[PATCH v2 1/3] usb: notify hcd when USB device suspend or resume

[Lu Baolu]

This patch adds two new entries in hc_driver. With these new entries,
USB core can notify host driver when a USB device is about to suspend
or just resumed.

The xHCI spec is designed to allow an xHC implementation to cache the
endpoint state. Caching endpoint state allows an xHC to reduce latency
when handling ERDYs and other USB asynchronous events. However holding
this state in xHC consumes resources and power. The xHCI spec designs
some methods through which host controller driver can hint xHC about
how to optimize its operation, e.g. to determine when it holds state
internally or pushes it out to memory, when to power down logic, etc.

When a USB device is going to suspend, states of all endpoints cached
in the xHC should be pushed out to memory to save power and resources.
Vice versa, when a USB device resumes, those states should be brought
back to the cache. USB core suspends or resumes a USB device by sending
set/clear port feature requests to the parent hub where the USB device
is connected. Unfortunately, these operations are transparent to xHCI
driver unless the USB device is plugged in a root port. This patch
utilizes the callback entries to notify xHCI driver whenever a USB
device suspends or resumes.

It is harmless if a USB devices under USB 3.0 host controller suspends
or resumes without a notification to hcd driver. However there may be
less opportunities for power savings and there may be increased latency
for restarting an endpoint. The precise impact will be different for
each xHC implementation. It all depends on what an implementation does
with the hints.

Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
 drivers/usb/core/hcd.c  | 29 +++++++++++++++++++++++++++++
 drivers/usb/core/hub.c  | 16 ++++++++++++++++
 include/linux/usb/hcd.h | 10 +++++++++-
 3 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 45a915c..a4cfc2d 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -2289,6 +2289,35 @@ void usb_hcd_resume_root_hub (struct usb_hcd *hcd)
 }
 EXPORT_SYMBOL_GPL(usb_hcd_resume_root_hub);
 
+/**
+ * hcd_suspend_notify - notify hcd driver when a device is going to suspend
+ * @udev: USB device to be suspended
+ * @msg: Power Management message describing this state transition
+ *
+ * Call back to hcd driver to notify that a USB device is going to suspend.
+ */
+void hcd_suspend_notify(struct usb_device *udev, pm_message_t msg)
+{
+	struct usb_hcd *hcd = bus_to_hcd(udev->bus);
+
+	if (hcd->driver->device_suspend)
+		hcd->driver->device_suspend(hcd, udev, msg);
+}
+
+/**
+ * hcd_resume_notify - notify hcd driver when a device is just resumed
+ * @udev: USB device just resumed
+ * @msg: Power Management message describing this state transition
+ *
+ * Call back to hcd driver to notify that a USB device is just resumed.
+ */
+void hcd_resume_notify(struct usb_device *udev, pm_message_t msg)
+{
+	struct usb_hcd *hcd = bus_to_hcd(udev->bus);
+
+	if (hcd->driver->device_resume)
+		hcd->driver->device_resume(hcd, udev, msg);
+}
 #endif	/* CONFIG_PM */
 
 /*-------------------------------------------------------------------------*/
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 3b71516..ed22b51 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -3144,6 +3144,14 @@ int usb_port_suspend(struct usb_device *udev, pm_message_t msg)
 			goto err_lpm3;
 	}
 
+	/*
+	 * Call back to hcd if it expects. xHCI compatible host controller
+	 * driver expects to be notified prior to selectively suspending a
+	 * device. xHCI hcd could optimize the endpoint cache for power
+	 * saving purpose. Refer to 4.15.1.1 of xHCI 1.1 for more information.
+	 */
+	hcd_suspend_notify(udev, msg);
+
 	/* see 7.1.7.6 */
 	if (hub_is_superspeed(hub->hdev))
 		status = hub_set_port_link_state(hub, port1, USB_SS_PORT_LS_U3);
@@ -3169,6 +3177,8 @@ int usb_port_suspend(struct usb_device *udev, pm_message_t msg)
 	if (status) {
 		dev_dbg(&port_dev->dev, "can't suspend, status %d\n", status);
 
+		hcd_resume_notify(udev, msg);
+
 		/* Try to enable USB3 LPM and LTM again */
 		usb_unlocked_enable_lpm(udev);
  err_lpm3:
@@ -3422,6 +3432,12 @@ int usb_port_resume(struct usb_device *udev, pm_message_t msg)
 	}
 
  SuspendCleared:
+	/* Call back to hcd if it expects. xHCI compatible host controller
+	 * driver expects to be notified after a device is resumed. xHCI
+	 * hcd could optimize the endpoint cache for latency reducing
+	 * purpose. Refer to 4.15.1.1 of xHCI 1.1 for more information.
+	 */
+	hcd_resume_notify(udev, msg);
 	if (status == 0) {
 		udev->port_is_suspended = 0;
 		if (hub_is_superspeed(hub->hdev)) {
diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h
index 68b1e83..621d9b7 100644
--- a/include/linux/usb/hcd.h
+++ b/include/linux/usb/hcd.h
@@ -383,7 +383,13 @@ struct hc_driver {
 	int	(*find_raw_port_number)(struct usb_hcd *, int);
 	/* Call for power on/off the port if necessary */
 	int	(*port_power)(struct usb_hcd *hcd, int portnum, bool enable);
-
+	/* Call back to hcd when a USB device is going to suspend or just
+	 * resumed.
+	 */
+	void	(*device_suspend)(struct usb_hcd *, struct usb_device *udev,
+			pm_message_t msg);
+	void	(*device_resume)(struct usb_hcd *, struct usb_device *udev,
+			pm_message_t msg);
 };
 
 static inline int hcd_giveback_urb_in_bh(struct usb_hcd *hcd)
@@ -632,6 +638,8 @@ extern void usb_root_hub_lost_power(struct usb_device *rhdev);
 extern int hcd_bus_suspend(struct usb_device *rhdev, pm_message_t msg);
 extern int hcd_bus_resume(struct usb_device *rhdev, pm_message_t msg);
 extern void usb_hcd_resume_root_hub(struct usb_hcd *hcd);
+extern void hcd_suspend_notify(struct usb_device *udev, pm_message_t msg);
+extern void hcd_resume_notify(struct usb_device *udev, pm_message_t msg);
 #else
 static inline void usb_hcd_resume_root_hub(struct usb_hcd *hcd)
 {
-- 
2.1.0

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