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>

3 files changed, 93 insertions, 17 deletions

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 31a492a4a881..e492bca74425 100644
--- a/drivers/usb/core/hub.c
+++ b/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,
diff --git a/drivers/usb/core/hub.h b/drivers/usb/core/hub.h
index 3ef1c2e435cc..906c355e0631 100644
--- a/drivers/usb/core/hub.h
+++ b/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)
 {
diff --git a/drivers/usb/core/port.c b/drivers/usb/core/port.c
index 795778c71e31..827b0d38f73d 100644
--- a/drivers/usb/core/port.c
+++ b/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);