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
  host controller driver and 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  | 74 +++++++++++++++++++++++++++++++
 include/linux/usb/hcd.h           |  4 ++
 include/linux/usb/xhci-sideband.h |  5 +++
 3 files changed, 83 insertions(+)

diff --git a/drivers/usb/host/xhci-sideband.c b/drivers/usb/host/xhci-sideband.c
index d04cf0af57ae..29501e5d020f 100644
--- a/drivers/usb/host/xhci-sideband.c
+++ b/drivers/usb/host/xhci-sideband.c
@@ -334,6 +334,80 @@ xhci_sideband_interrupter_id(struct xhci_sideband *sb)
 }
 EXPORT_SYMBOL_GPL(xhci_sideband_interrupter_id);
 
+/**
+ * xhci_sideband_get - notify related drivers there's a new active sideband
+ * @sb: sideband instance for this usb device
+ *
+ * An active sideband indicates that another entity is currently using the host
+ * controller. Notify the host controller and related usb devices by increasing
+ * their sb_usage_count. This allows the corresponding drivers to dynamically
+ * adjust power management actions based on current sideband activity.
+ *
+ * Returns 0 on success, negative error otherwise
+ */
+int xhci_sideband_get(struct xhci_sideband *sb)
+{
+	struct usb_hcd *hcd;
+	struct usb_device *udev;
+
+	if (!sb || !sb->xhci)
+		return -ENODEV;
+
+	hcd = xhci_to_hcd(sb->xhci);
+	atomic_inc(&hcd->sb_usage_count);
+
+	udev = sb->vdev->udev;
+	usb_sideband_get(udev);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(xhci_sideband_get);
+
+/**
+ * xhci_sideband_put - notify related drivers there's a sideband deactivated
+ * @sb: sideband instance for this usb device
+ *
+ * The inverse operation of xhci_sideband_get, which notifies the host
+ * controller and related usb devices by decreasing their sb_usage_count. This
+ * allows the corresponding drivers to dynamically adjust power management
+ * actions based on current sideband activity.
+ *
+ * Returns 0 on success, negative error otherwise
+ */
+int xhci_sideband_put(struct xhci_sideband *sb)
+{
+	struct usb_hcd *hcd;
+	struct usb_device *udev;
+
+	if (!sb || !sb->xhci)
+		return -ENODEV;
+
+	hcd = xhci_to_hcd(sb->xhci);
+	atomic_dec(&hcd->sb_usage_count);
+
+	udev = sb->vdev->udev;
+	usb_sideband_put(udev);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(xhci_sideband_put);
+
+/**
+ * xhci_sideband_check - check sideband activities on the host controller
+ * @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 right now. This information
+ * could be used for power management or other forms or resource management.
+ *
+ * Returns true on any active sideband existence, false otherwise
+ */
+bool xhci_sideband_check(struct usb_hcd *hcd)
+{
+	return !!atomic_read(&hcd->sb_usage_count);
+}
+EXPORT_SYMBOL_GPL(xhci_sideband_check);
+
 /**
  * xhci_sideband_register - register a sideband for a usb device
  * @udev: usb device to be accessed via sideband
diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h
index ac95e7c89df5..8b8106b9a31e 100644
--- a/include/linux/usb/hcd.h
+++ b/include/linux/usb/hcd.h
@@ -84,6 +84,10 @@ struct usb_hcd {
 	struct urb		*status_urb;	/* the current status urb */
 #ifdef CONFIG_PM
 	struct work_struct	wakeup_work;	/* for remote wakeup */
+#ifdef CONFIG_USB_XHCI_SIDEBAND
+	/* Number of active sideband accessing the host controller. */
+	atomic_t		sb_usage_count;
+#endif
 #endif
 	struct work_struct	died_work;	/* for when the device dies */
 
diff --git a/include/linux/usb/xhci-sideband.h b/include/linux/usb/xhci-sideband.h
index f0223c5535e0..4850fc826e00 100644
--- a/include/linux/usb/xhci-sideband.h
+++ b/include/linux/usb/xhci-sideband.h
@@ -12,6 +12,7 @@
 
 #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 */
 
@@ -57,6 +58,10 @@ xhci_sideband_get_endpoint_buffer(struct xhci_sideband *sb,
 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);
-- 
2.47.0.rc0.187.ge670bccf7e-goog

On Wed, Oct 09, 2024 at 05:42:58AM +0000, Guan-Yu Lin wrote:
> --- a/include/linux/usb/hcd.h
> +++ b/include/linux/usb/hcd.h
> @@ -84,6 +84,10 @@ struct usb_hcd {
>  	struct urb		*status_urb;	/* the current status urb */
>  #ifdef CONFIG_PM
>  	struct work_struct	wakeup_work;	/* for remote wakeup */
> +#ifdef CONFIG_USB_XHCI_SIDEBAND
> +	/* Number of active sideband accessing the host controller. */
> +	atomic_t		sb_usage_count;

It's a reference count, use refcount_t please.

On Wed, Oct 9, 2024 at 8:48 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Wed, Oct 09, 2024 at 05:42:58AM +0000, Guan-Yu Lin wrote:
> > --- a/include/linux/usb/hcd.h
> > +++ b/include/linux/usb/hcd.h
> > @@ -84,6 +84,10 @@ struct usb_hcd {
> >       struct urb              *status_urb;    /* the current status urb */
> >  #ifdef CONFIG_PM
> >       struct work_struct      wakeup_work;    /* for remote wakeup */
> > +#ifdef CONFIG_USB_XHCI_SIDEBAND
> > +     /* Number of active sideband accessing the host controller. */
> > +     atomic_t                sb_usage_count;
>
> It's a reference count, use refcount_t please.

Appreciate the clear instructions, let me fix it in the next version.