net/mac80211/rc80211_minstrel.c - kernel/msm-4.19 - Gitiles

 /*
  * 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,
 		   struct ieee80211_sta *sta, void *priv_sta,
 		   struct ieee80211_tx_info *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_noskb = 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);
 }
	/*
	* 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,
	struct ieee80211_sta sta, void priv_sta,
	struct ieee80211_tx_info *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_noskb = 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);
	}