/*
   * Copyright (C) 2010 Felix Fietkau <nbd@openwrt.org>
   *
   * 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 <linux/netdevice.h>
  #include <linux/types.h>
  #include <linux/skbuff.h>
  #include <linux/debugfs.h>
  #include <linux/random.h>
  #include <linux/ieee80211.h>
  #include <net/mac80211.h>
  #include "rate.h"
  #include "rc80211_minstrel.h"
  #include "rc80211_minstrel_ht.h"
  
  #define AVG_PKT_SIZE	1200
  #define SAMPLE_COLUMNS	10
  #define EWMA_LEVEL		75
  
  /* Number of bits for an average sized packet */
  #define MCS_NBITS (AVG_PKT_SIZE << 3)
  
  /* Number of symbols for a packet with (bps) bits per symbol */
  #define MCS_NSYMS(bps) ((MCS_NBITS + (bps) - 1) / (bps))
  
  /* Transmission time for a packet containing (syms) symbols */
  #define MCS_SYMBOL_TIME(sgi, syms)					\
  	(sgi ?								\
  	  ((syms) * 18 + 4) / 5 :	/* syms * 3.6 us */		\
  	  (syms) << 2			/* syms * 4 us */		\
  	)
  
  /* Transmit duration for the raw data part of an average sized packet */
  #define MCS_DURATION(streams, sgi, bps) MCS_SYMBOL_TIME(sgi, MCS_NSYMS((streams) * (bps)))

  /*
   * Define group sort order: HT40 -> SGI -> #streams
   */
  #define GROUP_IDX(_streams, _sgi, _ht40)	\
  	MINSTREL_MAX_STREAMS * 2 * _ht40 +	\
  	MINSTREL_MAX_STREAMS * _sgi +		\
  	_streams - 1

  /* MCS rate information for an MCS group */

  #define MCS_GROUP(_streams, _sgi, _ht40)				\
  	[GROUP_IDX(_streams, _sgi, _ht40)] = {				\

  	.streams = _streams,						\
  	.flags =							\
  		(_sgi ? IEEE80211_TX_RC_SHORT_GI : 0) |			\
  		(_ht40 ? IEEE80211_TX_RC_40_MHZ_WIDTH : 0),		\
  	.duration = {							\
  		MCS_DURATION(_streams, _sgi, _ht40 ? 54 : 26),		\
  		MCS_DURATION(_streams, _sgi, _ht40 ? 108 : 52),		\
  		MCS_DURATION(_streams, _sgi, _ht40 ? 162 : 78),		\
  		MCS_DURATION(_streams, _sgi, _ht40 ? 216 : 104),	\
  		MCS_DURATION(_streams, _sgi, _ht40 ? 324 : 156),	\
  		MCS_DURATION(_streams, _sgi, _ht40 ? 432 : 208),	\
  		MCS_DURATION(_streams, _sgi, _ht40 ? 486 : 234),	\
  		MCS_DURATION(_streams, _sgi, _ht40 ? 540 : 260)		\
  	}								\
  }
  
  /*
   * To enable sufficiently targeted rate sampling, MCS rates are divided into
   * groups, based on the number of streams and flags (HT40, SGI) that they
   * use.

   *
   * Sortorder has to be fixed for GROUP_IDX macro to be applicable:
   * HT40 -> SGI -> #streams

   */
  const struct mcs_group minstrel_mcs_groups[] = {
  	MCS_GROUP(1, 0, 0),
  	MCS_GROUP(2, 0, 0),
  #if MINSTREL_MAX_STREAMS >= 3
  	MCS_GROUP(3, 0, 0),
  #endif
  
  	MCS_GROUP(1, 1, 0),
  	MCS_GROUP(2, 1, 0),
  #if MINSTREL_MAX_STREAMS >= 3
  	MCS_GROUP(3, 1, 0),
  #endif
  
  	MCS_GROUP(1, 0, 1),
  	MCS_GROUP(2, 0, 1),
  #if MINSTREL_MAX_STREAMS >= 3
  	MCS_GROUP(3, 0, 1),
  #endif
  
  	MCS_GROUP(1, 1, 1),
  	MCS_GROUP(2, 1, 1),
  #if MINSTREL_MAX_STREAMS >= 3
  	MCS_GROUP(3, 1, 1),
  #endif
  };
  
  static u8 sample_table[SAMPLE_COLUMNS][MCS_GROUP_RATES];
  
  /*
   * Perform EWMA (Exponentially Weighted Moving Average) calculation
   */
  static int
  minstrel_ewma(int old, int new, int weight)
  {
  	return (new * (100 - weight) + old * weight) / 100;
  }
  
  /*
   * Look up an MCS group index based on mac80211 rate information
   */
  static int
  minstrel_ht_get_group_idx(struct ieee80211_tx_rate *rate)
  {

  	return GROUP_IDX((rate->idx / MCS_GROUP_RATES) + 1,
  			 !!(rate->flags & IEEE80211_TX_RC_SHORT_GI),
  			 !!(rate->flags & IEEE80211_TX_RC_40_MHZ_WIDTH));

  }
  
  static inline struct minstrel_rate_stats *
  minstrel_get_ratestats(struct minstrel_ht_sta *mi, int index)
  {
  	return &mi->groups[index / MCS_GROUP_RATES].rates[index % MCS_GROUP_RATES];
  }
  
  
  /*
   * Recalculate success probabilities and counters for a rate using EWMA
   */
  static void

  minstrel_calc_rate_ewma(struct minstrel_rate_stats *mr)

  {
  	if (unlikely(mr->attempts > 0)) {
  		mr->sample_skipped = 0;
  		mr->cur_prob = MINSTREL_FRAC(mr->success, mr->attempts);
  		if (!mr->att_hist)
  			mr->probability = mr->cur_prob;
  		else
  			mr->probability = minstrel_ewma(mr->probability,
  				mr->cur_prob, EWMA_LEVEL);
  		mr->att_hist += mr->attempts;
  		mr->succ_hist += mr->success;
  	} else {
  		mr->sample_skipped++;
  	}
  	mr->last_success = mr->success;
  	mr->last_attempts = mr->attempts;
  	mr->success = 0;
  	mr->attempts = 0;
  }
  
  /*
   * Calculate throughput based on the average A-MPDU length, taking into account
   * the expected number of retransmissions and their expected length
   */
  static void

  minstrel_ht_calc_tp(struct minstrel_ht_sta *mi, int group, int rate)

  {
  	struct minstrel_rate_stats *mr;
  	unsigned int usecs;
  
  	mr = &mi->groups[group].rates[rate];
  
  	if (mr->probability < MINSTREL_FRAC(1, 10)) {
  		mr->cur_tp = 0;
  		return;
  	}
  
  	usecs = mi->overhead / MINSTREL_TRUNC(mi->avg_ampdu_len);
  	usecs += minstrel_mcs_groups[group].duration[rate];
  	mr->cur_tp = MINSTREL_TRUNC((1000000 / usecs) * mr->probability);
  }
  
  /*
   * Update rate statistics and select new primary rates
   *
   * Rules for rate selection:
   *  - max_prob_rate must use only one stream, as a tradeoff between delivery
   *    probability and throughput during strong fluctuations
   *  - as long as the max prob rate has a probability of more than 3/4, pick
   *    higher throughput rates, even if the probablity is a bit lower
   */
  static void
  minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
  {
  	struct minstrel_mcs_group_data *mg;
  	struct minstrel_rate_stats *mr;
  	int cur_prob, cur_prob_tp, cur_tp, cur_tp2;
  	int group, i, index;
  
  	if (mi->ampdu_packets > 0) {
  		mi->avg_ampdu_len = minstrel_ewma(mi->avg_ampdu_len,
  			MINSTREL_FRAC(mi->ampdu_len, mi->ampdu_packets), EWMA_LEVEL);
  		mi->ampdu_len = 0;
  		mi->ampdu_packets = 0;
  	}
  
  	mi->sample_slow = 0;
  	mi->sample_count = 0;
  	mi->max_tp_rate = 0;
  	mi->max_tp_rate2 = 0;
  	mi->max_prob_rate = 0;
  
  	for (group = 0; group < ARRAY_SIZE(minstrel_mcs_groups); group++) {
  		cur_prob = 0;
  		cur_prob_tp = 0;
  		cur_tp = 0;
  		cur_tp2 = 0;
  
  		mg = &mi->groups[group];
  		if (!mg->supported)
  			continue;
  
  		mg->max_tp_rate = 0;
  		mg->max_tp_rate2 = 0;
  		mg->max_prob_rate = 0;
  		mi->sample_count++;
  
  		for (i = 0; i < MCS_GROUP_RATES; i++) {
  			if (!(mg->supported & BIT(i)))
  				continue;
  
  			mr = &mg->rates[i];
  			mr->retry_updated = false;
  			index = MCS_GROUP_RATES * group + i;

  			minstrel_calc_rate_ewma(mr);
  			minstrel_ht_calc_tp(mi, group, i);

  
  			if (!mr->cur_tp)
  				continue;
  
  			/* ignore the lowest rate of each single-stream group */
  			if (!i && minstrel_mcs_groups[group].streams == 1)
  				continue;
  
  			if ((mr->cur_tp > cur_prob_tp && mr->probability >
  			     MINSTREL_FRAC(3, 4)) || mr->probability > cur_prob) {
  				mg->max_prob_rate = index;
  				cur_prob = mr->probability;

  				cur_prob_tp = mr->cur_tp;

  			}
  
  			if (mr->cur_tp > cur_tp) {
  				swap(index, mg->max_tp_rate);
  				cur_tp = mr->cur_tp;
  				mr = minstrel_get_ratestats(mi, index);
  			}
  
  			if (index >= mg->max_tp_rate)
  				continue;
  
  			if (mr->cur_tp > cur_tp2) {
  				mg->max_tp_rate2 = index;
  				cur_tp2 = mr->cur_tp;
  			}
  		}
  	}

  	/* try to sample up to half of the available rates during each interval */

  	mi->sample_count *= 4;
  
  	cur_prob = 0;
  	cur_prob_tp = 0;
  	cur_tp = 0;
  	cur_tp2 = 0;
  	for (group = 0; group < ARRAY_SIZE(minstrel_mcs_groups); group++) {
  		mg = &mi->groups[group];
  		if (!mg->supported)
  			continue;
  
  		mr = minstrel_get_ratestats(mi, mg->max_prob_rate);
  		if (cur_prob_tp < mr->cur_tp &&
  		    minstrel_mcs_groups[group].streams == 1) {
  			mi->max_prob_rate = mg->max_prob_rate;
  			cur_prob = mr->cur_prob;

  			cur_prob_tp = mr->cur_tp;

  		}
  
  		mr = minstrel_get_ratestats(mi, mg->max_tp_rate);
  		if (cur_tp < mr->cur_tp) {

  			mi->max_tp_rate2 = mi->max_tp_rate;
  			cur_tp2 = cur_tp;

  			mi->max_tp_rate = mg->max_tp_rate;
  			cur_tp = mr->cur_tp;
  		}
  
  		mr = minstrel_get_ratestats(mi, mg->max_tp_rate2);
  		if (cur_tp2 < mr->cur_tp) {
  			mi->max_tp_rate2 = mg->max_tp_rate2;
  			cur_tp2 = mr->cur_tp;
  		}
  	}
  
  	mi->stats_update = jiffies;
  }
  
  static bool
  minstrel_ht_txstat_valid(struct ieee80211_tx_rate *rate)
  {

  	if (rate->idx < 0)

  		return false;

  	if (!rate->count)

  		return false;
  
  	return !!(rate->flags & IEEE80211_TX_RC_MCS);
  }
  
  static void
  minstrel_next_sample_idx(struct minstrel_ht_sta *mi)
  {
  	struct minstrel_mcs_group_data *mg;
  
  	for (;;) {
  		mi->sample_group++;
  		mi->sample_group %= ARRAY_SIZE(minstrel_mcs_groups);
  		mg = &mi->groups[mi->sample_group];
  
  		if (!mg->supported)
  			continue;
  
  		if (++mg->index >= MCS_GROUP_RATES) {
  			mg->index = 0;
  			if (++mg->column >= ARRAY_SIZE(sample_table))
  				mg->column = 0;
  		}
  		break;
  	}
  }
  
  static void

  minstrel_downgrade_rate(struct minstrel_ht_sta *mi, unsigned int *idx,
  			bool primary)

  {
  	int group, orig_group;
  
  	orig_group = group = *idx / MCS_GROUP_RATES;
  	while (group > 0) {
  		group--;
  
  		if (!mi->groups[group].supported)
  			continue;
  
  		if (minstrel_mcs_groups[group].streams >
  		    minstrel_mcs_groups[orig_group].streams)
  			continue;
  
  		if (primary)
  			*idx = mi->groups[group].max_tp_rate;
  		else
  			*idx = mi->groups[group].max_tp_rate2;
  		break;
  	}
  }
  
  static void

  minstrel_aggr_check(struct ieee80211_sta *pubsta, struct sk_buff *skb)

  {
  	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
  	struct sta_info *sta = container_of(pubsta, struct sta_info, sta);
  	u16 tid;
  
  	if (unlikely(!ieee80211_is_data_qos(hdr->frame_control)))
  		return;
  
  	if (unlikely(skb->protocol == cpu_to_be16(ETH_P_PAE)))
  		return;
  
  	tid = *ieee80211_get_qos_ctl(hdr) & IEEE80211_QOS_CTL_TID_MASK;

  	if (likely(sta->ampdu_mlme.tid_tx[tid]))

  		return;

  	if (skb_get_queue_mapping(skb) == IEEE80211_AC_VO)
  		return;

  	ieee80211_start_tx_ba_session(pubsta, tid, 5000);

  }
  
  static void
  minstrel_ht_tx_status(void *priv, struct ieee80211_supported_band *sband,
                        struct ieee80211_sta *sta, void *priv_sta,
                        struct sk_buff *skb)
  {
  	struct minstrel_ht_sta_priv *msp = priv_sta;
  	struct minstrel_ht_sta *mi = &msp->ht;
  	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
  	struct ieee80211_tx_rate *ar = info->status.rates;
  	struct minstrel_rate_stats *rate, *rate2;
  	struct minstrel_priv *mp = priv;
  	bool last = false;
  	int group;
  	int i = 0;
  
  	if (!msp->is_ht)
  		return mac80211_minstrel.tx_status(priv, sband, sta, &msp->legacy, skb);
  
  	/* This packet was aggregated but doesn't carry status info */
  	if ((info->flags & IEEE80211_TX_CTL_AMPDU) &&
  	    !(info->flags & IEEE80211_TX_STAT_AMPDU))
  		return;

  	if (!(info->flags & IEEE80211_TX_STAT_AMPDU)) {
  		info->status.ampdu_ack_len =
  			(info->flags & IEEE80211_TX_STAT_ACK ? 1 : 0);

  		info->status.ampdu_len = 1;
  	}
  
  	mi->ampdu_packets++;
  	mi->ampdu_len += info->status.ampdu_len;
  
  	if (!mi->sample_wait && !mi->sample_tries && mi->sample_count > 0) {

  		mi->sample_wait = 16 + 2 * MINSTREL_TRUNC(mi->avg_ampdu_len);
  		mi->sample_tries = 2;

  		mi->sample_count--;
  	}

  	if (info->flags & IEEE80211_TX_CTL_RATE_CTRL_PROBE)

  		mi->sample_packets += info->status.ampdu_len;

  
  	for (i = 0; !last; i++) {
  		last = (i == IEEE80211_TX_MAX_RATES - 1) ||
  		       !minstrel_ht_txstat_valid(&ar[i + 1]);
  
  		if (!minstrel_ht_txstat_valid(&ar[i]))
  			break;
  
  		group = minstrel_ht_get_group_idx(&ar[i]);
  		rate = &mi->groups[group].rates[ar[i].idx % 8];

  		if (last)

  			rate->success += info->status.ampdu_ack_len;
  
  		rate->attempts += ar[i].count * info->status.ampdu_len;
  	}
  
  	/*
  	 * check for sudden death of spatial multiplexing,
  	 * downgrade to a lower number of streams if necessary.
  	 */
  	rate = minstrel_get_ratestats(mi, mi->max_tp_rate);
  	if (rate->attempts > 30 &&
  	    MINSTREL_FRAC(rate->success, rate->attempts) <
  	    MINSTREL_FRAC(20, 100))
  		minstrel_downgrade_rate(mi, &mi->max_tp_rate, true);
  
  	rate2 = minstrel_get_ratestats(mi, mi->max_tp_rate2);

  	if (rate2->attempts > 30 &&
  	    MINSTREL_FRAC(rate2->success, rate2->attempts) <

  	    MINSTREL_FRAC(20, 100))
  		minstrel_downgrade_rate(mi, &mi->max_tp_rate2, false);
  
  	if (time_after(jiffies, mi->stats_update + (mp->update_interval / 2 * HZ) / 1000)) {
  		minstrel_ht_update_stats(mp, mi);

  		if (!(info->flags & IEEE80211_TX_CTL_AMPDU))

  			minstrel_aggr_check(sta, skb);

  	}
  }
  
  static void
  minstrel_calc_retransmit(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
                           int index)
  {
  	struct minstrel_rate_stats *mr;
  	const struct mcs_group *group;
  	unsigned int tx_time, tx_time_rtscts, tx_time_data;
  	unsigned int cw = mp->cw_min;

  	unsigned int ctime = 0;

  	unsigned int t_slot = 9; /* FIXME */
  	unsigned int ampdu_len = MINSTREL_TRUNC(mi->avg_ampdu_len);
  
  	mr = minstrel_get_ratestats(mi, index);
  	if (mr->probability < MINSTREL_FRAC(1, 10)) {
  		mr->retry_count = 1;
  		mr->retry_count_rtscts = 1;
  		return;
  	}
  
  	mr->retry_count = 2;
  	mr->retry_count_rtscts = 2;
  	mr->retry_updated = true;
  
  	group = &minstrel_mcs_groups[index / MCS_GROUP_RATES];
  	tx_time_data = group->duration[index % MCS_GROUP_RATES] * ampdu_len;

  
  	/* Contention time for first 2 tries */
  	ctime = (t_slot * cw) >> 1;
  	cw = min((cw << 1) | 1, mp->cw_max);
  	ctime += (t_slot * cw) >> 1;
  	cw = min((cw << 1) | 1, mp->cw_max);
  
  	/* Total TX time for data and Contention after first 2 tries */
  	tx_time = ctime + 2 * (mi->overhead + tx_time_data);
  	tx_time_rtscts = ctime + 2 * (mi->overhead_rtscts + tx_time_data);
  
  	/* See how many more tries we can fit inside segment size */

  	do {

  		/* Contention time for this try */
  		ctime = (t_slot * cw) >> 1;
  		cw = min((cw << 1) | 1, mp->cw_max);
  
  		/* Total TX time after this try */
  		tx_time += ctime + mi->overhead + tx_time_data;
  		tx_time_rtscts += ctime + mi->overhead_rtscts + tx_time_data;

  		if (tx_time_rtscts < mp->segment_size)
  			mr->retry_count_rtscts++;
  	} while ((tx_time < mp->segment_size) &&
  	         (++mr->retry_count < mp->max_retry));
  }
  
  
  static void
  minstrel_ht_set_rate(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
                       struct ieee80211_tx_rate *rate, int index,

                       bool sample, bool rtscts)
  {
  	const struct mcs_group *group = &minstrel_mcs_groups[index / MCS_GROUP_RATES];
  	struct minstrel_rate_stats *mr;
  
  	mr = minstrel_get_ratestats(mi, index);
  	if (!mr->retry_updated)
  		minstrel_calc_retransmit(mp, mi, index);

  	if (sample)
  		rate->count = 1;
  	else if (mr->probability < MINSTREL_FRAC(20, 100))

  		rate->count = 2;
  	else if (rtscts)
  		rate->count = mr->retry_count_rtscts;
  	else
  		rate->count = mr->retry_count;
  
  	rate->flags = IEEE80211_TX_RC_MCS | group->flags;

  	if (rtscts)

  		rate->flags |= IEEE80211_TX_RC_USE_RTS_CTS;
  	rate->idx = index % MCS_GROUP_RATES + (group->streams - 1) * MCS_GROUP_RATES;
  }
  
  static inline int
  minstrel_get_duration(int index)
  {
  	const struct mcs_group *group = &minstrel_mcs_groups[index / MCS_GROUP_RATES];
  	return group->duration[index % MCS_GROUP_RATES];
  }
  
  static int
  minstrel_get_sample_rate(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
  {
  	struct minstrel_rate_stats *mr;
  	struct minstrel_mcs_group_data *mg;
  	int sample_idx = 0;
  
  	if (mi->sample_wait > 0) {
  		mi->sample_wait--;
  		return -1;
  	}
  
  	if (!mi->sample_tries)
  		return -1;
  
  	mi->sample_tries--;
  	mg = &mi->groups[mi->sample_group];
  	sample_idx = sample_table[mg->column][mg->index];
  	mr = &mg->rates[sample_idx];
  	sample_idx += mi->sample_group * MCS_GROUP_RATES;

  	minstrel_next_sample_idx(mi);

  
  	/*
  	 * When not using MRR, do not sample if the probability is already
  	 * higher than 95% to avoid wasting airtime
  	 */
  	if (!mp->has_mrr && (mr->probability > MINSTREL_FRAC(95, 100)))

  		return -1;

  
  	/*
  	 * Make sure that lower rates get sampled only occasionally,
  	 * if the link is working perfectly.
  	 */
  	if (minstrel_get_duration(sample_idx) >
  	    minstrel_get_duration(mi->max_tp_rate)) {

  		if (mr->sample_skipped < 20)

  			return -1;

  
  		if (mi->sample_slow++ > 2)

  			return -1;

  	}
  
  	return sample_idx;

  }
  
  static void
  minstrel_ht_get_rate(void *priv, struct ieee80211_sta *sta, void *priv_sta,
                       struct ieee80211_tx_rate_control *txrc)
  {
  	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(txrc->skb);
  	struct ieee80211_tx_rate *ar = info->status.rates;
  	struct minstrel_ht_sta_priv *msp = priv_sta;
  	struct minstrel_ht_sta *mi = &msp->ht;
  	struct minstrel_priv *mp = priv;
  	int sample_idx;

  	bool sample = false;

  
  	if (rate_control_send_low(sta, priv_sta, txrc))
  		return;
  
  	if (!msp->is_ht)
  		return mac80211_minstrel.get_rate(priv, sta, &msp->legacy, txrc);
  
  	info->flags |= mi->tx_flags;

  
  	/* Don't use EAPOL frames for sampling on non-mrr hw */
  	if (mp->hw->max_rates == 1 &&
  	    txrc->skb->protocol == cpu_to_be16(ETH_P_PAE))
  		sample_idx = -1;
  	else
  		sample_idx = minstrel_get_sample_rate(mp, mi);

  
  #ifdef CONFIG_MAC80211_DEBUGFS
  	/* use fixed index if set */
  	if (mp->fixed_rate_idx != -1)
  		sample_idx = mp->fixed_rate_idx;
  #endif

  	if (sample_idx >= 0) {

  		sample = true;

  		minstrel_ht_set_rate(mp, mi, &ar[0], sample_idx,

  			true, false);

  		info->flags |= IEEE80211_TX_CTL_RATE_CTRL_PROBE;
  	} else {
  		minstrel_ht_set_rate(mp, mi, &ar[0], mi->max_tp_rate,

  			false, false);

  	}

  	if (mp->hw->max_rates >= 3) {
  		/*
  		 * At least 3 tx rates supported, use
  		 * sample_rate -> max_tp_rate -> max_prob_rate for sampling and
  		 * max_tp_rate -> max_tp_rate2 -> max_prob_rate by default.
  		 */
  		if (sample_idx >= 0)
  			minstrel_ht_set_rate(mp, mi, &ar[1], mi->max_tp_rate,

  				false, false);

  		else
  			minstrel_ht_set_rate(mp, mi, &ar[1], mi->max_tp_rate2,

  				false, true);

  
  		minstrel_ht_set_rate(mp, mi, &ar[2], mi->max_prob_rate,

  				     false, !sample);

  
  		ar[3].count = 0;
  		ar[3].idx = -1;
  	} else if (mp->hw->max_rates == 2) {
  		/*
  		 * Only 2 tx rates supported, use
  		 * sample_rate -> max_prob_rate for sampling and
  		 * max_tp_rate -> max_prob_rate by default.
  		 */
  		minstrel_ht_set_rate(mp, mi, &ar[1], mi->max_prob_rate,

  				     false, !sample);

  
  		ar[2].count = 0;
  		ar[2].idx = -1;
  	} else {
  		/* Not using MRR, only use the first rate */
  		ar[1].count = 0;
  		ar[1].idx = -1;
  	}

  
  	mi->total_packets++;
  
  	/* wraparound */
  	if (mi->total_packets == ~0) {
  		mi->total_packets = 0;
  		mi->sample_packets = 0;
  	}
  }
  
  static void
  minstrel_ht_update_caps(void *priv, struct ieee80211_supported_band *sband,
                          struct ieee80211_sta *sta, void *priv_sta,
  			enum nl80211_channel_type oper_chan_type)
  {
  	struct minstrel_priv *mp = priv;
  	struct minstrel_ht_sta_priv *msp = priv_sta;
  	struct minstrel_ht_sta *mi = &msp->ht;
  	struct ieee80211_mcs_info *mcs = &sta->ht_cap.mcs;
  	struct ieee80211_local *local = hw_to_local(mp->hw);
  	u16 sta_cap = sta->ht_cap.cap;

  	int n_supported = 0;

  	int ack_dur;
  	int stbc;
  	int i;
  
  	/* fall back to the old minstrel for legacy stations */

  	if (!sta->ht_cap.ht_supported)
  		goto use_legacy;

  
  	BUILD_BUG_ON(ARRAY_SIZE(minstrel_mcs_groups) !=
  		MINSTREL_MAX_STREAMS * MINSTREL_STREAM_GROUPS);
  
  	msp->is_ht = true;
  	memset(mi, 0, sizeof(*mi));
  	mi->stats_update = jiffies;
  
  	ack_dur = ieee80211_frame_duration(local, 10, 60, 1, 1);
  	mi->overhead = ieee80211_frame_duration(local, 0, 60, 1, 1) + ack_dur;
  	mi->overhead_rtscts = mi->overhead + 2 * ack_dur;
  
  	mi->avg_ampdu_len = MINSTREL_FRAC(1, 1);
  
  	/* When using MRR, sample more on the first attempt, without delay */
  	if (mp->has_mrr) {
  		mi->sample_count = 16;
  		mi->sample_wait = 0;
  	} else {
  		mi->sample_count = 8;
  		mi->sample_wait = 8;
  	}
  	mi->sample_tries = 4;
  
  	stbc = (sta_cap & IEEE80211_HT_CAP_RX_STBC) >>
  		IEEE80211_HT_CAP_RX_STBC_SHIFT;
  	mi->tx_flags |= stbc << IEEE80211_TX_CTL_STBC_SHIFT;
  
  	if (sta_cap & IEEE80211_HT_CAP_LDPC_CODING)
  		mi->tx_flags |= IEEE80211_TX_CTL_LDPC;
  
  	if (oper_chan_type != NL80211_CHAN_HT40MINUS &&
  	    oper_chan_type != NL80211_CHAN_HT40PLUS)
  		sta_cap &= ~IEEE80211_HT_CAP_SUP_WIDTH_20_40;
  
  	for (i = 0; i < ARRAY_SIZE(mi->groups); i++) {
  		u16 req = 0;
  
  		mi->groups[i].supported = 0;
  		if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_SHORT_GI) {
  			if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_40_MHZ_WIDTH)
  				req |= IEEE80211_HT_CAP_SGI_40;
  			else
  				req |= IEEE80211_HT_CAP_SGI_20;
  		}
  
  		if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_40_MHZ_WIDTH)
  			req |= IEEE80211_HT_CAP_SUP_WIDTH_20_40;
  
  		if ((sta_cap & req) != req)
  			continue;
  
  		mi->groups[i].supported =
  			mcs->rx_mask[minstrel_mcs_groups[i].streams - 1];

  
  		if (mi->groups[i].supported)
  			n_supported++;

  	}

  
  	if (!n_supported)
  		goto use_legacy;
  
  	return;
  
  use_legacy:
  	msp->is_ht = false;
  	memset(&msp->legacy, 0, sizeof(msp->legacy));
  	msp->legacy.r = msp->ratelist;
  	msp->legacy.sample_table = msp->sample_table;
  	return mac80211_minstrel.rate_init(priv, sband, sta, &msp->legacy);

  }
  
  static void
  minstrel_ht_rate_init(void *priv, struct ieee80211_supported_band *sband,
                        struct ieee80211_sta *sta, void *priv_sta)
  {
  	struct minstrel_priv *mp = priv;
  
  	minstrel_ht_update_caps(priv, sband, sta, priv_sta, mp->hw->conf.channel_type);
  }
  
  static void
  minstrel_ht_rate_update(void *priv, struct ieee80211_supported_band *sband,
                          struct ieee80211_sta *sta, void *priv_sta,
                          u32 changed, enum nl80211_channel_type oper_chan_type)
  {
  	minstrel_ht_update_caps(priv, sband, sta, priv_sta, oper_chan_type);
  }
  
  static void *
  minstrel_ht_alloc_sta(void *priv, struct ieee80211_sta *sta, gfp_t gfp)
  {
  	struct ieee80211_supported_band *sband;
  	struct minstrel_ht_sta_priv *msp;
  	struct minstrel_priv *mp = priv;
  	struct ieee80211_hw *hw = mp->hw;
  	int max_rates = 0;
  	int i;
  
  	for (i = 0; i < IEEE80211_NUM_BANDS; i++) {
  		sband = hw->wiphy->bands[i];
  		if (sband && sband->n_bitrates > max_rates)
  			max_rates = sband->n_bitrates;
  	}
  
  	msp = kzalloc(sizeof(struct minstrel_ht_sta), gfp);
  	if (!msp)
  		return NULL;
  
  	msp->ratelist = kzalloc(sizeof(struct minstrel_rate) * max_rates, gfp);
  	if (!msp->ratelist)
  		goto error;
  
  	msp->sample_table = kmalloc(SAMPLE_COLUMNS * max_rates, gfp);
  	if (!msp->sample_table)
  		goto error1;
  
  	return msp;
  
  error1:

  	kfree(msp->ratelist);

  error:
  	kfree(msp);
  	return NULL;
  }
  
  static void
  minstrel_ht_free_sta(void *priv, struct ieee80211_sta *sta, void *priv_sta)
  {
  	struct minstrel_ht_sta_priv *msp = priv_sta;
  
  	kfree(msp->sample_table);
  	kfree(msp->ratelist);
  	kfree(msp);
  }
  
  static void *
  minstrel_ht_alloc(struct ieee80211_hw *hw, struct dentry *debugfsdir)
  {
  	return mac80211_minstrel.alloc(hw, debugfsdir);
  }
  
  static void
  minstrel_ht_free(void *priv)
  {
  	mac80211_minstrel.free(priv);
  }
  
  static struct rate_control_ops mac80211_minstrel_ht = {
  	.name = "minstrel_ht",
  	.tx_status = minstrel_ht_tx_status,
  	.get_rate = minstrel_ht_get_rate,
  	.rate_init = minstrel_ht_rate_init,
  	.rate_update = minstrel_ht_rate_update,
  	.alloc_sta = minstrel_ht_alloc_sta,
  	.free_sta = minstrel_ht_free_sta,
  	.alloc = minstrel_ht_alloc,
  	.free = minstrel_ht_free,
  #ifdef CONFIG_MAC80211_DEBUGFS
  	.add_sta_debugfs = minstrel_ht_add_sta_debugfs,
  	.remove_sta_debugfs = minstrel_ht_remove_sta_debugfs,
  #endif
  };
  
  
  static void
  init_sample_table(void)
  {
  	int col, i, new_idx;
  	u8 rnd[MCS_GROUP_RATES];
  
  	memset(sample_table, 0xff, sizeof(sample_table));
  	for (col = 0; col < SAMPLE_COLUMNS; col++) {
  		for (i = 0; i < MCS_GROUP_RATES; i++) {
  			get_random_bytes(rnd, sizeof(rnd));
  			new_idx = (i + rnd[i]) % MCS_GROUP_RATES;
  
  			while (sample_table[col][new_idx] != 0xff)
  				new_idx = (new_idx + 1) % MCS_GROUP_RATES;
  
  			sample_table[col][new_idx] = i;
  		}
  	}
  }
  
  int __init
  rc80211_minstrel_ht_init(void)
  {
  	init_sample_table();
  	return ieee80211_rate_control_register(&mac80211_minstrel_ht);
  }
  
  void
  rc80211_minstrel_ht_exit(void)
  {
  	ieee80211_rate_control_unregister(&mac80211_minstrel_ht);
  }