mac80211: add the minstrel_ht rate control algorithm

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 824 insertions, 0 deletions

diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
new file mode 100644
index 000000000000..c23f08251da4
--- /dev/null
+++ b/net/mac80211/rc80211_minstrel_ht.c
@@ -0,0 +1,824 @@
+/*
+ * Copyright (C) 2010 Felix Fietkau <nbd@openwrt.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/netdevice.h>
+#include <linux/types.h>
+#include <linux/skbuff.h>
+#include <linux/debugfs.h>
+#include <linux/random.h>
+#include <linux/ieee80211.h>
+#include <net/mac80211.h>
+#include "rate.h"
+#include "rc80211_minstrel.h"
+#include "rc80211_minstrel_ht.h"
+
+#define AVG_PKT_SIZE    1200
+#define SAMPLE_COLUMNS  10
+#define EWMA_LEVEL              75
+
+/* Number of bits for an average sized packet */
+#define MCS_NBITS (AVG_PKT_SIZE << 3)
+
+/* Number of symbols for a packet with (bps) bits per symbol */
+#define MCS_NSYMS(bps) ((MCS_NBITS + (bps) - 1) / (bps))
+
+/* Transmission time for a packet containing (syms) symbols */
+#define MCS_SYMBOL_TIME(sgi, syms)                                      \
+        (sgi ?                                                          \
+          ((syms) * 18 + 4) / 5 :       /* syms * 3.6 us */             \
+          (syms) << 2                   /* syms * 4 us */               \
+        )
+
+/* Transmit duration for the raw data part of an average sized packet */
+#define MCS_DURATION(streams, sgi, bps) MCS_SYMBOL_TIME(sgi, MCS_NSYMS((streams) * (bps)))
+
+/* MCS rate information for an MCS group */
+#define MCS_GROUP(_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.
+ */
+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)
+{
+        int streams = (rate->idx / MCS_GROUP_RATES) + 1;
+        u32 flags = IEEE80211_TX_RC_SHORT_GI | IEEE80211_TX_RC_40_MHZ_WIDTH;
+        int i;
+
+        for (i = 0; i < ARRAY_SIZE(minstrel_mcs_groups); i++) {
+                if (minstrel_mcs_groups[i].streams != streams)
+                        continue;
+                if (minstrel_mcs_groups[i].flags != (rate->flags & flags))
+                        continue;
+
+                return i;
+        }
+
+        WARN_ON(1);
+        return 0;
+}
+
+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_priv *mp, 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_priv *mp, 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(mp, mr);
+                        minstrel_ht_calc_tp(mp, 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;
+                        }
+
+                        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 availble 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;
+                }
+
+                mr = minstrel_get_ratestats(mi, mg->max_tp_rate);
+                if (cur_tp < mr->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->count)
+                return false;
+
+        if (rate->idx < 0)
+                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, 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 minstrel_priv *mp, 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_state_tx[tid] != HT_AGG_STATE_IDLE))
+                return;
+
+        ieee80211_start_tx_ba_session(pubsta, tid);
+}
+
+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->status.ampdu_len) {
+                info->status.ampdu_ack_len = 1;
+                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 = 4 + 2 * MINSTREL_TRUNC(mi->avg_ampdu_len);
+                mi->sample_tries = 3;
+                mi->sample_count--;
+        }
+
+        if (info->flags & IEEE80211_TX_CTL_RATE_CTRL_PROBE) {
+                mi->sample_packets += info->status.ampdu_len;
+                minstrel_next_sample_idx(mi);
+        }
+
+        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 && (info->flags & IEEE80211_TX_STAT_ACK))
+                        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 (rate->attempts > 30 &&
+            MINSTREL_FRAC(rate->success, rate->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);
+                minstrel_aggr_check(mp, 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 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;
+        tx_time = 2 * (t_slot + mi->overhead + tx_time_data);
+        tx_time_rtscts = 2 * (t_slot + mi->overhead_rtscts + tx_time_data);
+        do {
+                cw = (cw << 1) | 1;
+                cw = min(cw, mp->cw_max);
+                tx_time += cw + t_slot + mi->overhead;
+                tx_time_rtscts += cw + t_slot + mi->overhead_rtscts;
+                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,
+                     struct ieee80211_tx_rate_control *txrc,
+                     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 (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 (txrc->short_preamble)
+                rate->flags |= IEEE80211_TX_RC_USE_SHORT_PREAMBLE;
+        if (txrc->rts || 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;
+
+        /*
+         * 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)))
+                goto next;
+
+        /*
+         * 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 < 10)
+                        goto next;
+
+                if (mi->sample_slow++ > 2)
+                        goto next;
+        }
+
+        return sample_idx;
+
+next:
+        minstrel_next_sample_idx(mi);
+        return -1;
+}
+
+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;
+
+        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;
+        sample_idx = minstrel_get_sample_rate(mp, mi);
+        if (sample_idx >= 0) {
+                minstrel_ht_set_rate(mp, mi, &ar[0], sample_idx,
+                        txrc, true, false);
+                minstrel_ht_set_rate(mp, mi, &ar[1], mi->max_tp_rate,
+                        txrc, false, true);
+                info->flags |= IEEE80211_TX_CTL_RATE_CTRL_PROBE;
+        } else {
+                minstrel_ht_set_rate(mp, mi, &ar[0], mi->max_tp_rate,
+                        txrc, false, false);
+                minstrel_ht_set_rate(mp, mi, &ar[1], mi->max_tp_rate2,
+                        txrc, false, true);
+        }
+        minstrel_ht_set_rate(mp, mi, &ar[2], mi->max_prob_rate, txrc, false, true);
+
+        ar[3].count = 0;
+        ar[3].idx = -1;
+
+        mi->total_packets++;
+
+        /* wraparound */
+        if (mi->total_packets == ~0) {
+                mi->total_packets = 0;
+                mi->sample_packets = 0;
+        }
+}
+
+static void
+minstrel_ht_update_caps(void *priv, struct ieee80211_supported_band *sband,
+                        struct ieee80211_sta *sta, void *priv_sta,
+                        enum nl80211_channel_type oper_chan_type)
+{
+        struct minstrel_priv *mp = priv;
+        struct minstrel_ht_sta_priv *msp = priv_sta;
+        struct minstrel_ht_sta *mi = &msp->ht;
+        struct ieee80211_mcs_info *mcs = &sta->ht_cap.mcs;
+        struct ieee80211_local *local = hw_to_local(mp->hw);
+        u16 sta_cap = sta->ht_cap.cap;
+        int ack_dur;
+        int stbc;
+        int i;
+
+        /* fall back to the old minstrel for legacy stations */
+        if (sta && !sta->ht_cap.ht_supported) {
+                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);
+        }
+
+        BUILD_BUG_ON(ARRAY_SIZE(minstrel_mcs_groups) !=
+                MINSTREL_MAX_STREAMS * MINSTREL_STREAM_GROUPS);
+
+        msp->is_ht = true;
+        memset(mi, 0, sizeof(*mi));
+        mi->stats_update = jiffies;
+
+        ack_dur = ieee80211_frame_duration(local, 10, 60, 1, 1);
+        mi->overhead = ieee80211_frame_duration(local, 0, 60, 1, 1) + ack_dur;
+        mi->overhead_rtscts = mi->overhead + 2 * ack_dur;
+
+        mi->avg_ampdu_len = MINSTREL_FRAC(1, 1);
+
+        /* When using MRR, sample more on the first attempt, without delay */
+        if (mp->has_mrr) {
+                mi->sample_count = 16;
+                mi->sample_wait = 0;
+        } else {
+                mi->sample_count = 8;
+                mi->sample_wait = 8;
+        }
+        mi->sample_tries = 4;
+
+        stbc = (sta_cap & IEEE80211_HT_CAP_RX_STBC) >>
+                IEEE80211_HT_CAP_RX_STBC_SHIFT;
+        mi->tx_flags |= stbc << IEEE80211_TX_CTL_STBC_SHIFT;
+
+        if (sta_cap & IEEE80211_HT_CAP_LDPC_CODING)
+                mi->tx_flags |= IEEE80211_TX_CTL_LDPC;
+
+        if (oper_chan_type != NL80211_CHAN_HT40MINUS &&
+            oper_chan_type != NL80211_CHAN_HT40PLUS)
+                sta_cap &= ~IEEE80211_HT_CAP_SUP_WIDTH_20_40;
+
+        for (i = 0; i < ARRAY_SIZE(mi->groups); i++) {
+                u16 req = 0;
+
+                mi->groups[i].supported = 0;
+                if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_SHORT_GI) {
+                        if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_40_MHZ_WIDTH)
+                                req |= IEEE80211_HT_CAP_SGI_40;
+                        else
+                                req |= IEEE80211_HT_CAP_SGI_20;
+                }
+
+                if (minstrel_mcs_groups[i].flags & IEEE80211_TX_RC_40_MHZ_WIDTH)
+                        req |= IEEE80211_HT_CAP_SUP_WIDTH_20_40;
+
+                if ((sta_cap & req) != req)
+                        continue;
+
+                mi->groups[i].supported =
+                        mcs->rx_mask[minstrel_mcs_groups[i].streams - 1];
+        }
+}
+
+static void
+minstrel_ht_rate_init(void *priv, struct ieee80211_supported_band *sband,
+                      struct ieee80211_sta *sta, void *priv_sta)
+{
+        struct minstrel_priv *mp = priv;
+
+        minstrel_ht_update_caps(priv, sband, sta, priv_sta, mp->hw->conf.channel_type);
+}
+
+static void
+minstrel_ht_rate_update(void *priv, struct ieee80211_supported_band *sband,
+                        struct ieee80211_sta *sta, void *priv_sta,
+                        u32 changed, enum nl80211_channel_type oper_chan_type)
+{
+        minstrel_ht_update_caps(priv, sband, sta, priv_sta, oper_chan_type);
+}
+
+static void *
+minstrel_ht_alloc_sta(void *priv, struct ieee80211_sta *sta, gfp_t gfp)
+{
+        struct ieee80211_supported_band *sband;
+        struct minstrel_ht_sta_priv *msp;
+        struct minstrel_priv *mp = priv;
+        struct ieee80211_hw *hw = mp->hw;
+        int max_rates = 0;
+        int i;
+
+        for (i = 0; i < IEEE80211_NUM_BANDS; i++) {
+                sband = hw->wiphy->bands[i];
+                if (sband && sband->n_bitrates > max_rates)
+                        max_rates = sband->n_bitrates;
+        }
+
+        msp = kzalloc(sizeof(struct minstrel_ht_sta), gfp);
+        if (!msp)
+                return NULL;
+
+        msp->ratelist = kzalloc(sizeof(struct minstrel_rate) * max_rates, gfp);
+        if (!msp->ratelist)
+                goto error;
+
+        msp->sample_table = kmalloc(SAMPLE_COLUMNS * max_rates, gfp);
+        if (!msp->sample_table)
+                goto error1;
+
+        return msp;
+
+error1:
+        kfree(msp->sample_table);
+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);
+}