swh:1:snp:173f8deb0c56c557784b4fd217e7608ac6197844
Tip revision: d5226fa6dbae0569ee43ecfc08bdcd6770fc4755 authored by Linus Torvalds on 27 January 2020, 00:23:03 UTC
Linux 5.5
Linux 5.5
Tip revision: d5226fa
airtime.c
// SPDX-License-Identifier: ISC
/*
* Copyright (C) 2019 Felix Fietkau <nbd@nbd.name>
*/
#include <net/mac80211.h>
#include "ieee80211_i.h"
#include "sta_info.h"
#define AVG_PKT_SIZE 1024
/* Number of bits for an average sized packet */
#define MCS_NBITS (AVG_PKT_SIZE << 3)
/* Number of kilo-symbols (symbols * 1024) for a packet with (bps) bits per
* symbol. We use k-symbols to avoid rounding in the _TIME macros below.
*/
#define MCS_N_KSYMS(bps) DIV_ROUND_UP(MCS_NBITS << 10, (bps))
/* Transmission time (in 1024 * usec) for a packet containing (ksyms) * 1024
* symbols.
*/
#define MCS_SYMBOL_TIME(sgi, ksyms) \
(sgi ? \
((ksyms) * 4 * 18) / 20 : /* 3.6 us per sym */ \
((ksyms) * 4) /* 4.0 us per sym */ \
)
/* Transmit duration for the raw data part of an average sized packet */
#define MCS_DURATION(streams, sgi, bps) \
((u32)MCS_SYMBOL_TIME(sgi, MCS_N_KSYMS((streams) * (bps))))
#define MCS_DURATION_S(shift, streams, sgi, bps) \
((u16)((MCS_DURATION(streams, sgi, bps) >> shift)))
/* These should match the values in enum nl80211_he_gi */
#define HE_GI_08 0
#define HE_GI_16 1
#define HE_GI_32 2
/* Transmission time (1024 usec) for a packet containing (ksyms) * k-symbols */
#define HE_SYMBOL_TIME(gi, ksyms) \
(gi == HE_GI_08 ? \
((ksyms) * 16 * 17) / 20 : /* 13.6 us per sym */ \
(gi == HE_GI_16 ? \
((ksyms) * 16 * 18) / 20 : /* 14.4 us per sym */ \
((ksyms) * 16) /* 16.0 us per sym */ \
))
/* Transmit duration for the raw data part of an average sized packet */
#define HE_DURATION(streams, gi, bps) \
((u32)HE_SYMBOL_TIME(gi, MCS_N_KSYMS((streams) * (bps))))
#define HE_DURATION_S(shift, streams, gi, bps) \
(HE_DURATION(streams, gi, bps) >> shift)
#define BW_20 0
#define BW_40 1
#define BW_80 2
#define BW_160 3
/*
* Define group sort order: HT40 -> SGI -> #streams
*/
#define IEEE80211_MAX_STREAMS 4
#define IEEE80211_HT_STREAM_GROUPS 4 /* BW(=2) * SGI(=2) */
#define IEEE80211_VHT_STREAM_GROUPS 8 /* BW(=4) * SGI(=2) */
#define IEEE80211_HE_MAX_STREAMS 8
#define IEEE80211_HE_STREAM_GROUPS 12 /* BW(=4) * GI(=3) */
#define IEEE80211_HT_GROUPS_NB (IEEE80211_MAX_STREAMS * \
IEEE80211_HT_STREAM_GROUPS)
#define IEEE80211_VHT_GROUPS_NB (IEEE80211_MAX_STREAMS * \
IEEE80211_VHT_STREAM_GROUPS)
#define IEEE80211_HE_GROUPS_NB (IEEE80211_HE_MAX_STREAMS * \
IEEE80211_HE_STREAM_GROUPS)
#define IEEE80211_GROUPS_NB (IEEE80211_HT_GROUPS_NB + \
IEEE80211_VHT_GROUPS_NB + \
IEEE80211_HE_GROUPS_NB)
#define IEEE80211_HT_GROUP_0 0
#define IEEE80211_VHT_GROUP_0 (IEEE80211_HT_GROUP_0 + IEEE80211_HT_GROUPS_NB)
#define IEEE80211_HE_GROUP_0 (IEEE80211_VHT_GROUP_0 + IEEE80211_VHT_GROUPS_NB)
#define MCS_GROUP_RATES 12
#define HT_GROUP_IDX(_streams, _sgi, _ht40) \
IEEE80211_HT_GROUP_0 + \
IEEE80211_MAX_STREAMS * 2 * _ht40 + \
IEEE80211_MAX_STREAMS * _sgi + \
_streams - 1
#define _MAX(a, b) (((a)>(b))?(a):(b))
#define GROUP_SHIFT(duration) \
_MAX(0, 16 - __builtin_clz(duration))
/* MCS rate information for an MCS group */
#define __MCS_GROUP(_streams, _sgi, _ht40, _s) \
[HT_GROUP_IDX(_streams, _sgi, _ht40)] = { \
.shift = _s, \
.duration = { \
MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 54 : 26), \
MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 108 : 52), \
MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 162 : 78), \
MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 216 : 104), \
MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 324 : 156), \
MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 432 : 208), \
MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 486 : 234), \
MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 540 : 260) \
} \
}
#define MCS_GROUP_SHIFT(_streams, _sgi, _ht40) \
GROUP_SHIFT(MCS_DURATION(_streams, _sgi, _ht40 ? 54 : 26))
#define MCS_GROUP(_streams, _sgi, _ht40) \
__MCS_GROUP(_streams, _sgi, _ht40, \
MCS_GROUP_SHIFT(_streams, _sgi, _ht40))
#define VHT_GROUP_IDX(_streams, _sgi, _bw) \
(IEEE80211_VHT_GROUP_0 + \
IEEE80211_MAX_STREAMS * 2 * (_bw) + \
IEEE80211_MAX_STREAMS * (_sgi) + \
(_streams) - 1)
#define BW2VBPS(_bw, r4, r3, r2, r1) \
(_bw == BW_160 ? r4 : _bw == BW_80 ? r3 : _bw == BW_40 ? r2 : r1)
#define __VHT_GROUP(_streams, _sgi, _bw, _s) \
[VHT_GROUP_IDX(_streams, _sgi, _bw)] = { \
.shift = _s, \
.duration = { \
MCS_DURATION_S(_s, _streams, _sgi, \
BW2VBPS(_bw, 234, 117, 54, 26)), \
MCS_DURATION_S(_s, _streams, _sgi, \
BW2VBPS(_bw, 468, 234, 108, 52)), \
MCS_DURATION_S(_s, _streams, _sgi, \
BW2VBPS(_bw, 702, 351, 162, 78)), \
MCS_DURATION_S(_s, _streams, _sgi, \
BW2VBPS(_bw, 936, 468, 216, 104)), \
MCS_DURATION_S(_s, _streams, _sgi, \
BW2VBPS(_bw, 1404, 702, 324, 156)), \
MCS_DURATION_S(_s, _streams, _sgi, \
BW2VBPS(_bw, 1872, 936, 432, 208)), \
MCS_DURATION_S(_s, _streams, _sgi, \
BW2VBPS(_bw, 2106, 1053, 486, 234)), \
MCS_DURATION_S(_s, _streams, _sgi, \
BW2VBPS(_bw, 2340, 1170, 540, 260)), \
MCS_DURATION_S(_s, _streams, _sgi, \
BW2VBPS(_bw, 2808, 1404, 648, 312)), \
MCS_DURATION_S(_s, _streams, _sgi, \
BW2VBPS(_bw, 3120, 1560, 720, 346)) \
} \
}
#define VHT_GROUP_SHIFT(_streams, _sgi, _bw) \
GROUP_SHIFT(MCS_DURATION(_streams, _sgi, \
BW2VBPS(_bw, 243, 117, 54, 26)))
#define VHT_GROUP(_streams, _sgi, _bw) \
__VHT_GROUP(_streams, _sgi, _bw, \
VHT_GROUP_SHIFT(_streams, _sgi, _bw))
#define HE_GROUP_IDX(_streams, _gi, _bw) \
(IEEE80211_HE_GROUP_0 + \
IEEE80211_HE_MAX_STREAMS * 3 * (_bw) + \
IEEE80211_HE_MAX_STREAMS * (_gi) + \
(_streams) - 1)
#define __HE_GROUP(_streams, _gi, _bw, _s) \
[HE_GROUP_IDX(_streams, _gi, _bw)] = { \
.shift = _s, \
.duration = { \
HE_DURATION_S(_s, _streams, _gi, \
BW2VBPS(_bw, 979, 489, 230, 115)), \
HE_DURATION_S(_s, _streams, _gi, \
BW2VBPS(_bw, 1958, 979, 475, 230)), \
HE_DURATION_S(_s, _streams, _gi, \
BW2VBPS(_bw, 2937, 1468, 705, 345)), \
HE_DURATION_S(_s, _streams, _gi, \
BW2VBPS(_bw, 3916, 1958, 936, 475)), \
HE_DURATION_S(_s, _streams, _gi, \
BW2VBPS(_bw, 5875, 2937, 1411, 705)), \
HE_DURATION_S(_s, _streams, _gi, \
BW2VBPS(_bw, 7833, 3916, 1872, 936)), \
HE_DURATION_S(_s, _streams, _gi, \
BW2VBPS(_bw, 8827, 4406, 2102, 1051)), \
HE_DURATION_S(_s, _streams, _gi, \
BW2VBPS(_bw, 9806, 4896, 2347, 1166)), \
HE_DURATION_S(_s, _streams, _gi, \
BW2VBPS(_bw, 11764, 5875, 2808, 1411)), \
HE_DURATION_S(_s, _streams, _gi, \
BW2VBPS(_bw, 13060, 6523, 3124, 1555)), \
HE_DURATION_S(_s, _streams, _gi, \
BW2VBPS(_bw, 14702, 7344, 3513, 1756)), \
HE_DURATION_S(_s, _streams, _gi, \
BW2VBPS(_bw, 16329, 8164, 3902, 1944)) \
} \
}
#define HE_GROUP_SHIFT(_streams, _gi, _bw) \
GROUP_SHIFT(HE_DURATION(_streams, _gi, \
BW2VBPS(_bw, 979, 489, 230, 115)))
#define HE_GROUP(_streams, _gi, _bw) \
__HE_GROUP(_streams, _gi, _bw, \
HE_GROUP_SHIFT(_streams, _gi, _bw))
struct mcs_group {
u8 shift;
u16 duration[MCS_GROUP_RATES];
};
static const struct mcs_group airtime_mcs_groups[] = {
MCS_GROUP(1, 0, BW_20),
MCS_GROUP(2, 0, BW_20),
MCS_GROUP(3, 0, BW_20),
MCS_GROUP(4, 0, BW_20),
MCS_GROUP(1, 1, BW_20),
MCS_GROUP(2, 1, BW_20),
MCS_GROUP(3, 1, BW_20),
MCS_GROUP(4, 1, BW_20),
MCS_GROUP(1, 0, BW_40),
MCS_GROUP(2, 0, BW_40),
MCS_GROUP(3, 0, BW_40),
MCS_GROUP(4, 0, BW_40),
MCS_GROUP(1, 1, BW_40),
MCS_GROUP(2, 1, BW_40),
MCS_GROUP(3, 1, BW_40),
MCS_GROUP(4, 1, BW_40),
VHT_GROUP(1, 0, BW_20),
VHT_GROUP(2, 0, BW_20),
VHT_GROUP(3, 0, BW_20),
VHT_GROUP(4, 0, BW_20),
VHT_GROUP(1, 1, BW_20),
VHT_GROUP(2, 1, BW_20),
VHT_GROUP(3, 1, BW_20),
VHT_GROUP(4, 1, BW_20),
VHT_GROUP(1, 0, BW_40),
VHT_GROUP(2, 0, BW_40),
VHT_GROUP(3, 0, BW_40),
VHT_GROUP(4, 0, BW_40),
VHT_GROUP(1, 1, BW_40),
VHT_GROUP(2, 1, BW_40),
VHT_GROUP(3, 1, BW_40),
VHT_GROUP(4, 1, BW_40),
VHT_GROUP(1, 0, BW_80),
VHT_GROUP(2, 0, BW_80),
VHT_GROUP(3, 0, BW_80),
VHT_GROUP(4, 0, BW_80),
VHT_GROUP(1, 1, BW_80),
VHT_GROUP(2, 1, BW_80),
VHT_GROUP(3, 1, BW_80),
VHT_GROUP(4, 1, BW_80),
VHT_GROUP(1, 0, BW_160),
VHT_GROUP(2, 0, BW_160),
VHT_GROUP(3, 0, BW_160),
VHT_GROUP(4, 0, BW_160),
VHT_GROUP(1, 1, BW_160),
VHT_GROUP(2, 1, BW_160),
VHT_GROUP(3, 1, BW_160),
VHT_GROUP(4, 1, BW_160),
HE_GROUP(1, HE_GI_08, BW_20),
HE_GROUP(2, HE_GI_08, BW_20),
HE_GROUP(3, HE_GI_08, BW_20),
HE_GROUP(4, HE_GI_08, BW_20),
HE_GROUP(5, HE_GI_08, BW_20),
HE_GROUP(6, HE_GI_08, BW_20),
HE_GROUP(7, HE_GI_08, BW_20),
HE_GROUP(8, HE_GI_08, BW_20),
HE_GROUP(1, HE_GI_16, BW_20),
HE_GROUP(2, HE_GI_16, BW_20),
HE_GROUP(3, HE_GI_16, BW_20),
HE_GROUP(4, HE_GI_16, BW_20),
HE_GROUP(5, HE_GI_16, BW_20),
HE_GROUP(6, HE_GI_16, BW_20),
HE_GROUP(7, HE_GI_16, BW_20),
HE_GROUP(8, HE_GI_16, BW_20),
HE_GROUP(1, HE_GI_32, BW_20),
HE_GROUP(2, HE_GI_32, BW_20),
HE_GROUP(3, HE_GI_32, BW_20),
HE_GROUP(4, HE_GI_32, BW_20),
HE_GROUP(5, HE_GI_32, BW_20),
HE_GROUP(6, HE_GI_32, BW_20),
HE_GROUP(7, HE_GI_32, BW_20),
HE_GROUP(8, HE_GI_32, BW_20),
HE_GROUP(1, HE_GI_08, BW_40),
HE_GROUP(2, HE_GI_08, BW_40),
HE_GROUP(3, HE_GI_08, BW_40),
HE_GROUP(4, HE_GI_08, BW_40),
HE_GROUP(5, HE_GI_08, BW_40),
HE_GROUP(6, HE_GI_08, BW_40),
HE_GROUP(7, HE_GI_08, BW_40),
HE_GROUP(8, HE_GI_08, BW_40),
HE_GROUP(1, HE_GI_16, BW_40),
HE_GROUP(2, HE_GI_16, BW_40),
HE_GROUP(3, HE_GI_16, BW_40),
HE_GROUP(4, HE_GI_16, BW_40),
HE_GROUP(5, HE_GI_16, BW_40),
HE_GROUP(6, HE_GI_16, BW_40),
HE_GROUP(7, HE_GI_16, BW_40),
HE_GROUP(8, HE_GI_16, BW_40),
HE_GROUP(1, HE_GI_32, BW_40),
HE_GROUP(2, HE_GI_32, BW_40),
HE_GROUP(3, HE_GI_32, BW_40),
HE_GROUP(4, HE_GI_32, BW_40),
HE_GROUP(5, HE_GI_32, BW_40),
HE_GROUP(6, HE_GI_32, BW_40),
HE_GROUP(7, HE_GI_32, BW_40),
HE_GROUP(8, HE_GI_32, BW_40),
HE_GROUP(1, HE_GI_08, BW_80),
HE_GROUP(2, HE_GI_08, BW_80),
HE_GROUP(3, HE_GI_08, BW_80),
HE_GROUP(4, HE_GI_08, BW_80),
HE_GROUP(5, HE_GI_08, BW_80),
HE_GROUP(6, HE_GI_08, BW_80),
HE_GROUP(7, HE_GI_08, BW_80),
HE_GROUP(8, HE_GI_08, BW_80),
HE_GROUP(1, HE_GI_16, BW_80),
HE_GROUP(2, HE_GI_16, BW_80),
HE_GROUP(3, HE_GI_16, BW_80),
HE_GROUP(4, HE_GI_16, BW_80),
HE_GROUP(5, HE_GI_16, BW_80),
HE_GROUP(6, HE_GI_16, BW_80),
HE_GROUP(7, HE_GI_16, BW_80),
HE_GROUP(8, HE_GI_16, BW_80),
HE_GROUP(1, HE_GI_32, BW_80),
HE_GROUP(2, HE_GI_32, BW_80),
HE_GROUP(3, HE_GI_32, BW_80),
HE_GROUP(4, HE_GI_32, BW_80),
HE_GROUP(5, HE_GI_32, BW_80),
HE_GROUP(6, HE_GI_32, BW_80),
HE_GROUP(7, HE_GI_32, BW_80),
HE_GROUP(8, HE_GI_32, BW_80),
HE_GROUP(1, HE_GI_08, BW_160),
HE_GROUP(2, HE_GI_08, BW_160),
HE_GROUP(3, HE_GI_08, BW_160),
HE_GROUP(4, HE_GI_08, BW_160),
HE_GROUP(5, HE_GI_08, BW_160),
HE_GROUP(6, HE_GI_08, BW_160),
HE_GROUP(7, HE_GI_08, BW_160),
HE_GROUP(8, HE_GI_08, BW_160),
HE_GROUP(1, HE_GI_16, BW_160),
HE_GROUP(2, HE_GI_16, BW_160),
HE_GROUP(3, HE_GI_16, BW_160),
HE_GROUP(4, HE_GI_16, BW_160),
HE_GROUP(5, HE_GI_16, BW_160),
HE_GROUP(6, HE_GI_16, BW_160),
HE_GROUP(7, HE_GI_16, BW_160),
HE_GROUP(8, HE_GI_16, BW_160),
HE_GROUP(1, HE_GI_32, BW_160),
HE_GROUP(2, HE_GI_32, BW_160),
HE_GROUP(3, HE_GI_32, BW_160),
HE_GROUP(4, HE_GI_32, BW_160),
HE_GROUP(5, HE_GI_32, BW_160),
HE_GROUP(6, HE_GI_32, BW_160),
HE_GROUP(7, HE_GI_32, BW_160),
HE_GROUP(8, HE_GI_32, BW_160),
};
static u32
ieee80211_calc_legacy_rate_duration(u16 bitrate, bool short_pre,
bool cck, int len)
{
u32 duration;
if (cck) {
duration = 144 + 48; /* preamble + PLCP */
if (short_pre)
duration >>= 1;
duration += 10; /* SIFS */
} else {
duration = 20 + 16; /* premable + SIFS */
}
len <<= 3;
duration += (len * 10) / bitrate;
return duration;
}
u32 ieee80211_calc_rx_airtime(struct ieee80211_hw *hw,
struct ieee80211_rx_status *status,
int len)
{
struct ieee80211_supported_band *sband;
const struct ieee80211_rate *rate;
bool sgi = status->enc_flags & RX_ENC_FLAG_SHORT_GI;
bool sp = status->enc_flags & RX_ENC_FLAG_SHORTPRE;
int bw, streams;
int group, idx;
u32 duration;
bool cck;
switch (status->bw) {
case RATE_INFO_BW_20:
bw = BW_20;
break;
case RATE_INFO_BW_40:
bw = BW_40;
break;
case RATE_INFO_BW_80:
bw = BW_80;
break;
case RATE_INFO_BW_160:
bw = BW_160;
break;
default:
WARN_ON_ONCE(1);
return 0;
}
switch (status->encoding) {
case RX_ENC_LEGACY:
if (WARN_ON_ONCE(status->band > NL80211_BAND_5GHZ))
return 0;
sband = hw->wiphy->bands[status->band];
if (!sband || status->rate_idx >= sband->n_bitrates)
return 0;
rate = &sband->bitrates[status->rate_idx];
cck = rate->flags & IEEE80211_RATE_MANDATORY_B;
return ieee80211_calc_legacy_rate_duration(rate->bitrate, sp,
cck, len);
case RX_ENC_VHT:
streams = status->nss;
idx = status->rate_idx;
group = VHT_GROUP_IDX(streams, sgi, bw);
break;
case RX_ENC_HT:
streams = ((status->rate_idx >> 3) & 3) + 1;
idx = status->rate_idx & 7;
group = HT_GROUP_IDX(streams, sgi, bw);
break;
case RX_ENC_HE:
streams = status->nss;
idx = status->rate_idx;
group = HE_GROUP_IDX(streams, status->he_gi, bw);
break;
default:
WARN_ON_ONCE(1);
return 0;
}
if (WARN_ON_ONCE((status->encoding != RX_ENC_HE && streams > 4) ||
(status->encoding == RX_ENC_HE && streams > 8)))
return 0;
duration = airtime_mcs_groups[group].duration[idx];
duration <<= airtime_mcs_groups[group].shift;
duration *= len;
duration /= AVG_PKT_SIZE;
duration /= 1024;
duration += 36 + (streams << 2);
return duration;
}
EXPORT_SYMBOL_GPL(ieee80211_calc_rx_airtime);
static u32 ieee80211_calc_tx_airtime_rate(struct ieee80211_hw *hw,
struct ieee80211_tx_rate *rate,
u8 band, int len)
{
struct ieee80211_rx_status stat = {
.band = band,
};
if (rate->idx < 0 || !rate->count)
return 0;
if (rate->flags & IEEE80211_TX_RC_80_MHZ_WIDTH)
stat.bw = RATE_INFO_BW_80;
else if (rate->flags & IEEE80211_TX_RC_40_MHZ_WIDTH)
stat.bw = RATE_INFO_BW_40;
else
stat.bw = RATE_INFO_BW_20;
stat.enc_flags = 0;
if (rate->flags & IEEE80211_TX_RC_USE_SHORT_PREAMBLE)
stat.enc_flags |= RX_ENC_FLAG_SHORTPRE;
if (rate->flags & IEEE80211_TX_RC_SHORT_GI)
stat.enc_flags |= RX_ENC_FLAG_SHORT_GI;
stat.rate_idx = rate->idx;
if (rate->flags & IEEE80211_TX_RC_VHT_MCS) {
stat.encoding = RX_ENC_VHT;
stat.rate_idx = ieee80211_rate_get_vht_mcs(rate);
stat.nss = ieee80211_rate_get_vht_nss(rate);
} else if (rate->flags & IEEE80211_TX_RC_MCS) {
stat.encoding = RX_ENC_HT;
} else {
stat.encoding = RX_ENC_LEGACY;
}
return ieee80211_calc_rx_airtime(hw, &stat, len);
}
u32 ieee80211_calc_tx_airtime(struct ieee80211_hw *hw,
struct ieee80211_tx_info *info,
int len)
{
u32 duration = 0;
int i;
for (i = 0; i < ARRAY_SIZE(info->status.rates); i++) {
struct ieee80211_tx_rate *rate = &info->status.rates[i];
u32 cur_duration;
cur_duration = ieee80211_calc_tx_airtime_rate(hw, rate,
info->band, len);
if (!cur_duration)
break;
duration += cur_duration * rate->count;
}
return duration;
}
EXPORT_SYMBOL_GPL(ieee80211_calc_tx_airtime);
u32 ieee80211_calc_expected_tx_airtime(struct ieee80211_hw *hw,
struct ieee80211_vif *vif,
struct ieee80211_sta *pubsta,
int len)
{
struct ieee80211_supported_band *sband;
struct ieee80211_chanctx_conf *conf;
int rateidx, shift = 0;
bool cck, short_pream;
u32 basic_rates;
u8 band = 0;
u16 rate;
len += 38; /* Ethernet header length */
conf = rcu_dereference(vif->chanctx_conf);
if (conf) {
band = conf->def.chan->band;
shift = ieee80211_chandef_get_shift(&conf->def);
}
if (pubsta) {
struct sta_info *sta = container_of(pubsta, struct sta_info,
sta);
return ieee80211_calc_tx_airtime_rate(hw,
&sta->tx_stats.last_rate,
band, len);
}
if (!conf)
return 0;
/* No station to get latest rate from, so calculate the worst-case
* duration using the lowest configured basic rate.
*/
sband = hw->wiphy->bands[band];
basic_rates = vif->bss_conf.basic_rates;
short_pream = vif->bss_conf.use_short_preamble;
rateidx = basic_rates ? ffs(basic_rates) - 1 : 0;
rate = sband->bitrates[rateidx].bitrate << shift;
cck = sband->bitrates[rateidx].flags & IEEE80211_RATE_MANDATORY_B;
return ieee80211_calc_legacy_rate_duration(rate, short_pream, cck, len);
}