mac80211: Implement mesh synchronization framework

This patch adds MBSS extensible synchronization framework (Sec.
13.13.2 of IEEE Std. 802.11-2012).

The framework is implemented via an ops table which defines the
following functions:

    rx_bcn_presp() - this is called every time a mesh beacon is
received.
    adjust_tbtt() - this is called immediately before a beacon is about
to be transmitted.

The default neighbor offset synchronization defined in the standard is
implemented.  We also provide template functions for vendor specific
methods.

When neighbor offset synchronization is active (which is the default)
mesh neighbors in the same MBSS will track timing offsets to each other
and compensate clock drift.

In our tests we observed that this mesh synchronization implementation
successfully corrected drifts between stations of ~2PPM while
introducing a jitter of ~20us.

It is also possible to test this framework on mac80211_hwsim simulated
phys to see how it behaves under different topologies, over poor links,
etc.

Signed-off-by: Marco Porsch <marco.porsch@s2005.tu-chemnitz.de>
Signed-off-by: Pavel Zubarev <pavel.zubarev@gmail.com>
Signed-off-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 8e7af7cee013..ea9623cbd969 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -554,6 +554,24 @@ struct ieee80211_if_ibss {
         } state;
 };
 
+/**
+ * struct ieee80211_mesh_sync_ops - Extensible synchronization framework interface
+ *
+ * these declarations define the interface, which enables
+ * vendor-specific mesh synchronization
+ *
+ */
+struct ieee802_11_elems;
+struct ieee80211_mesh_sync_ops {
+        void (*rx_bcn_presp)(struct ieee80211_sub_if_data *sdata,
+                             u16 stype,
+                             struct ieee80211_mgmt *mgmt,
+                             struct ieee802_11_elems *elems,
+                             struct ieee80211_rx_status *rx_status);
+        void (*adjust_tbtt)(struct ieee80211_sub_if_data *sdata);
+        /* add other framework functions here */
+};
+
 struct ieee80211_if_mesh {
         struct timer_list housekeeping_timer;
         struct timer_list mesh_path_timer;
@@ -602,6 +620,11 @@ struct ieee80211_if_mesh {
                 IEEE80211_MESH_SEC_AUTHED = 0x1,
                 IEEE80211_MESH_SEC_SECURED = 0x2,
         } security;
+        /* Extensible Synchronization Framework */
+        struct ieee80211_mesh_sync_ops *sync_ops;
+        s64 sync_offset_clockdrift_max;
+        spinlock_t sync_offset_lock;
+        bool adjusting_tbtt;
 };
 
 #ifdef CONFIG_MAC80211_MESH