/*
 * 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"

/* 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;
};

/**
 * mesh_peer_tbtt_adjusting - check if an mp is currently adjusting its TBTT
 *
 * @ie: information elements of a management frame from the mesh peer
 */
static bool mesh_peer_tbtt_adjusting(struct ieee802_11_elems *ie)
{
        return (ie->mesh_config->meshconf_cap &
                        IEEE80211_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;

        /*
         * Get time when timestamp field was received.  If we don't
         * have rx timestamps, then use current tsf as an approximation.
         * drv_get_tsf() must be called before entering the rcu-read
         * section.
         */
        if (ieee80211_have_rx_timestamp(rx_status))
                t_r = ieee80211_calculate_rx_timestamp(local, rx_status,
                                                       24 + 12 +
                                                       elems->total_len +
                                                       FCS_LEN,
                                                       24);
        else
                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;
        }

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

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

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

no_sync:
        rcu_read_unlock();
}

static void mesh_sync_offset_adjust_tbtt(struct ieee80211_sub_if_data *sdata,
                                         struct beacon_data *beacon)
{
        struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
        u8 cap;

        WARN_ON(ifmsh->mesh_sp_id != IEEE80211_SYNC_METHOD_NEIGHBOR_OFFSET);
        WARN_ON(!rcu_read_lock_held());
        cap = beacon->meshconf->meshconf_cap;

        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);

                ifmsh->adjusting_tbtt = true;
        } 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;

                ifmsh->adjusting_tbtt = false;
        }
        spin_unlock_bh(&ifmsh->sync_offset_lock);

        beacon->meshconf->meshconf_cap = ifmsh->adjusting_tbtt ?
                        IEEE80211_MESHCONF_CAPAB_TBTT_ADJUSTING | cap :
                        ~IEEE80211_MESHCONF_CAPAB_TBTT_ADJUSTING & cap;
}

static const 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,
                }
        },
};

const struct ieee80211_mesh_sync_ops *ieee80211_mesh_sync_ops_get(u8 method)
{
        int i;

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