/*
   * Copyright (C) 2008 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.
   *
   * Based on minstrel.c:
   *   Copyright (C) 2005-2007 Derek Smithies <derek@indranet.co.nz>
   *   Sponsored by Indranet Technologies Ltd
   *
   * Based on sample.c:
   *   Copyright (c) 2005 John Bicket
   *   All rights reserved.
   *
   *   Redistribution and use in source and binary forms, with or without
   *   modification, are permitted provided that the following conditions
   *   are met:
   *   1. Redistributions of source code must retain the above copyright
   *      notice, this list of conditions and the following disclaimer,
   *      without modification.
   *   2. Redistributions in binary form must reproduce at minimum a disclaimer
   *      similar to the "NO WARRANTY" disclaimer below ("Disclaimer") and any
   *      redistribution must be conditioned upon including a substantially
   *      similar Disclaimer requirement for further binary redistribution.
   *   3. Neither the names of the above-listed copyright holders nor the names
   *      of any contributors may be used to endorse or promote products derived
   *      from this software without specific prior written permission.
   *
   *   Alternatively, this software may be distributed under the terms of the
   *   GNU General Public License ("GPL") version 2 as published by the Free
   *   Software Foundation.
   *
   *   NO WARRANTY
   *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   *   ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   *   LIMITED TO, THE IMPLIED WARRANTIES OF NONINFRINGEMENT, MERCHANTIBILITY
   *   AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
   *   THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY,
   *   OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   *   SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   *   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
   *   IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   *   ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
   *   THE POSSIBILITY OF SUCH DAMAGES.
   */
  #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 <linux/slab.h>

  #include <net/mac80211.h>
  #include "rate.h"
  #include "rc80211_minstrel.h"

  #define SAMPLE_TBL(_mi, _idx, _col) \
  		_mi->sample_table[(_idx * SAMPLE_COLUMNS) + _col]
  
  /* convert mac80211 rate index to local array index */
  static inline int
  rix_to_ndx(struct minstrel_sta_info *mi, int rix)
  {
  	int i = rix;
  	for (i = rix; i >= 0; i--)
  		if (mi->r[i].rix == rix)
  			break;

  	return i;
  }

  /* return current EMWA throughput */

  int minstrel_get_tp_avg(struct minstrel_rate *mr, int prob_ewma)

  {
  	int usecs;
  
  	usecs = mr->perfect_tx_time;
  	if (!usecs)
  		usecs = 1000000;
  
  	/* reset thr. below 10% success */
  	if (mr->stats.prob_ewma < MINSTREL_FRAC(10, 100))
  		return 0;

  
  	if (prob_ewma > MINSTREL_FRAC(90, 100))
  		return MINSTREL_TRUNC(100000 * (MINSTREL_FRAC(90, 100) / usecs));

  	else

  		return MINSTREL_TRUNC(100000 * (prob_ewma / usecs));

  }

  /* find & sort topmost throughput rates */
  static inline void
  minstrel_sort_best_tp_rates(struct minstrel_sta_info *mi, int i, u8 *tp_list)
  {

  	int j;
  	struct minstrel_rate_stats *tmp_mrs;

  	struct minstrel_rate_stats *cur_mrs = &mi->r[i].stats;

  	for (j = MAX_THR_RATES; j > 0; --j) {

  		tmp_mrs = &mi->r[tp_list[j - 1]].stats;

  		if (minstrel_get_tp_avg(&mi->r[i], cur_mrs->prob_ewma) <=
  		    minstrel_get_tp_avg(&mi->r[tp_list[j - 1]], tmp_mrs->prob_ewma))
  			break;

  	}

  	if (j < MAX_THR_RATES - 1)
  		memmove(&tp_list[j + 1], &tp_list[j], MAX_THR_RATES - (j + 1));
  	if (j < MAX_THR_RATES)
  		tp_list[j] = i;
  }

  static void

  minstrel_set_rate(struct minstrel_sta_info *mi, struct ieee80211_sta_rates *ratetbl,
  		  int offset, int idx)
  {
  	struct minstrel_rate *r = &mi->r[idx];
  
  	ratetbl->rate[offset].idx = r->rix;
  	ratetbl->rate[offset].count = r->adjusted_retry_count;
  	ratetbl->rate[offset].count_cts = r->retry_count_cts;

  	ratetbl->rate[offset].count_rts = r->stats.retry_count_rtscts;

  }
  
  static void
  minstrel_update_rates(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
  {
  	struct ieee80211_sta_rates *ratetbl;
  	int i = 0;
  
  	ratetbl = kzalloc(sizeof(*ratetbl), GFP_ATOMIC);
  	if (!ratetbl)
  		return;
  
  	/* Start with max_tp_rate */
  	minstrel_set_rate(mi, ratetbl, i++, mi->max_tp_rate[0]);
  
  	if (mp->hw->max_rates >= 3) {
  		/* At least 3 tx rates supported, use max_tp_rate2 next */
  		minstrel_set_rate(mi, ratetbl, i++, mi->max_tp_rate[1]);
  	}
  
  	if (mp->hw->max_rates >= 2) {
  		/* At least 2 tx rates supported, use max_prob_rate next */
  		minstrel_set_rate(mi, ratetbl, i++, mi->max_prob_rate);
  	}
  
  	/* Use lowest rate last */
  	ratetbl->rate[i].idx = mi->lowest_rix;
  	ratetbl->rate[i].count = mp->max_retry;
  	ratetbl->rate[i].count_cts = mp->max_retry;
  	ratetbl->rate[i].count_rts = mp->max_retry;
  
  	rate_control_set_rates(mp->hw, mi->sta, ratetbl);
  }

  /*

  * Recalculate statistics and counters of a given rate

  */
  void
  minstrel_calc_rate_stats(struct minstrel_rate_stats *mrs)
  {

  	unsigned int cur_prob;

  	if (unlikely(mrs->attempts > 0)) {
  		mrs->sample_skipped = 0;

  		cur_prob = MINSTREL_FRAC(mrs->success, mrs->attempts);

  		if (unlikely(!mrs->att_hist)) {

  			mrs->prob_ewma = cur_prob;

  		} else {
  			/* update exponential weighted moving variance */

  			mrs->prob_ewmv = minstrel_ewmv(mrs->prob_ewmv,
  							cur_prob,
  							mrs->prob_ewma,
  							EWMA_LEVEL);

  
  			/*update exponential weighted moving avarage */

  			mrs->prob_ewma = minstrel_ewma(mrs->prob_ewma,

  						       cur_prob,

  						       EWMA_LEVEL);
  		}

  		mrs->att_hist += mrs->attempts;
  		mrs->succ_hist += mrs->success;
  	} else {
  		mrs->sample_skipped++;
  	}
  
  	mrs->last_success = mrs->success;
  	mrs->last_attempts = mrs->attempts;
  	mrs->success = 0;
  	mrs->attempts = 0;
  }

  static void

  minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
  {

  	u8 tmp_tp_rate[MAX_THR_RATES];
  	u8 tmp_prob_rate = 0;

  	int i, tmp_cur_tp, tmp_prob_tp;

  	for (i = 0; i < MAX_THR_RATES; i++)

  	    tmp_tp_rate[i] = 0;

  	for (i = 0; i < mi->n_rates; i++) {
  		struct minstrel_rate *mr = &mi->r[i];

  		struct minstrel_rate_stats *mrs = &mi->r[i].stats;

  		struct minstrel_rate_stats *tmp_mrs = &mi->r[tmp_prob_rate].stats;

  		/* Update statistics of success probability per rate */

  		minstrel_calc_rate_stats(mrs);

  
  		/* Sample less often below the 10% chance of success.
  		 * Sample less often above the 95% chance of success. */

  		if (mrs->prob_ewma > MINSTREL_FRAC(95, 100) ||
  		    mrs->prob_ewma < MINSTREL_FRAC(10, 100)) {

  			mr->adjusted_retry_count = mrs->retry_count >> 1;

  			if (mr->adjusted_retry_count > 2)
  				mr->adjusted_retry_count = 2;

  			mr->sample_limit = 4;

  		} else {

  			mr->sample_limit = -1;

  			mr->adjusted_retry_count = mrs->retry_count;

  		}
  		if (!mr->adjusted_retry_count)
  			mr->adjusted_retry_count = 2;

  		minstrel_sort_best_tp_rates(mi, i, tmp_tp_rate);
  
  		/* To determine the most robust rate (max_prob_rate) used at
  		 * 3rd mmr stage we distinct between two cases:
  		 * (1) if any success probabilitiy >= 95%, out of those rates
  		 * choose the maximum throughput rate as max_prob_rate
  		 * (2) if all success probabilities < 95%, the rate with

  		 * highest success probability is chosen as max_prob_rate */

  		if (mrs->prob_ewma >= MINSTREL_FRAC(95, 100)) {

  			tmp_cur_tp = minstrel_get_tp_avg(mr, mrs->prob_ewma);
  			tmp_prob_tp = minstrel_get_tp_avg(&mi->r[tmp_prob_rate],
  							  tmp_mrs->prob_ewma);

  			if (tmp_cur_tp >= tmp_prob_tp)

  				tmp_prob_rate = i;
  		} else {

  			if (mrs->prob_ewma >= tmp_mrs->prob_ewma)

  				tmp_prob_rate = i;

  		}
  	}

  	/* Assign the new rate set */
  	memcpy(mi->max_tp_rate, tmp_tp_rate, sizeof(mi->max_tp_rate));
  	mi->max_prob_rate = tmp_prob_rate;

  #ifdef CONFIG_MAC80211_DEBUGFS
  	/* use fixed index if set */
  	if (mp->fixed_rate_idx != -1) {
  		mi->max_tp_rate[0] = mp->fixed_rate_idx;
  		mi->max_tp_rate[1] = mp->fixed_rate_idx;
  		mi->max_prob_rate = mp->fixed_rate_idx;
  	}
  #endif

  	/* Reset update timer */

  	mi->last_stats_update = jiffies;

  
  	minstrel_update_rates(mp, mi);

  }
  
  static void
  minstrel_tx_status(void *priv, struct ieee80211_supported_band *sband,

  		   void *priv_sta, struct ieee80211_tx_status *st)

  {

  	struct ieee80211_tx_info *info = st->info;

  	struct minstrel_priv *mp = priv;

  	struct minstrel_sta_info *mi = priv_sta;

  	struct ieee80211_tx_rate *ar = info->status.rates;
  	int i, ndx;
  	int success;

  	success = !!(info->flags & IEEE80211_TX_STAT_ACK);

  	for (i = 0; i < IEEE80211_TX_MAX_RATES; i++) {
  		if (ar[i].idx < 0)

  			break;

  		ndx = rix_to_ndx(mi, ar[i].idx);

  		if (ndx < 0)
  			continue;

  		mi->r[ndx].stats.attempts += ar[i].count;

  		if ((i != IEEE80211_TX_MAX_RATES - 1) && (ar[i + 1].idx < 0))

  			mi->r[ndx].stats.success += success;

  	}
  
  	if ((info->flags & IEEE80211_TX_CTL_RATE_CTRL_PROBE) && (i >= 0))

  		mi->sample_packets++;

  
  	if (mi->sample_deferred > 0)
  		mi->sample_deferred--;

  	if (time_after(jiffies, mi->last_stats_update +

  				(mp->update_interval * HZ) / 1000))
  		minstrel_update_stats(mp, mi);

  }
  
  
  static inline unsigned int
  minstrel_get_retry_count(struct minstrel_rate *mr,

  			 struct ieee80211_tx_info *info)

  {

  	u8 retry = mr->adjusted_retry_count;

  	if (info->control.use_rts)

  		retry = max_t(u8, 2, min(mr->stats.retry_count_rtscts, retry));

  	else if (info->control.use_cts_prot)

  		retry = max_t(u8, 2, min(mr->retry_count_cts, retry));

  	return retry;
  }
  
  
  static int
  minstrel_get_next_sample(struct minstrel_sta_info *mi)
  {
  	unsigned int sample_ndx;

  	sample_ndx = SAMPLE_TBL(mi, mi->sample_row, mi->sample_column);
  	mi->sample_row++;

  	if ((int) mi->sample_row >= mi->n_rates) {

  		mi->sample_row = 0;

  		mi->sample_column++;
  		if (mi->sample_column >= SAMPLE_COLUMNS)
  			mi->sample_column = 0;
  	}
  	return sample_ndx;
  }

  static void

  minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
  		  void *priv_sta, struct ieee80211_tx_rate_control *txrc)

  {

  	struct sk_buff *skb = txrc->skb;

  	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
  	struct minstrel_sta_info *mi = priv_sta;
  	struct minstrel_priv *mp = priv;

  	struct ieee80211_tx_rate *rate = &info->control.rates[0];
  	struct minstrel_rate *msr, *mr;
  	unsigned int ndx;

  	bool mrr_capable;

  	bool prev_sample;

  	int delta;

  	int sampling_ratio;

  	/* management/no-ack frames do not use rate control */

  	if (rate_control_send_low(sta, priv_sta, txrc))

  		return;

  	/* check multi-rate-retry capabilities & adjust lookaround_rate */
  	mrr_capable = mp->has_mrr &&
  		      !txrc->rts &&
  		      !txrc->bss_conf->use_cts_prot;
  	if (mrr_capable)
  		sampling_ratio = mp->lookaround_rate_mrr;
  	else
  		sampling_ratio = mp->lookaround_rate;

  	/* increase sum packet counter */

  	mi->total_packets++;

  #ifdef CONFIG_MAC80211_DEBUGFS
  	if (mp->fixed_rate_idx != -1)
  		return;
  #endif

  	/* Don't use EAPOL frames for sampling on non-mrr hw */
  	if (mp->hw->max_rates == 1 &&
  	    (info->control.flags & IEEE80211_TX_CTRL_PORT_CTRL_PROTO))
  		return;

  	delta = (mi->total_packets * sampling_ratio / 100) -
  			(mi->sample_packets + mi->sample_deferred / 2);

  	/* delta < 0: no sampling required */

  	prev_sample = mi->prev_sample;

  	mi->prev_sample = false;
  	if (delta < 0 || (!mrr_capable && prev_sample))
  		return;

  	if (mi->total_packets >= 10000) {

  		mi->sample_deferred = 0;

  		mi->sample_packets = 0;
  		mi->total_packets = 0;

  	} else if (delta > mi->n_rates * 2) {
  		/* With multi-rate retry, not every planned sample
  		 * attempt actually gets used, due to the way the retry
  		 * chain is set up - [max_tp,sample,prob,lowest] for
  		 * sample_rate < max_tp.
  		 *
  		 * If there's too much sampling backlog and the link
  		 * starts getting worse, minstrel would start bursting
  		 * out lots of sampling frames, which would result
  		 * in a large throughput loss. */

  		mi->sample_packets += (delta - mi->n_rates * 2);

  	}
  
  	/* get next random rate sample */
  	ndx = minstrel_get_next_sample(mi);
  	msr = &mi->r[ndx];
  	mr = &mi->r[mi->max_tp_rate[0]];
  
  	/* Decide if direct ( 1st mrr stage) or indirect (2nd mrr stage)
  	 * rate sampling method should be used.
  	 * Respect such rates that are not sampled for 20 interations.
  	 */
  	if (mrr_capable &&
  	    msr->perfect_tx_time > mr->perfect_tx_time &&

  	    msr->stats.sample_skipped < 20) {

  		/* Only use IEEE80211_TX_CTL_RATE_CTRL_PROBE to mark
  		 * packets that have the sampling rate deferred to the
  		 * second MRR stage. Increase the sample counter only
  		 * if the deferred sample rate was actually used.
  		 * Use the sample_deferred counter to make sure that
  		 * the sampling is not done in large bursts */
  		info->flags |= IEEE80211_TX_CTL_RATE_CTRL_PROBE;
  		rate++;
  		mi->sample_deferred++;
  	} else {

  		if (!msr->sample_limit)

  			return;

  		mi->sample_packets++;

  		if (msr->sample_limit > 0)
  			msr->sample_limit--;

  	}

  
  	/* If we're not using MRR and the sampling rate already
  	 * has a probability of >95%, we shouldn't be attempting
  	 * to use it, as this only wastes precious airtime */

  	if (!mrr_capable &&

  	   (mi->r[ndx].stats.prob_ewma > MINSTREL_FRAC(95, 100)))

  		return;

  	mi->prev_sample = true;

  	rate->idx = mi->r[ndx].rix;
  	rate->count = minstrel_get_retry_count(&mi->r[ndx], info);

  }
  
  
  static void

  calc_rate_durations(enum nl80211_band band,

  		    struct minstrel_rate *d,

  		    struct ieee80211_rate *rate,
  		    struct cfg80211_chan_def *chandef)

  {
  	int erp = !!(rate->flags & IEEE80211_RATE_ERP_G);

  	int shift = ieee80211_chandef_get_shift(chandef);

  	d->perfect_tx_time = ieee80211_frame_duration(band, 1200,

  			DIV_ROUND_UP(rate->bitrate, 1 << shift), erp, 1,
  			shift);

  	d->ack_time = ieee80211_frame_duration(band, 10,

  			DIV_ROUND_UP(rate->bitrate, 1 << shift), erp, 1,
  			shift);

  }
  
  static void
  init_sample_table(struct minstrel_sta_info *mi)
  {
  	unsigned int i, col, new_idx;

  	u8 rnd[8];
  
  	mi->sample_column = 0;

  	mi->sample_row = 0;

  	memset(mi->sample_table, 0xff, SAMPLE_COLUMNS * mi->n_rates);

  
  	for (col = 0; col < SAMPLE_COLUMNS; col++) {

  		prandom_bytes(rnd, sizeof(rnd));

  		for (i = 0; i < mi->n_rates; i++) {

  			new_idx = (i + rnd[i & 7]) % mi->n_rates;

  			while (SAMPLE_TBL(mi, new_idx, col) != 0xff)
  				new_idx = (new_idx + 1) % mi->n_rates;

  			SAMPLE_TBL(mi, new_idx, col) = i;

  		}
  	}
  }
  
  static void
  minstrel_rate_init(void *priv, struct ieee80211_supported_band *sband,

  		   struct cfg80211_chan_def *chandef,
  		   struct ieee80211_sta *sta, void *priv_sta)

  {
  	struct minstrel_sta_info *mi = priv_sta;
  	struct minstrel_priv *mp = priv;

  	struct ieee80211_rate *ctl_rate;

  	unsigned int i, n = 0;
  	unsigned int t_slot = 9; /* FIXME: get real slot time */

  	u32 rate_flags;

  	mi->sta = sta;

  	mi->lowest_rix = rate_lowest_index(sband, sta);

  	ctl_rate = &sband->bitrates[mi->lowest_rix];

  	mi->sp_ack_dur = ieee80211_frame_duration(sband->band, 10,
  				ctl_rate->bitrate,

  				!!(ctl_rate->flags & IEEE80211_RATE_ERP_G), 1,
  				ieee80211_chandef_get_shift(chandef));

  	rate_flags = ieee80211_chandef_rate_flags(&mp->hw->conf.chandef);

  	memset(mi->max_tp_rate, 0, sizeof(mi->max_tp_rate));
  	mi->max_prob_rate = 0;

  	for (i = 0; i < sband->n_bitrates; i++) {
  		struct minstrel_rate *mr = &mi->r[n];

  		struct minstrel_rate_stats *mrs = &mi->r[n].stats;

  		unsigned int tx_time = 0, tx_time_cts = 0, tx_time_rtscts = 0;
  		unsigned int tx_time_single;
  		unsigned int cw = mp->cw_min;

  		int shift;

  
  		if (!rate_supported(sta, sband->band, i))
  			continue;

  		if ((rate_flags & sband->bitrates[i].flags) != rate_flags)
  			continue;

  		n++;
  		memset(mr, 0, sizeof(*mr));

  		memset(mrs, 0, sizeof(*mrs));

  
  		mr->rix = i;

  		shift = ieee80211_chandef_get_shift(chandef);
  		mr->bitrate = DIV_ROUND_UP(sband->bitrates[i].bitrate,
  					   (1 << shift) * 5);
  		calc_rate_durations(sband->band, mr, &sband->bitrates[i],
  				    chandef);

  
  		/* calculate maximum number of retransmissions before
  		 * fallback (based on maximum segment size) */

  		mr->sample_limit = -1;

  		mrs->retry_count = 1;

  		mr->retry_count_cts = 1;

  		mrs->retry_count_rtscts = 1;

  		tx_time = mr->perfect_tx_time + mi->sp_ack_dur;
  		do {
  			/* add one retransmission */
  			tx_time_single = mr->ack_time + mr->perfect_tx_time;
  
  			/* contention window */

  			tx_time_single += (t_slot * cw) >> 1;
  			cw = min((cw << 1) | 1, mp->cw_max);

  
  			tx_time += tx_time_single;
  			tx_time_cts += tx_time_single + mi->sp_ack_dur;
  			tx_time_rtscts += tx_time_single + 2 * mi->sp_ack_dur;
  			if ((tx_time_cts < mp->segment_size) &&
  				(mr->retry_count_cts < mp->max_retry))
  				mr->retry_count_cts++;
  			if ((tx_time_rtscts < mp->segment_size) &&

  				(mrs->retry_count_rtscts < mp->max_retry))
  				mrs->retry_count_rtscts++;

  		} while ((tx_time < mp->segment_size) &&

  				(++mr->stats.retry_count < mp->max_retry));
  		mr->adjusted_retry_count = mrs->retry_count;

  		if (!(sband->bitrates[i].flags & IEEE80211_RATE_ERP_G))

  			mr->retry_count_cts = mrs->retry_count;

  	}
  
  	for (i = n; i < sband->n_bitrates; i++) {
  		struct minstrel_rate *mr = &mi->r[i];
  		mr->rix = -1;
  	}
  
  	mi->n_rates = n;

  	mi->last_stats_update = jiffies;

  
  	init_sample_table(mi);

  	minstrel_update_rates(mp, mi);

  }
  
  static void *
  minstrel_alloc_sta(void *priv, struct ieee80211_sta *sta, gfp_t gfp)
  {
  	struct ieee80211_supported_band *sband;
  	struct minstrel_sta_info *mi;
  	struct minstrel_priv *mp = priv;
  	struct ieee80211_hw *hw = mp->hw;
  	int max_rates = 0;
  	int i;
  
  	mi = kzalloc(sizeof(struct minstrel_sta_info), gfp);
  	if (!mi)
  		return NULL;

  	for (i = 0; i < NUM_NL80211_BANDS; i++) {

  		sband = hw->wiphy->bands[i];

  		if (sband && sband->n_bitrates > max_rates)

  			max_rates = sband->n_bitrates;
  	}
  
  	mi->r = kzalloc(sizeof(struct minstrel_rate) * max_rates, gfp);
  	if (!mi->r)
  		goto error;
  
  	mi->sample_table = kmalloc(SAMPLE_COLUMNS * max_rates, gfp);
  	if (!mi->sample_table)
  		goto error1;

  	mi->last_stats_update = jiffies;

  	return mi;
  
  error1:
  	kfree(mi->r);
  error:
  	kfree(mi);
  	return NULL;
  }
  
  static void
  minstrel_free_sta(void *priv, struct ieee80211_sta *sta, void *priv_sta)
  {
  	struct minstrel_sta_info *mi = priv_sta;
  
  	kfree(mi->sample_table);
  	kfree(mi->r);
  	kfree(mi);
  }

  static void
  minstrel_init_cck_rates(struct minstrel_priv *mp)
  {
  	static const int bitrates[4] = { 10, 20, 55, 110 };
  	struct ieee80211_supported_band *sband;

  	u32 rate_flags = ieee80211_chandef_rate_flags(&mp->hw->conf.chandef);

  	int i, j;

  	sband = mp->hw->wiphy->bands[NL80211_BAND_2GHZ];

  	if (!sband)
  		return;
  
  	for (i = 0, j = 0; i < sband->n_bitrates; i++) {
  		struct ieee80211_rate *rate = &sband->bitrates[i];
  
  		if (rate->flags & IEEE80211_RATE_ERP_G)
  			continue;

  		if ((rate_flags & sband->bitrates[i].flags) != rate_flags)
  			continue;

  		for (j = 0; j < ARRAY_SIZE(bitrates); j++) {
  			if (rate->bitrate != bitrates[j])
  				continue;
  
  			mp->cck_rates[j] = i;
  			break;
  		}
  	}
  }

  static void *
  minstrel_alloc(struct ieee80211_hw *hw, struct dentry *debugfsdir)
  {
  	struct minstrel_priv *mp;
  
  	mp = kzalloc(sizeof(struct minstrel_priv), GFP_ATOMIC);
  	if (!mp)
  		return NULL;
  
  	/* contention window settings
  	 * Just an approximation. Using the per-queue values would complicate
  	 * the calculations and is probably unnecessary */
  	mp->cw_min = 15;
  	mp->cw_max = 1023;
  
  	/* number of packets (in %) to use for sampling other rates
  	 * sample less often for non-mrr packets, because the overhead
  	 * is much higher than with mrr */
  	mp->lookaround_rate = 5;
  	mp->lookaround_rate_mrr = 10;

  	/* maximum time that the hw is allowed to stay in one MRR segment */
  	mp->segment_size = 6000;

  	if (hw->max_rate_tries > 0)
  		mp->max_retry = hw->max_rate_tries;

  	else
  		/* safe default, does not necessarily have to match hw properties */
  		mp->max_retry = 7;

  	if (hw->max_rates >= 4)

  		mp->has_mrr = true;
  
  	mp->hw = hw;
  	mp->update_interval = 100;

  #ifdef CONFIG_MAC80211_DEBUGFS
  	mp->fixed_rate_idx = (u32) -1;
  	mp->dbg_fixed_rate = debugfs_create_u32("fixed_rate_idx",
  			S_IRUGO | S_IWUGO, debugfsdir, &mp->fixed_rate_idx);
  #endif

  	minstrel_init_cck_rates(mp);

  	return mp;
  }
  
  static void
  minstrel_free(void *priv)
  {

  #ifdef CONFIG_MAC80211_DEBUGFS
  	debugfs_remove(((struct minstrel_priv *)priv)->dbg_fixed_rate);
  #endif

  	kfree(priv);
  }

  static u32 minstrel_get_expected_throughput(void *priv_sta)
  {
  	struct minstrel_sta_info *mi = priv_sta;

  	struct minstrel_rate_stats *tmp_mrs;

  	int idx = mi->max_tp_rate[0];

  	int tmp_cur_tp;

  
  	/* convert pkt per sec in kbps (1200 is the average pkt size used for
  	 * computing cur_tp
  	 */

  	tmp_mrs = &mi->r[idx].stats;

  	tmp_cur_tp = minstrel_get_tp_avg(&mi->r[idx], tmp_mrs->prob_ewma) * 10;

  	tmp_cur_tp = tmp_cur_tp * 1200 * 8 / 1024;
  
  	return tmp_cur_tp;

  }

  const struct rate_control_ops mac80211_minstrel = {

  	.name = "minstrel",

  	.tx_status_ext = minstrel_tx_status,

  	.get_rate = minstrel_get_rate,
  	.rate_init = minstrel_rate_init,

  	.alloc = minstrel_alloc,
  	.free = minstrel_free,
  	.alloc_sta = minstrel_alloc_sta,
  	.free_sta = minstrel_free_sta,
  #ifdef CONFIG_MAC80211_DEBUGFS
  	.add_sta_debugfs = minstrel_add_sta_debugfs,
  	.remove_sta_debugfs = minstrel_remove_sta_debugfs,
  #endif

  	.get_expected_throughput = minstrel_get_expected_throughput,

  };
  
  int __init
  rc80211_minstrel_init(void)
  {
  	return ieee80211_rate_control_register(&mac80211_minstrel);
  }
  
  void
  rc80211_minstrel_exit(void)
  {
  	ieee80211_rate_control_unregister(&mac80211_minstrel);
  }