usb: assign default peer ports for root hubs

Assume that the peer of a superspeed port is the port with the same id
on the shared_hcd root hub.  This identification scheme is required of
external hubs by the USB3 spec [1].  However, for root hubs, tier mismatch
may be in effect [2].  Tier mismatch can only be enumerated via platform
firmware.  For now, simply perform the nominal association.

A new lock 'usb_port_peer_mutex' is introduced to synchronize port
device add/remove with peer lookups.  It protects peering against
changes to hcd->shared_hcd, hcd->self.root_hub, hdev->maxchild, and
port_dev->child pointers.

[1]: usb 3.1 section 10.3.3
[2]: xhci 1.1 appendix D

Cc: Alan Stern <stern@rowland.harvard.edu>
[alan: usb_port_peer_mutex locking scheme]
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/usb/core/hub.h b/drivers/usb/core/hub.h
index 4bd72dd303d5..fcad5f9d12f0 100644
--- a/drivers/usb/core/hub.h
+++ b/drivers/usb/core/hub.h
@@ -82,6 +82,7 @@ struct usb_hub {
  * @child: usb device attached to the port
  * @dev: generic device interface
  * @port_owner: port's owner
+ * @peer: related usb2 and usb3 ports (share the same connector)
  * @connect_type: port's connect type
  * @portnum: port index num based one
  * @power_is_on: port's power state
@@ -91,6 +92,7 @@ struct usb_port {
 	struct usb_device *child;
 	struct device dev;
 	struct usb_dev_state *port_owner;
+	struct usb_port *peer;
 	enum usb_port_connect_type connect_type;
 	u8 portnum;
 	unsigned power_is_on:1;