mesh_sync.c

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/*
 * Copyright 2011-2012, Pavel Zubarev <pavel.zubarev@gmail.com>
 * Copyright 2011-2012, Marco Porsch <marco.porsch@s2005.tu-chemnitz.de>
 * 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"

#ifdef CONFIG_MAC80211_VERBOSE_MESH_SYNC_DEBUG
#define msync_dbg(fmt, args...) \
        printk(KERN_DEBUG "Mesh sync (%s): " fmt "\n", sdata->name, ##args)
#else
#define msync_dbg(fmt, args...)   do { (void)(0); } while (0)
#endif

/* 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("TBTT : max clockdrift=%lld; adjusting",
                        (long long) ifmsh->sync_offset_clockdrift_max);
                tsfdelta = -ifmsh->sync_offset_clockdrift_max;
                ifmsh->sync_offset_clockdrift_max = 0;
        } else {
                msync_dbg("TBTT : max clockdrift=%lld; adjusting by %llu",
                        (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;
        }

        tsf = drv_get_tsf(local, sdata);
        if (tsf != -1ULL)
                drv_set_tsf(local, sdata, tsf + tsfdelta);
        spin_unlock_bh(&ifmsh->sync_offset_lock);
}

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("STA %pM : is adjusting TBTT", 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("STA %pM : sta->t_offset=%lld, sta->t_offset_setpoint=%lld, t_clockdrift=%lld",
                          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("STA %pM : t_clockdrift=%lld too large, setpoint reset",
                                  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("STA %pM : offset was invalid, "
                          " sta->t_offset=%lld",
                          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("TBTT : kicking off TBTT "
                          "adjustment with "
                          "clockdrift_max=%lld",
                  ifmsh->sync_offset_clockdrift_max);
                set_bit(MESH_WORK_DRIFT_ADJUST,
                        &ifmsh->wrkq_flags);
        } else {
                msync_dbg("TBTT : max clockdrift=%lld; "
                          "too small to adjust",
                          (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("called mesh_sync_vendor_rx_bcn_presp");
        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("called mesh_sync_vendor_adjust_tbtt");
        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;
}