/*
   * 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
  ",
  			  (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
  ",
  			  (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
  ",
  			  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->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
  ",
  			  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
  ",
  				  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->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
  ",
  			  sta->sta.addr,
  			  (long long) sta->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);
  	BUG_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
  ",
  			  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
  ",
  			  (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;
  }