xhci: sideband: add api to trace sideband usage

The existing sideband driver only registers sidebands without tracking
their active usage. To address this, sideband will now record its active
usage when it creates/removes interrupters. In addition, a new api is
introduced to provide a means for other dirvers to fetch sideband
activity information on a USB host controller.

Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
Link: https://lore.kernel.org/r/20250911142051.90822-4-guanyulin@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250911142051.90822-4-guanyulin@google.com

2 files changed, 45 insertions, 0 deletions

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/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);