[PATCH v4 3/5] usb: add apis for sideband uasge tracking

[Guan-Yu Lin <guanyulin@google.com>]

Introduce sb_usage_count and corresponding apis to track sideband usage
on each usb_device. A sideband refers to the co-processor that accesses
the usb_device via shared control on the same USB host controller. To
optimize power usage, it's essential to monitor whether ther sideband is
actively using the usb_device. 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 | 54 +++++++++++++++++++++++++++++++++++++++
 include/linux/usb.h       | 13 ++++++++++
 2 files changed, 67 insertions(+)

diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index 0c3f12daac79..c1ba5ed15214 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -1673,6 +1673,60 @@ void usb_disable_autosuspend(struct usb_device *udev)
 }
 EXPORT_SYMBOL_GPL(usb_disable_autosuspend);
 
+/**
+ * usb_sideband_get - notify usb driver there's a new active sideband
+ * @udev: the usb_device which has an active sideband
+ *
+ * An active sideband indicates that another entity is currently using the usb
+ * device. Notify the usb device by increasing the sb_usage_count. This allows
+ * usb driver to adjust power management policy based on sideband activities.
+ */
+void usb_sideband_get(struct usb_device *udev)
+{
+	struct usb_device *parent = udev;
+
+	do {
+		atomic_inc(&parent->sb_usage_count);
+		parent = parent->parent;
+	} while (parent);
+}
+EXPORT_SYMBOL_GPL(usb_sideband_get);
+
+/**
+ * usb_sideband_put - notify usb driver there's a sideband deactivated
+ * @udev: the usb_device which has a sideband deactivated
+ *
+ * The inverse operation of usb_sideband_get, which notifies the usb device by
+ * decreasing the sb_usage_count. This allows usb driver to adjust power
+ * management policy based on sideband activities.
+ */
+void usb_sideband_put(struct usb_device *udev)
+{
+	struct usb_device *parent = udev;
+
+	do {
+		atomic_dec(&parent->sb_usage_count);
+		parent = parent->parent;
+	} while (parent);
+}
+EXPORT_SYMBOL_GPL(usb_sideband_put);
+
+/**
+ * usb_sideband_check - check sideband activities on the host controller
+ * @udev: the usb_device which has a sideband deactivated
+ *
+ * Check if there are any sideband activity on the USB device 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 usb_sideband_check(struct usb_device *udev)
+{
+	return !!atomic_read(&udev->sb_usage_count);
+}
+EXPORT_SYMBOL_GPL(usb_sideband_check);
+
 /**
  * usb_autosuspend_device - delayed autosuspend of a USB device and its interfaces
  * @udev: the usb_device to autosuspend
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 672d8fc2abdb..5b9fea378960 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.
+ * @sb_usage_count: number of active sideband accessing this usb device.
  *
  * Notes:
  * Usbcore drivers should not set usbdev->state directly.  Instead use
@@ -731,6 +732,8 @@ struct usb_device {
 
 	u16 hub_delay;
 	unsigned use_generic_driver:1;
+
+	atomic_t sb_usage_count;
 };
 
 #define to_usb_device(__dev)	container_of_const(__dev, struct usb_device, dev)
@@ -798,6 +801,9 @@ static inline int usb_acpi_port_lpm_incapable(struct usb_device *hdev, int index
 #ifdef CONFIG_PM
 extern void usb_enable_autosuspend(struct usb_device *udev);
 extern void usb_disable_autosuspend(struct usb_device *udev);
+extern void usb_sideband_get(struct usb_device *udev);
+extern void usb_sideband_put(struct usb_device *udev);
+extern bool usb_sideband_check(struct usb_device *udev);
 
 extern int usb_autopm_get_interface(struct usb_interface *intf);
 extern void usb_autopm_put_interface(struct usb_interface *intf);
@@ -818,6 +824,13 @@ static inline int usb_enable_autosuspend(struct usb_device *udev)
 static inline int usb_disable_autosuspend(struct usb_device *udev)
 { return 0; }
 
+static inline int usb_sideband_get(struct usb_device *udev)
+{ return 0; }
+static inline int usb_sideband_put(struct usb_device *udev)
+{ return 0; }
+static inline bool usb_sideband_check(struct usb_device *udev)
+{ return false; }
+
 static inline int usb_autopm_get_interface(struct usb_interface *intf)
 { return 0; }
 static inline int usb_autopm_get_interface_async(struct usb_interface *intf)
-- 
2.47.0.rc0.187.ge670bccf7e-goog