usb: block suspension of superspeed port while hispeed peer is active

ClearPortFeature(PORT_POWER) on a usb3 port places the port in either a
DSPORT.Powered-off-detect / DSPORT.Powered-off-reset loop, or the
DSPORT.Powered-off state.  There is no way to ensure that RX
terminations will persist in this state, so it is possible a device will
degrade to its usb2 connection.  Prevent this by blocking power-off of a
usb3 port while its usb2 peer is active, and powering on a usb3 port
before its usb2 peer.

By default the latency between peer power-on events is 0.  In order for
the device to not see usb2 active while usb3 is still powering up inject
the hub recommended power_on_good delay.  In support of satisfying the
power_on_good delay outside of hub_power_on() refactor the places where
the delay is consumed to call a new hub_power_on_good_delay() helper.

Finally, because this introduces several new checks for whether a port
is_superspeed, cache that disctinction at port creation so that we don't
need to keep looking up the parent hub device.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
[alan]: add a 'superspeed' flag to the port
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/hub.c

@@ -36,11 +36,6 @@
 #define USB_VENDOR_GENESYS_LOGIC		0x05e3
 #define HUB_QUIRK_CHECK_PORT_AUTOSUSPEND	0x01
 
-static inline int hub_is_superspeed(struct usb_device *hdev)
-{
-	return (hdev->descriptor.bDeviceProtocol == USB_HUB_PR_SS);
-}
-
 /* Protect struct usb_device->state and ->children members
  * Note: Both are also protected by ->dev.sem, except that ->state can
  * change to USB_STATE_NOTATTACHED even when the semaphore isn't held. */
@@ -822,14 +817,9 @@ int usb_hub_clear_tt_buffer(struct urb *urb)
 }
 EXPORT_SYMBOL_GPL(usb_hub_clear_tt_buffer);
 
-/* If do_delay is false, return the number of milliseconds the caller
- * needs to delay.
- */
-static unsigned hub_power_on(struct usb_hub *hub, bool do_delay)
+static void hub_power_on(struct usb_hub *hub, bool do_delay)
 {
 	int port1;
-	unsigned pgood_delay = hub->descriptor->bPwrOn2PwrGood * 2;
-	unsigned delay;
 
 	/* Enable power on each port.  Some hubs have reserved values
 	 * of LPSM (> 2) in their descriptors, even though they are
@@ -848,12 +838,8 @@ static unsigned hub_power_on(struct usb_hub *hub, bool do_delay)
 		else
 			usb_clear_port_feature(hub->hdev, port1,
 						USB_PORT_FEAT_POWER);
-
-	/* Wait at least 100 msec for power to become stable */
-	delay = max(pgood_delay, (unsigned) 100);
 	if (do_delay)
-		msleep(delay);
-	return delay;
+		msleep(hub_power_on_good_delay(hub));
 }
 
 static int hub_hub_status(struct usb_hub *hub,
@@ -1057,7 +1043,9 @@ static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
 		 * for HUB_POST_RESET, but it's easier not to.
 		 */
 		if (type == HUB_INIT) {
-			delay = hub_power_on(hub, false);
+			unsigned delay = hub_power_on_good_delay(hub);
+
+			hub_power_on(hub, false);
 			INIT_DELAYED_WORK(&hub->init_work, hub_init_func2);
 			queue_delayed_work(system_power_efficient_wq,
 					&hub->init_work,

drivers/usb/core/hub.h

@@ -89,6 +89,7 @@ struct usb_hub {
  * @connect_type: port's connect type
  * @location: opaque representation of platform connector location
  * @portnum: port index num based one
+ * @is_superspeed cache super-speed status
  */
 struct usb_port {
 	struct usb_device *child;
@@ -98,6 +99,7 @@ struct usb_port {
 	enum usb_port_connect_type connect_type;
 	usb_port_location_t location;
 	u8 portnum;
+	unsigned int is_superspeed:1;
 };
 
 #define to_usb_port(_dev) \
@@ -125,6 +127,19 @@ static inline bool hub_is_port_power_switchable(struct usb_hub *hub)
 	return (le16_to_cpu(hcs) & HUB_CHAR_LPSM) < HUB_CHAR_NO_LPSM;
 }
 
+static inline int hub_is_superspeed(struct usb_device *hdev)
+{
+	return hdev->descriptor.bDeviceProtocol == USB_HUB_PR_SS;
+}
+
+static inline unsigned hub_power_on_good_delay(struct usb_hub *hub)
+{
+	unsigned delay = hub->descriptor->bPwrOn2PwrGood * 2;
+
+	/* Wait at least 100 msec for power to become stable */
+	return max(delay, 100U);
+}
+
 static inline int hub_port_debounce_be_connected(struct usb_hub *hub,
 		int port1)
 {

drivers/usb/core/port.c

@@ -76,6 +76,7 @@ static int usb_port_runtime_resume(struct device *dev)
 	struct usb_device *hdev = to_usb_device(dev->parent->parent);
 	struct usb_interface *intf = to_usb_interface(dev->parent);
 	struct usb_hub *hub = usb_hub_to_struct_hub(hdev);
+	struct usb_port *peer = port_dev->peer;
 	int port1 = port_dev->portnum;
 	int retval;
 
@@ -86,10 +87,18 @@ static int usb_port_runtime_resume(struct device *dev)
 		return 0;
 	}
 
+	/*
+	 * Power on our usb3 peer before this usb2 port to prevent a usb3
+	 * device from degrading to its usb2 connection
+	 */
+	if (!port_dev->is_superspeed && peer)
+		pm_runtime_get_sync(&peer->dev);
+
 	usb_autopm_get_interface(intf);
 	set_bit(port1, hub->busy_bits);
 
 	retval = usb_hub_set_port_power(hdev, hub, port1, true);
+	msleep(hub_power_on_good_delay(hub));
 	if (port_dev->child && !retval) {
 		/*
 		 * Attempt to wait for usb hub port to be reconnected in order
@@ -107,6 +116,7 @@ static int usb_port_runtime_resume(struct device *dev)
 
 	clear_bit(port1, hub->busy_bits);
 	usb_autopm_put_interface(intf);
+
 	return retval;
 }
 
@@ -116,6 +126,7 @@ static int usb_port_runtime_suspend(struct device *dev)
 	struct usb_device *hdev = to_usb_device(dev->parent->parent);
 	struct usb_interface *intf = to_usb_interface(dev->parent);
 	struct usb_hub *hub = usb_hub_to_struct_hub(hdev);
+	struct usb_port *peer = port_dev->peer;
 	int port1 = port_dev->portnum;
 	int retval;
 
@@ -135,6 +146,15 @@ static int usb_port_runtime_suspend(struct device *dev)
 	usb_clear_port_feature(hdev, port1,	USB_PORT_FEAT_C_ENABLE);
 	clear_bit(port1, hub->busy_bits);
 	usb_autopm_put_interface(intf);
+
+	/*
+	 * Our peer usb3 port may now be able to suspend, so
+	 * asynchronously queue a suspend request to observe that this
+	 * usb2 port is now off.
+	 */
+	if (!port_dev->is_superspeed && peer)
+		pm_runtime_put(&peer->dev);
+
 	return retval;
 }
 #endif
@@ -159,6 +179,7 @@ static struct device_driver usb_port_driver = {
 
 static int link_peers(struct usb_port *left, struct usb_port *right)
 {
+	struct usb_port *ss_port, *hs_port;
 	int rc;
 
 	if (left->peer == right && right->peer == left)
@@ -184,9 +205,36 @@ static int link_peers(struct usb_port *left, struct usb_port *right)
 		return rc;
 	}
 
+	/*
+	 * We need to wake the HiSpeed port to make sure we don't race
+	 * setting ->peer with usb_port_runtime_suspend().  Otherwise we
+	 * may miss a suspend event for the SuperSpeed port.
+	 */
+	if (left->is_superspeed) {
+		ss_port = left;
+		WARN_ON(right->is_superspeed);
+		hs_port = right;
+	} else {
+		ss_port = right;
+		WARN_ON(!right->is_superspeed);
+		hs_port = left;
+	}
+	pm_runtime_get_sync(&hs_port->dev);
+
 	left->peer = right;
 	right->peer = left;
 
+	/*
+	 * The SuperSpeed reference is dropped when the HiSpeed port in
+	 * this relationship suspends, i.e. when it is safe to allow a
+	 * SuperSpeed connection to drop since there is no risk of a
+	 * device degrading to its powered-off HiSpeed connection.
+	 *
+	 * Also, drop the HiSpeed ref taken above.
+	 */
+	pm_runtime_get_sync(&ss_port->dev);
+	pm_runtime_put(&hs_port->dev);
+
 	return 0;
 }
 
@@ -206,14 +254,37 @@ static void link_peers_report(struct usb_port *left, struct usb_port *right)
 
 static void unlink_peers(struct usb_port *left, struct usb_port *right)
 {
+	struct usb_port *ss_port, *hs_port;
+
 	WARN(right->peer != left || left->peer != right,
 			"%s and %s are not peers?\n",
 			dev_name(&left->dev), dev_name(&right->dev));
 
+	/*
+	 * We wake the HiSpeed port to make sure we don't race its
+	 * usb_port_runtime_resume() event which takes a SuperSpeed ref
+	 * when ->peer is !NULL.
+	 */
+	if (left->is_superspeed) {
+		ss_port = left;
+		hs_port = right;
+	} else {
+		ss_port = right;
+		hs_port = left;
+	}
+
+	pm_runtime_get_sync(&hs_port->dev);
+
 	sysfs_remove_link(&left->dev.kobj, "peer");
 	right->peer = NULL;
 	sysfs_remove_link(&right->dev.kobj, "peer");
 	left->peer = NULL;
+
+	/* Drop the SuperSpeed ref held on behalf of the active HiSpeed port */
+	pm_runtime_put(&ss_port->dev);
+
+	/* Drop the ref taken above */
+	pm_runtime_put(&hs_port->dev);
 }
 
 /*
@@ -325,6 +396,8 @@ int usb_hub_create_port_device(struct usb_hub *hub, int port1)
 	port_dev->dev.groups = port_dev_group;
 	port_dev->dev.type = &usb_port_device_type;
 	port_dev->dev.driver = &usb_port_driver;
+	if (hub_is_superspeed(hub->hdev))
+		port_dev->is_superspeed = 1;
 	dev_set_name(&port_dev->dev, "%s-port%d", dev_name(&hub->hdev->dev),
 			port1);
 	retval = device_register(&port_dev->dev);