 100644
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -26,6 +26,7 @@
 #include <linux/usb/ch9.h>
 #include <linux/usb/gadget.h>
 #include <linux/usb/otg.h>
+#include <linux/usb/hcd.h>
 #include <linux/usb/role.h>
 #include <linux/ulpi/interface.h>
 
diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
index b676d4dbcec1..9e01450328d7 100644
--- a/drivers/usb/host/xhci-plat.c
+++ b/drivers/usb/host/xhci-plat.c
@@ -456,6 +456,13 @@ static int xhci_plat_suspend_common(struct device *dev, struct pm_message pmsg)
 	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
 	int ret;
 
+#ifdef CONFIG_USB_XHCI_SIDEBAND
+	if (pmsg.event == PM_EVENT_SUSPEND && xhci_sideband_check(hcd)) {
+		dev_dbg(dev, "sideband instance active.\n");
+		return 0;
+	}
+#endif
+
 	if (pm_runtime_suspended(dev))
 		pm_runtime_resume(dev);
 
@@ -499,6 +506,13 @@ static int xhci_plat_resume_common(struct device *dev, struct pm_message pmsg)
 	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
 	int ret;
 
+#ifdef CONFIG_USB_XHCI_SIDEBAND
+	if (pmsg.event == PM_EVENT_RESUME && xhci_sideband_check(hcd)) {
+		dev_dbg(dev, "sideband instance active.\n");
+		return 0;
+	}
+#endif
+
 	if (!device_may_wakeup(dev) && (xhci->quirks & XHCI_SUSPEND_RESUME_CLKS)) {
 		ret = clk_prepare_enable(xhci->clk);
 		if (ret)
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 9b3f630e763e..c4ff11ad14d5 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -44,7 +44,13 @@ struct usb_driver;
  * Devices may also have class-specific or vendor-specific descriptors.
  */
 
-struct ep_device;
+struct ep_device {
+	struct usb_endpoint_descriptor *desc;
+	struct usb_device *udev;
+	struct device dev;
+};
+#define to_ep_device(_dev) \
+	container_of(_dev, struct ep_device, dev)
 
 /**
  * struct usb_host_endpoint - host-side endpoint descriptor and queue
diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h
index ac95e7c89df5..a9577da6ecff 100644
--- a/include/linux/usb/hcd.h
+++ b/include/linux/usb/hcd.h
@@ -766,6 +766,13 @@ extern struct rw_semaphore ehci_cf_port_reset_rwsem;
 #define USB_EHCI_LOADED		2
 extern unsigned long usb_hcds_loaded;
 
+#if IS_ENABLED(CONFIG_USB_XHCI_SIDEBAND)
+extern bool xhci_sideband_check(struct usb_hcd *hcd);
+#else
+static inline bool xhci_sideband_check(struct usb_hcd *hcd)
+{ return false; }
+#endif
+
 #endif /* __KERNEL__ */
 
 #endif /* __USB_CORE_HCD_H */
diff --git a/sound/usb/qcom/qc_audio_offload.c b/sound/usb/qcom/qc_audio_offload.c
index 7dd7e51109df..7928df8df075 100644
--- a/sound/usb/qcom/qc_audio_offload.c
+++ b/sound/usb/qcom/qc_audio_offload.c
@@ -1619,8 +1619,11 @@ static void handle_uaudio_stream_req(struct qmi_handle *handle,
 			mutex_lock(&chip->mutex);
 			subs->opened = 0;
 			mutex_unlock(&chip->mutex);
+		} else {
+			xhci_sideband_get(uadev[pcm_card_num].si);
 		}
 	} else {
+		xhci_sideband_put(uadev[pcm_card_num].si);
 		info = &uadev[pcm_card_num].info[info_idx];
 		if (info->data_ep_pipe) {
 			ep = usb_pipe_endpoint(uadev[pcm_card_num].udev,
-- 
2.47.1.613.gc27f4b7a9f-goog

Re: [PATCH v7 3/5] usb: add apis for offload usage tracking

[Alan Stern]

On Thu, Jan 09, 2025 at 03:55:07AM +0000, Guan-Yu Lin wrote:
> 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 | 108 ++++++++++++++++++++++++++++++++++++++
>  drivers/usb/core/usb.c    |   4 ++
>  include/linux/usb.h       |  19 +++++++
>  3 files changed, 131 insertions(+)
> 
> diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> index f203fdbfb6f6..01f6287cf73f 100644
> --- a/drivers/usb/core/driver.c
> +++ b/drivers/usb/core/driver.c
> @@ -2037,6 +2037,114 @@ int usb_disable_usb2_hardware_lpm(struct usb_device *udev)
>  
>  #endif /* CONFIG_PM */
>  
> +#ifdef CONFIG_USB_XHCI_SIDEBAND
> +
> +/**
> + * 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.
> + *
> + * The caller must hold @udev's device lock.
> + *
> + * Return: 0 on success. A negative error code otherwise.
> + */
> +int usb_offload_get(struct usb_device *udev)
> +{
> +	int ret;
> +
> +	if (udev->state == USB_STATE_NOTATTACHED ||
> +			udev->state == USB_STATE_SUSPENDED)
> +		return -EAGAIN;
> +
> +	/*
> +	 * offload_usage could only be modified when the device is active, since
> +	 * it will alter the suspend flow of the device.
> +	 */
> +	ret = pm_runtime_get_sync(&udev->dev);

Note that this function will increment the runtime PM reference count 
even if it returns an error.  You probably want to call 
pm_runtime_resume_and_get() instead.  Likewise in usb_offload_put().

> +
> +	if (ret < 0)
> +		return ret;
> +
> +	refcount_inc(&udev->offload_usage);
> +	pm_runtime_put_sync(&udev->dev);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(usb_offload_get);

Alan Stern

Re: [PATCH v7 5/5] usb: host: enable USB offload during system sleep

[Alan Stern]

On Thu, Jan 09, 2025 at 03:55:09AM +0000, Guan-Yu Lin wrote:
> Sharing a USB controller with another entity via xhci-sideband driver
> creates power management complexities. To prevent the USB controller
> from being inadvertently deactivated while in use by the other entity, a
> usage-count based mechanism is implemented. This allows the system to
> manage power effectively, ensuring the controller remains available
> whenever needed.
> In order to maintain full functionality of an offloaded USB devices,
> several changes are made within the suspend flow of such devices:
> - skip usb_suspend_device() so that the port/hub are still active for
>   USB transfers via offloaded path.
> - not flushing the endpoints which are used by USB interfaces marked
>   with needs_remote_wakeup. Namely, skip usb_suspend_interface() and
>   usb_hcd_flush_endpoint() on associated USB interfaces. This reserves a
>   pending interrupt urb during system suspend for handling the interrupt
>   transfer, which is necessary since remote wakeup doesn't apply in the
>   offloaded USB devices when controller is still active.

Does this reasoning apply to interrupt-OUT as well as interrupt-IN?

Or looking at it another way: Since the device's endpoints are being 
used by the coprocessor, should the system flush any of them at all?

Alan Stern

Re: [PATCH v7 3/5] usb: add apis for offload usage tracking

[Guan-Yu Lin]

On Thu, Jan 9, 2025 at 11:04 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Thu, Jan 09, 2025 at 03:55:07AM +0000, Guan-Yu Lin wrote:
> > +     /*
> > +      * offload_usage could only be modified when the device is active, since
> > +      * it will alter the suspend flow of the device.
> > +      */
> > +     ret = pm_runtime_get_sync(&udev->dev);
>
> Note that this function will increment the runtime PM reference count
> even if it returns an error.  You probably want to call
> pm_runtime_resume_and_get() instead.  Likewise in usb_offload_put().
>

Thanks for the heads up! Let me address this in the next patch.

Regards,
Guan-Yu

Re: [PATCH v7 5/5] usb: host: enable USB offload during system sleep

[Guan-Yu Lin]

On Thu, Jan 9, 2025 at 11:08 PM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Thu, Jan 09, 2025 at 03:55:09AM +0000, Guan-Yu Lin wrote:
> > Sharing a USB controller with another entity via xhci-sideband driver
> > creates power management complexities. To prevent the USB controller
> > from being inadvertently deactivated while in use by the other entity, a
> > usage-count based mechanism is implemented. This allows the system to
> > manage power effectively, ensuring the controller remains available
> > whenever needed.
> > In order to maintain full functionality of an offloaded USB devices,
> > several changes are made within the suspend flow of such devices:
> > - skip usb_suspend_device() so that the port/hub are still active for
> >   USB transfers via offloaded path.
> > - not flushing the endpoints which are used by USB interfaces marked
> >   with needs_remote_wakeup. Namely, skip usb_suspend_interface() and
> >   usb_hcd_flush_endpoint() on associated USB interfaces. This reserves a
> >   pending interrupt urb during system suspend for handling the interrupt
> >   transfer, which is necessary since remote wakeup doesn't apply in the
> >   offloaded USB devices when controller is still active.
>
> Does this reasoning apply to interrupt-OUT as well as interrupt-IN?
>

Interrupt-OUT endpoints seem unnecessary in our current use cases. Our
primary concern lies with interrupt-IN endpoints, specifically those
associated with the remote wakeup feature.
Remote wakeup presents a unique challenge within our audio offloading
model during system suspend. Functions typically reliant on remote
wakeup, such as key-events, bypass remote wakeup because the
controller remains active during system suspend. Consequently, these
functions are handled as if the system were active, with events
received by a pending URB. Flushing the endpoint would remove this
pending URB, leaving no mechanism to handle these interrupt events.
Therefore, we should avoid flushing endpoints associated with remote
wakeup to ensure continued functionality for audio offloading during
system suspend.

>
> Or looking at it another way: Since the device's endpoints are being
> used by the coprocessor, should the system flush any of them at all?
>
Our local experiments reveal issues when we flush interrupt endpoints.
For other endpoints, we didn't see any problem. However, since
usb_hcd_flush_endpoint() still modifies the endpoints, it'll be better
to avoid flushing the endpoints associated with the offloaded USB
devices. This could mitigate potential conflicts in the future.

Regards,
Guan-Yu