IB: Add caching of ports' LMC

Add an LMC cache to struct ib_device, and add a function
ib_get_cached_lmc() to query the cache.

Signed-off-by: Jack Morgenstein <jackm@mellanox.co.il>
Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

include/rdma/ib_cache.h

diff --git a/include/rdma/ib_cache.h b/include/rdma/ib_cache.h
index 5bf9834f..f179d23 100644
--- a/include/rdma/ib_cache.h
+++ b/include/rdma/ib_cache.h
@@ -102,4 +102,17 @@
 			u16                  pkey,
 			u16                 *index);
 
+/**
+ * ib_get_cached_lmc - Returns a cached lmc table entry
+ * @device: The device to query.
+ * @port_num: The port number of the device to query.
+ * @lmc: The lmc value for the specified port for that device.
+ *
+ * ib_get_cached_lmc() fetches the specified lmc table entry stored in
+ * the local software cache.
+ */
+int ib_get_cached_lmc(struct ib_device *device,
+		      u8                port_num,
+		      u8                *lmc);
+
 #endif /* _IB_CACHE_H */