rc80211_minstrel_ht.c

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/*
 * Copyright (C) 2010 Felix Fietkau <[email protected]>
 *
 * 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);

    /*
     * Sampling might add some overhead (RTS, no aggregation)
     * to the frame. Hence, don't use sampling for the currently
     * used max TP rate.
     */
    if (sample_idx == mi->max_tp_rate)
        return -1;
    /*
     * 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) {
        mi->max_tp_rate = mp->fixed_rate_idx;
        mi->max_tp_rate2 = mp->fixed_rate_idx;
        mi->max_prob_rate = mp->fixed_rate_idx;
        sample_idx = -1;
    }
#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)
{
    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;
    u16 sta_cap = sta->ht_cap.cap;
    int n_supported = 0;
    int ack_dur;
    int stbc;
    int i;
    unsigned int smps;

    /* 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(sband->band, 10, 60, 1, 1);
    mi->overhead = ieee80211_frame_duration(sband->band, 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;

    smps = (sta_cap & IEEE80211_HT_CAP_SM_PS) >>
        IEEE80211_HT_CAP_SM_PS_SHIFT;

    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;

        /* Mark MCS > 7 as unsupported if STA is in static SMPS mode */
        if (smps == WLAN_HT_CAP_SM_PS_STATIC &&
            minstrel_mcs_groups[i].streams > 1)
            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)
{
    minstrel_ht_update_caps(priv, sband, sta, priv_sta);
}

static void
minstrel_ht_rate_update(void *priv, struct ieee80211_supported_band *sband,
                        struct ieee80211_sta *sta, void *priv_sta,
                        u32 changed)
{
    minstrel_ht_update_caps(priv, sband, sta, priv_sta);
}

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(*msp), 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);
}