linux/net/mac80211/mesh_sync.c
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   1/*
   2 * Copyright 2011-2012, Pavel Zubarev <pavel.zubarev@gmail.com>
   3 * Copyright 2011-2012, Marco Porsch <marco.porsch@s2005.tu-chemnitz.de>
   4 * Copyright 2011-2012, cozybit Inc.
   5 *
   6 * This program is free software; you can redistribute it and/or modify
   7 * it under the terms of the GNU General Public License version 2 as
   8 * published by the Free Software Foundation.
   9 */
  10
  11#include "ieee80211_i.h"
  12#include "mesh.h"
  13#include "driver-ops.h"
  14
  15/* This is not in the standard.  It represents a tolerable tbtt drift below
  16 * which we do no TSF adjustment.
  17 */
  18#define TOFFSET_MINIMUM_ADJUSTMENT 10
  19
  20/* This is not in the standard. It is a margin added to the
  21 * Toffset setpoint to mitigate TSF overcorrection
  22 * introduced by TSF adjustment latency.
  23 */
  24#define TOFFSET_SET_MARGIN 20
  25
  26/* This is not in the standard.  It represents the maximum Toffset jump above
  27 * which we'll invalidate the Toffset setpoint and choose a new setpoint.  This
  28 * could be, for instance, in case a neighbor is restarted and its TSF counter
  29 * reset.
  30 */
  31#define TOFFSET_MAXIMUM_ADJUSTMENT 30000                /* 30 ms */
  32
  33struct sync_method {
  34        u8 method;
  35        struct ieee80211_mesh_sync_ops ops;
  36};
  37
  38/**
  39 * mesh_peer_tbtt_adjusting - check if an mp is currently adjusting its TBTT
  40 *
  41 * @ie: information elements of a management frame from the mesh peer
  42 */
  43static bool mesh_peer_tbtt_adjusting(struct ieee802_11_elems *ie)
  44{
  45        return (ie->mesh_config->meshconf_cap &
  46            MESHCONF_CAPAB_TBTT_ADJUSTING) != 0;
  47}
  48
  49void mesh_sync_adjust_tbtt(struct ieee80211_sub_if_data *sdata)
  50{
  51        struct ieee80211_local *local = sdata->local;
  52        struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
  53        /* sdata->vif.bss_conf.beacon_int in 1024us units, 0.04% */
  54        u64 beacon_int_fraction = sdata->vif.bss_conf.beacon_int * 1024 / 2500;
  55        u64 tsf;
  56        u64 tsfdelta;
  57
  58        spin_lock_bh(&ifmsh->sync_offset_lock);
  59        if (ifmsh->sync_offset_clockdrift_max < beacon_int_fraction) {
  60                msync_dbg(sdata, "TBTT : max clockdrift=%lld; adjusting\n",
  61                          (long long) ifmsh->sync_offset_clockdrift_max);
  62                tsfdelta = -ifmsh->sync_offset_clockdrift_max;
  63                ifmsh->sync_offset_clockdrift_max = 0;
  64        } else {
  65                msync_dbg(sdata, "TBTT : max clockdrift=%lld; adjusting by %llu\n",
  66                          (long long) ifmsh->sync_offset_clockdrift_max,
  67                          (unsigned long long) beacon_int_fraction);
  68                tsfdelta = -beacon_int_fraction;
  69                ifmsh->sync_offset_clockdrift_max -= beacon_int_fraction;
  70        }
  71        spin_unlock_bh(&ifmsh->sync_offset_lock);
  72
  73        tsf = drv_get_tsf(local, sdata);
  74        if (tsf != -1ULL)
  75                drv_set_tsf(local, sdata, tsf + tsfdelta);
  76}
  77
  78static void mesh_sync_offset_rx_bcn_presp(struct ieee80211_sub_if_data *sdata,
  79                                   u16 stype,
  80                                   struct ieee80211_mgmt *mgmt,
  81                                   struct ieee802_11_elems *elems,
  82                                   struct ieee80211_rx_status *rx_status)
  83{
  84        struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
  85        struct ieee80211_local *local = sdata->local;
  86        struct sta_info *sta;
  87        u64 t_t, t_r;
  88
  89        WARN_ON(ifmsh->mesh_sp_id != IEEE80211_SYNC_METHOD_NEIGHBOR_OFFSET);
  90
  91        /* standard mentions only beacons */
  92        if (stype != IEEE80211_STYPE_BEACON)
  93                return;
  94
  95        /* The current tsf is a first approximation for the timestamp
  96         * for the received beacon.  Further down we try to get a
  97         * better value from the rx_status->mactime field if
  98         * available. Also we have to call drv_get_tsf() before
  99         * entering the rcu-read section.*/
 100        t_r = drv_get_tsf(local, sdata);
 101
 102        rcu_read_lock();
 103        sta = sta_info_get(sdata, mgmt->sa);
 104        if (!sta)
 105                goto no_sync;
 106
 107        /* check offset sync conditions (13.13.2.2.1)
 108         *
 109         * TODO also sync to
 110         * dot11MeshNbrOffsetMaxNeighbor non-peer non-MBSS neighbors
 111         */
 112
 113        if (elems->mesh_config && mesh_peer_tbtt_adjusting(elems)) {
 114                clear_sta_flag(sta, WLAN_STA_TOFFSET_KNOWN);
 115                msync_dbg(sdata, "STA %pM : is adjusting TBTT\n", sta->sta.addr);
 116                goto no_sync;
 117        }
 118
 119        if (rx_status->flag & RX_FLAG_MACTIME_MPDU && rx_status->mactime) {
 120                /*
 121                 * The mactime is defined as the time the first data symbol
 122                 * of the frame hits the PHY, and the timestamp of the beacon
 123                 * is defined as "the time that the data symbol containing the
 124                 * first bit of the timestamp is transmitted to the PHY plus
 125                 * the transmitting STA's delays through its local PHY from the
 126                 * MAC-PHY interface to its interface with the WM" (802.11
 127                 * 11.1.2)
 128                 *
 129                 * T_r, in 13.13.2.2.2, is just defined as "the frame reception
 130                 * time" but we unless we interpret that time to be the same
 131                 * time of the beacon timestamp, the offset calculation will be
 132                 * off.  Below we adjust t_r to be "the time at which the first
 133                 * symbol of the timestamp element in the beacon is received".
 134                 * This correction depends on the rate.
 135                 *
 136                 * Based on similar code in ibss.c
 137                 */
 138                int rate;
 139
 140                if (rx_status->flag & RX_FLAG_HT) {
 141                        /* TODO:
 142                         * In principle there could be HT-beacons (Dual Beacon
 143                         * HT Operation options), but for now ignore them and
 144                         * just use the primary (i.e. non-HT) beacons for
 145                         * synchronization.
 146                         * */
 147                        goto no_sync;
 148                } else
 149                        rate = local->hw.wiphy->bands[rx_status->band]->
 150                                bitrates[rx_status->rate_idx].bitrate;
 151
 152                /* 24 bytes of header * 8 bits/byte *
 153                 * 10*(100 Kbps)/Mbps / rate (100 Kbps)*/
 154                t_r = rx_status->mactime + (24 * 8 * 10 / rate);
 155        }
 156
 157        /* Timing offset calculation (see 13.13.2.2.2) */
 158        t_t = le64_to_cpu(mgmt->u.beacon.timestamp);
 159        sta->t_offset = t_t - t_r;
 160
 161        if (test_sta_flag(sta, WLAN_STA_TOFFSET_KNOWN)) {
 162                s64 t_clockdrift = sta->t_offset_setpoint
 163                                   - sta->t_offset;
 164                msync_dbg(sdata,
 165                          "STA %pM : sta->t_offset=%lld, sta->t_offset_setpoint=%lld, t_clockdrift=%lld\n",
 166                          sta->sta.addr,
 167                          (long long) sta->t_offset,
 168                          (long long)
 169                          sta->t_offset_setpoint,
 170                          (long long) t_clockdrift);
 171
 172                if (t_clockdrift > TOFFSET_MAXIMUM_ADJUSTMENT ||
 173                        t_clockdrift < -TOFFSET_MAXIMUM_ADJUSTMENT) {
 174                        msync_dbg(sdata,
 175                                  "STA %pM : t_clockdrift=%lld too large, setpoint reset\n",
 176                                  sta->sta.addr,
 177                                  (long long) t_clockdrift);
 178                        clear_sta_flag(sta, WLAN_STA_TOFFSET_KNOWN);
 179                        goto no_sync;
 180                }
 181
 182                rcu_read_unlock();
 183
 184                spin_lock_bh(&ifmsh->sync_offset_lock);
 185                if (t_clockdrift >
 186                    ifmsh->sync_offset_clockdrift_max)
 187                        ifmsh->sync_offset_clockdrift_max
 188                                = t_clockdrift;
 189                spin_unlock_bh(&ifmsh->sync_offset_lock);
 190
 191        } else {
 192                sta->t_offset_setpoint = sta->t_offset - TOFFSET_SET_MARGIN;
 193                set_sta_flag(sta, WLAN_STA_TOFFSET_KNOWN);
 194                msync_dbg(sdata,
 195                          "STA %pM : offset was invalid, sta->t_offset=%lld\n",
 196                          sta->sta.addr,
 197                          (long long) sta->t_offset);
 198                rcu_read_unlock();
 199        }
 200        return;
 201
 202no_sync:
 203        rcu_read_unlock();
 204}
 205
 206static void mesh_sync_offset_adjust_tbtt(struct ieee80211_sub_if_data *sdata)
 207{
 208        struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
 209
 210        WARN_ON(ifmsh->mesh_sp_id
 211                != IEEE80211_SYNC_METHOD_NEIGHBOR_OFFSET);
 212        BUG_ON(!rcu_read_lock_held());
 213
 214        spin_lock_bh(&ifmsh->sync_offset_lock);
 215
 216        if (ifmsh->sync_offset_clockdrift_max >
 217                TOFFSET_MINIMUM_ADJUSTMENT) {
 218                /* Since ajusting the tsf here would
 219                 * require a possibly blocking call
 220                 * to the driver tsf setter, we punt
 221                 * the tsf adjustment to the mesh tasklet
 222                 */
 223                msync_dbg(sdata,
 224                          "TBTT : kicking off TBTT adjustment with clockdrift_max=%lld\n",
 225                          ifmsh->sync_offset_clockdrift_max);
 226                set_bit(MESH_WORK_DRIFT_ADJUST,
 227                        &ifmsh->wrkq_flags);
 228        } else {
 229                msync_dbg(sdata,
 230                          "TBTT : max clockdrift=%lld; too small to adjust\n",
 231                          (long long)ifmsh->sync_offset_clockdrift_max);
 232                ifmsh->sync_offset_clockdrift_max = 0;
 233        }
 234        spin_unlock_bh(&ifmsh->sync_offset_lock);
 235}
 236
 237static const u8 *mesh_get_vendor_oui(struct ieee80211_sub_if_data *sdata)
 238{
 239        struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
 240        u8 offset;
 241
 242        if (!ifmsh->ie || !ifmsh->ie_len)
 243                return NULL;
 244
 245        offset = ieee80211_ie_split_vendor(ifmsh->ie,
 246                                        ifmsh->ie_len, 0);
 247
 248        if (!offset)
 249                return NULL;
 250
 251        return ifmsh->ie + offset + 2;
 252}
 253
 254static void mesh_sync_vendor_rx_bcn_presp(struct ieee80211_sub_if_data *sdata,
 255                                   u16 stype,
 256                                   struct ieee80211_mgmt *mgmt,
 257                                   struct ieee802_11_elems *elems,
 258                                   struct ieee80211_rx_status *rx_status)
 259{
 260        const u8 *oui;
 261
 262        WARN_ON(sdata->u.mesh.mesh_sp_id != IEEE80211_SYNC_METHOD_VENDOR);
 263        msync_dbg(sdata, "called mesh_sync_vendor_rx_bcn_presp\n");
 264        oui = mesh_get_vendor_oui(sdata);
 265        /*  here you would implement the vendor offset tracking for this oui */
 266}
 267
 268static void mesh_sync_vendor_adjust_tbtt(struct ieee80211_sub_if_data *sdata)
 269{
 270        const u8 *oui;
 271
 272        WARN_ON(sdata->u.mesh.mesh_sp_id != IEEE80211_SYNC_METHOD_VENDOR);
 273        msync_dbg(sdata, "called mesh_sync_vendor_adjust_tbtt\n");
 274        oui = mesh_get_vendor_oui(sdata);
 275        /*  here you would implement the vendor tsf adjustment for this oui */
 276}
 277
 278/* global variable */
 279static struct sync_method sync_methods[] = {
 280        {
 281                .method = IEEE80211_SYNC_METHOD_NEIGHBOR_OFFSET,
 282                .ops = {
 283                        .rx_bcn_presp = &mesh_sync_offset_rx_bcn_presp,
 284                        .adjust_tbtt = &mesh_sync_offset_adjust_tbtt,
 285                }
 286        },
 287        {
 288                .method = IEEE80211_SYNC_METHOD_VENDOR,
 289                .ops = {
 290                        .rx_bcn_presp = &mesh_sync_vendor_rx_bcn_presp,
 291                        .adjust_tbtt = &mesh_sync_vendor_adjust_tbtt,
 292                }
 293        },
 294};
 295
 296struct ieee80211_mesh_sync_ops *ieee80211_mesh_sync_ops_get(u8 method)
 297{
 298        struct ieee80211_mesh_sync_ops *ops = NULL;
 299        u8 i;
 300
 301        for (i = 0 ; i < ARRAY_SIZE(sync_methods); ++i) {
 302                if (sync_methods[i].method == method) {
 303                        ops = &sync_methods[i].ops;
 304                        break;
 305                }
 306        }
 307        return ops;
 308}
 309
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