mesh_sync.c

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/*
 * Copyright 2011-2012, Pavel Zubarev <[email protected]>
 * Copyright 2011-2012, Marco Porsch <[email protected]>
 * Copyright 2011-2012, cozybit Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include "ieee80211_i.h"
#include "mesh.h"
#include "driver-ops.h"

/* This is not in the standard.  It represents a tolerable tbtt drift below
 * which we do no TSF adjustment.
 */
#define TOFFSET_MINIMUM_ADJUSTMENT 10

/* This is not in the standard. It is a margin added to the
 * Toffset setpoint to mitigate TSF overcorrection
 * introduced by TSF adjustment latency.
 */
#define TOFFSET_SET_MARGIN 20

/* This is not in the standard.  It represents the maximum Toffset jump above
 * which we'll invalidate the Toffset setpoint and choose a new setpoint.  This
 * could be, for instance, in case a neighbor is restarted and its TSF counter
 * reset.
 */
#define TOFFSET_MAXIMUM_ADJUSTMENT 30000        /* 30 ms */

struct sync_method {
    u8 method;
    struct ieee80211_mesh_sync_ops ops;
};

static bool mesh_peer_tbtt_adjusting(struct ieee802_11_elems *ie)
{
    return (ie->mesh_config->meshconf_cap &
        MESHCONF_CAPAB_TBTT_ADJUSTING) != 0;
}

void mesh_sync_adjust_tbtt(struct ieee80211_sub_if_data *sdata)
{
    struct ieee80211_local *local = sdata->local;
    struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
    /* sdata->vif.bss_conf.beacon_int in 1024us units, 0.04% */
    u64 beacon_int_fraction = sdata->vif.bss_conf.beacon_int * 1024 / 2500;
    u64 tsf;
    u64 tsfdelta;

    spin_lock_bh(&ifmsh->sync_offset_lock);
    if (ifmsh->sync_offset_clockdrift_max < beacon_int_fraction) {
        msync_dbg(sdata, "TBTT : max clockdrift=%lld; adjusting\n",
              (long long) ifmsh->sync_offset_clockdrift_max);
        tsfdelta = -ifmsh->sync_offset_clockdrift_max;
        ifmsh->sync_offset_clockdrift_max = 0;
    } else {
        msync_dbg(sdata, "TBTT : max clockdrift=%lld; adjusting by %llu\n",
              (long long) ifmsh->sync_offset_clockdrift_max,
              (unsigned long long) beacon_int_fraction);
        tsfdelta = -beacon_int_fraction;
        ifmsh->sync_offset_clockdrift_max -= beacon_int_fraction;
    }
    spin_unlock_bh(&ifmsh->sync_offset_lock);

    tsf = drv_get_tsf(local, sdata);
    if (tsf != -1ULL)
        drv_set_tsf(local, sdata, tsf + tsfdelta);
}

static void mesh_sync_offset_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)
{
    struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
    struct ieee80211_local *local = sdata->local;
    struct sta_info *sta;
    u64 t_t, t_r;

    WARN_ON(ifmsh->mesh_sp_id != IEEE80211_SYNC_METHOD_NEIGHBOR_OFFSET);

    /* standard mentions only beacons */
    if (stype != IEEE80211_STYPE_BEACON)
        return;

    /* The current tsf is a first approximation for the timestamp
     * for the received beacon.  Further down we try to get a
     * better value from the rx_status->mactime field if
     * available. Also we have to call drv_get_tsf() before
     * entering the rcu-read section.*/
    t_r = drv_get_tsf(local, sdata);

    rcu_read_lock();
    sta = sta_info_get(sdata, mgmt->sa);
    if (!sta)
        goto no_sync;

    /* check offset sync conditions (13.13.2.2.1)
     *
     * TODO also sync to
     * dot11MeshNbrOffsetMaxNeighbor non-peer non-MBSS neighbors
     */

    if (elems->mesh_config && mesh_peer_tbtt_adjusting(elems)) {
        clear_sta_flag(sta, WLAN_STA_TOFFSET_KNOWN);
        msync_dbg(sdata, "STA %pM : is adjusting TBTT\n", sta->sta.addr);
        goto no_sync;
    }

    if (rx_status->flag & RX_FLAG_MACTIME_MPDU && rx_status->mactime) {
        /*
         * The mactime is defined as the time the first data symbol
         * of the frame hits the PHY, and the timestamp of the beacon
         * is defined as "the time that the data symbol containing the
         * first bit of the timestamp is transmitted to the PHY plus
         * the transmitting STA's delays through its local PHY from the
         * MAC-PHY interface to its interface with the WM" (802.11
         * 11.1.2)
         *
         * T_r, in 13.13.2.2.2, is just defined as "the frame reception
         * time" but we unless we interpret that time to be the same
         * time of the beacon timestamp, the offset calculation will be
         * off.  Below we adjust t_r to be "the time at which the first
         * symbol of the timestamp element in the beacon is received".
         * This correction depends on the rate.
         *
         * Based on similar code in ibss.c
         */
        int rate;

        if (rx_status->flag & RX_FLAG_HT) {
            /* TODO:
             * In principle there could be HT-beacons (Dual Beacon
             * HT Operation options), but for now ignore them and
             * just use the primary (i.e. non-HT) beacons for
             * synchronization.
             * */
            goto no_sync;
        } else
            rate = local->hw.wiphy->bands[rx_status->band]->
                bitrates[rx_status->rate_idx].bitrate;

        /* 24 bytes of header * 8 bits/byte *
         * 10*(100 Kbps)/Mbps / rate (100 Kbps)*/
        t_r = rx_status->mactime + (24 * 8 * 10 / rate);
    }

    /* Timing offset calculation (see 13.13.2.2.2) */
    t_t = le64_to_cpu(mgmt->u.beacon.timestamp);
    sta->t_offset = t_t - t_r;

    if (test_sta_flag(sta, WLAN_STA_TOFFSET_KNOWN)) {
        s64 t_clockdrift = sta->t_offset_setpoint
                   - sta->t_offset;
        msync_dbg(sdata,
              "STA %pM : sta->t_offset=%lld, sta->t_offset_setpoint=%lld, t_clockdrift=%lld\n",
              sta->sta.addr,
              (long long) sta->t_offset,
              (long long)
              sta->t_offset_setpoint,
              (long long) t_clockdrift);

        if (t_clockdrift > TOFFSET_MAXIMUM_ADJUSTMENT ||
            t_clockdrift < -TOFFSET_MAXIMUM_ADJUSTMENT) {
            msync_dbg(sdata,
                  "STA %pM : t_clockdrift=%lld too large, setpoint reset\n",
                  sta->sta.addr,
                  (long long) t_clockdrift);
            clear_sta_flag(sta, WLAN_STA_TOFFSET_KNOWN);
            goto no_sync;
        }

        rcu_read_unlock();

        spin_lock_bh(&ifmsh->sync_offset_lock);
        if (t_clockdrift >
            ifmsh->sync_offset_clockdrift_max)
            ifmsh->sync_offset_clockdrift_max
                = t_clockdrift;
        spin_unlock_bh(&ifmsh->sync_offset_lock);

    } else {
        sta->t_offset_setpoint = sta->t_offset - TOFFSET_SET_MARGIN;
        set_sta_flag(sta, WLAN_STA_TOFFSET_KNOWN);
        msync_dbg(sdata,
              "STA %pM : offset was invalid, sta->t_offset=%lld\n",
              sta->sta.addr,
              (long long) sta->t_offset);
        rcu_read_unlock();
    }
    return;

no_sync:
    rcu_read_unlock();
}

static void mesh_sync_offset_adjust_tbtt(struct ieee80211_sub_if_data *sdata)
{
    struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;

    WARN_ON(ifmsh->mesh_sp_id
        != IEEE80211_SYNC_METHOD_NEIGHBOR_OFFSET);
    BUG_ON(!rcu_read_lock_held());

    spin_lock_bh(&ifmsh->sync_offset_lock);

    if (ifmsh->sync_offset_clockdrift_max >
        TOFFSET_MINIMUM_ADJUSTMENT) {
        /* Since ajusting the tsf here would
         * require a possibly blocking call
         * to the driver tsf setter, we punt
         * the tsf adjustment to the mesh tasklet
         */
        msync_dbg(sdata,
              "TBTT : kicking off TBTT adjustment with clockdrift_max=%lld\n",
              ifmsh->sync_offset_clockdrift_max);
        set_bit(MESH_WORK_DRIFT_ADJUST,
            &ifmsh->wrkq_flags);
    } else {
        msync_dbg(sdata,
              "TBTT : max clockdrift=%lld; too small to adjust\n",
              (long long)ifmsh->sync_offset_clockdrift_max);
        ifmsh->sync_offset_clockdrift_max = 0;
    }
    spin_unlock_bh(&ifmsh->sync_offset_lock);
}

static const u8 *mesh_get_vendor_oui(struct ieee80211_sub_if_data *sdata)
{
    struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
    u8 offset;

    if (!ifmsh->ie || !ifmsh->ie_len)
        return NULL;

    offset = ieee80211_ie_split_vendor(ifmsh->ie,
                    ifmsh->ie_len, 0);

    if (!offset)
        return NULL;

    return ifmsh->ie + offset + 2;
}

static void mesh_sync_vendor_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)
{
    const u8 *oui;

    WARN_ON(sdata->u.mesh.mesh_sp_id != IEEE80211_SYNC_METHOD_VENDOR);
    msync_dbg(sdata, "called mesh_sync_vendor_rx_bcn_presp\n");
    oui = mesh_get_vendor_oui(sdata);
    /*  here you would implement the vendor offset tracking for this oui */
}

static void mesh_sync_vendor_adjust_tbtt(struct ieee80211_sub_if_data *sdata)
{
    const u8 *oui;

    WARN_ON(sdata->u.mesh.mesh_sp_id != IEEE80211_SYNC_METHOD_VENDOR);
    msync_dbg(sdata, "called mesh_sync_vendor_adjust_tbtt\n");
    oui = mesh_get_vendor_oui(sdata);
    /*  here you would implement the vendor tsf adjustment for this oui */
}

/* global variable */
static struct sync_method sync_methods[] = {
    {
        .method = IEEE80211_SYNC_METHOD_NEIGHBOR_OFFSET,
        .ops = {
            .rx_bcn_presp = &mesh_sync_offset_rx_bcn_presp,
            .adjust_tbtt = &mesh_sync_offset_adjust_tbtt,
        }
    },
    {
        .method = IEEE80211_SYNC_METHOD_VENDOR,
        .ops = {
            .rx_bcn_presp = &mesh_sync_vendor_rx_bcn_presp,
            .adjust_tbtt = &mesh_sync_vendor_adjust_tbtt,
        }
    },
};

struct ieee80211_mesh_sync_ops *ieee80211_mesh_sync_ops_get(u8 method)
{
    struct ieee80211_mesh_sync_ops *ops = NULL;
    u8 i;

    for (i = 0 ; i < ARRAY_SIZE(sync_methods); ++i) {
        if (sync_methods[i].method == method) {
            ops = &sync_methods[i].ops;
            break;
        }
    }
    return ops;
}