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Implement dynamic MCS selection based on signal strength in vWIFI driver #80

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0258f2a
Support Linux 6.15
horseface1110 May 30, 2025
151e1eb
Implement dynamic MCS selection based on signal strength in vWIFI driver
dingsen-Greenhorn Jun 7, 2025
af67f1d
Add manual MCS configuration via set_bitrate_mask
dingsen-Greenhorn Jun 8, 2025
c96febb
Expand MCS support manual 24–31 range for 4-stream
dingsen-Greenhorn Jun 12, 2025
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188 changes: 181 additions & 7 deletions vwifi.c
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Original file line number Diff line number Diff line change
Expand Up @@ -88,6 +88,8 @@ struct vwifi_vif {
struct wireless_dev wdev;
struct net_device *ndev;
struct net_device_stats stats;
int manual_mcs;
bool manual_mcs_set;

size_t ssid_len;
/* Currently connected BSS id */
Expand Down Expand Up @@ -1403,8 +1405,18 @@ static int vwifi_get_station(struct wiphy *wiphy,
sinfo->tx_failed = vif->stats.tx_dropped;
sinfo->tx_bytes = vif->stats.tx_bytes;
sinfo->rx_bytes = vif->stats.rx_bytes;


/* Log byte counters for debugging */
pr_info(
"vwifi: Station %pM tx_bytes %llu, rx_bytes %llu, tx_packets %u, "
"rx_packets %u, tx_failed %u\n",
mac, sinfo->tx_bytes, sinfo->rx_bytes, sinfo->tx_packets,
sinfo->rx_packets, sinfo->tx_failed);

/* For CFG80211_SIGNAL_TYPE_MBM, value is expressed in dBm */
sinfo->signal = rand_int_smooth(-100, -30, jiffies);
pr_info("vwifi: Station %pM signal %d dBm (raw)\n", mac, sinfo->signal);
sinfo->inactive_time = jiffies_to_msecs(jiffies - vif->active_time);
/*
* Using 802.11n (HT) as the PHY, configure as follows:
Expand All @@ -1425,15 +1437,92 @@ static int vwifi_get_station(struct wiphy *wiphy,
* https://semfionetworks.com/blog/mcs-table-updated-with-80211ax-data-rates/
* IEEE 802.11n : https://zh.wikipedia.org/zh-tw/IEEE_802.11n
*/
sinfo->rxrate.flags |= RATE_INFO_FLAGS_MCS;
sinfo->rxrate.mcs = 31;
/* Check vif->manual_mcs_set to use vif->manual_mcs if set;
* Assign modulation string for manual MCS ; else auto change based
* on signal strength
*/
int mcs_index;
const char *modulation;
const char *coding_rate;
if (vif->manual_mcs_set) {
mcs_index = vif->manual_mcs;
switch (mcs_index) {
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According to IEEE 802.11n, MCS indices 7, 15, 23, and 31 all use 64-QAM modulation.
You should revise the descriptions associated with each MCS index accordingly, or consider modifying your design if your intention was to differentiate based on modulation type.

ref:
mcsindex

case 24:
modulation = "BPSK";
coding_rate = "1/2";
break;
case 25:
modulation = "QPSK";
coding_rate = "1/2";
break;
case 26:
modulation = "QPSK";
coding_rate = "3/4";
break;
case 27:
modulation = "16-QAM";
coding_rate = "1/2";
break;
case 28:
modulation = "16-QAM";
coding_rate = "3/4";
break;
case 29:
modulation = "64-QAM";
coding_rate = "2/3";
break;
case 30:
modulation = "64-QAM";
coding_rate = "3/4";
break;
case 31:
modulation = "64-QAM";
coding_rate = "5/6";
break;
default:
pr_err("vwifi: Unsupported MCS index %d\n", mcs_index);
mcs_index = 24; /* Default to lowest 4-stream MCS */
modulation = "BPSK";
coding_rate = "1/2";
break;
}
pr_info("vwifi: Station %pM using manual MCS %d (%s, %s)\n", mac,
mcs_index, modulation, coding_rate);
} else {
if (sinfo->signal > -50) {
mcs_index = 31;
modulation = "64-QAM";
coding_rate = "5/6";
} else if (sinfo->signal > -70 && sinfo->signal <= -50) {
mcs_index = 28;
modulation = "16-QAM";
coding_rate = "3/4";
} else if (sinfo->signal > -90 && sinfo->signal <= -70) {
mcs_index = 25;
modulation = "QPSK";
coding_rate = "1/2";
} else {
mcs_index = 24;
modulation = "BPSK";
coding_rate = "1/2";
}
pr_info("vwifi: Station %pM signal %d dBm, using MCS %d (%s, %s)\n",
mac, sinfo->signal, mcs_index, modulation, coding_rate);
}
/* Configure RX and TX rates */
sinfo->rxrate.flags = RATE_INFO_FLAGS_MCS;
sinfo->rxrate.mcs = mcs_index;
sinfo->rxrate.bw = RATE_INFO_BW_20;
sinfo->rxrate.n_bonded_ch = 1;

sinfo->txrate.flags |= RATE_INFO_FLAGS_MCS;
sinfo->txrate.mcs = 31;
sinfo->txrate.flags = RATE_INFO_FLAGS_MCS;
sinfo->txrate.mcs = mcs_index;
sinfo->txrate.bw = RATE_INFO_BW_20;
sinfo->txrate.n_bonded_ch = 1;

/* Log rate configuration for verification */
pr_info("vwifi: Station %pM txrate MCS %d, rxrate MCS %d\n", mac,
sinfo->txrate.mcs, sinfo->rxrate.mcs);
return 0;
}

Expand Down Expand Up @@ -1677,8 +1766,13 @@ static int vwifi_start_ap(struct wiphy *wiphy,

/* Initialize hrtimer of beacon */
pr_info("vwifi: init beacon_timer.\n");
#if LINUX_VERSION_CODE >= KERNEL_VERSION(6, 15, 0)
hrtimer_setup(&vif->beacon_timer, vwifi_beacon, CLOCK_MONOTONIC,
HRTIMER_MODE_ABS_SOFT);
#else
hrtimer_init(&vif->beacon_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_SOFT);
vif->beacon_timer.function = vwifi_beacon;
#endif

if (!hrtimer_is_queued(&vif->beacon_timer)) {
u64 tsf, until_tbtt;
Expand Down Expand Up @@ -2145,6 +2239,66 @@ static int vwifi_leave_ibss(struct wiphy *wiphy, struct net_device *ndev)

return 0;
}
/* Callback to handle manual bitrate configuration via iw */
static int vwifi_set_bitrate_mask(struct wiphy *wiphy,
struct net_device *dev,
unsigned int link_id,
const u8 *peer,
const struct cfg80211_bitrate_mask *mask)
{
struct vwifi_vif *vif = netdev_priv(dev);
int mcs_index = -1;

if (!vif) {
pr_err("vwifi: Failed to get vwifi_vif for dev %s\n", dev->name);
return -EINVAL;
}

if (vif->sme_state != SME_CONNECTED) {
pr_err("vwifi: Dev %s not connected, cannot set bitrate\n", dev->name);
return -EINVAL;
}

pr_info("vwifi: set_bitrate_mask called for dev %s, link_id %u, peer %pM\n",
dev->name, link_id, peer ? peer : vif->bssid);
pr_info("vwifi: 2.4GHz MCS mask: %02x %02x %02x %02x\n",
mask->control[NL80211_BAND_2GHZ].ht_mcs[0],
mask->control[NL80211_BAND_2GHZ].ht_mcs[1],
mask->control[NL80211_BAND_2GHZ].ht_mcs[2],
mask->control[NL80211_BAND_2GHZ].ht_mcs[3]);

/* Find the requested MCS index */
for (int i = 0; i < 4; i++) {
if (mask->control[NL80211_BAND_2GHZ].ht_mcs[i]) {
for (int j = 0; j < 8; j++) {
if (mask->control[NL80211_BAND_2GHZ].ht_mcs[i] & (1 << j)) {
mcs_index = i * 8 + j;
pr_info("vwifi: Requested MCS index %d\n", mcs_index);
break;
}
}
if (mcs_index != -1)
break;
}
}

if (mcs_index == -1) {
pr_err("vwifi: No valid MCS index found\n");
return -EINVAL;
}

/* Restrict to supported 4-stream MCS indices 24–31 */
if (mcs_index < 24 || mcs_index > 31) {
pr_err("vwifi: Unsupported MCS index %d\n", mcs_index);
return -EINVAL;
}

vif->manual_mcs = mcs_index;
vif->manual_mcs_set = true;
pr_info("vwifi: Set manual MCS %d for dev %s\n", mcs_index, dev->name);

return 0;
}

/* Structure of functions for FullMAC 80211 drivers. Functions implemented
* along with fields/flags in the wiphy structure represent driver features.
Expand All @@ -2170,6 +2324,7 @@ static struct cfg80211_ops vwifi_cfg_ops = {
.get_tx_power = vwifi_get_tx_power,
.join_ibss = vwifi_join_ibss,
.leave_ibss = vwifi_leave_ibss,
.set_bitrate_mask = vwifi_set_bitrate_mask,
};

/* Macro for defining 2GHZ channel array */
Expand Down Expand Up @@ -2223,9 +2378,28 @@ static const struct ieee80211_rate vwifi_supported_rates[] = {
RATE_ENT(360, 0x200), RATE_ENT(480, 0x400), RATE_ENT(540, 0x800),
};

/* Describes supported band of 2GHz. */
static struct ieee80211_supported_band nf_band_2ghz;

static struct ieee80211_supported_band nf_band_2ghz = {
.band = NL80211_BAND_2GHZ,
.channels = vwifi_supported_channels_2ghz,
.n_channels = ARRAY_SIZE(vwifi_supported_channels_2ghz),
.bitrates = vwifi_supported_rates,
.n_bitrates = ARRAY_SIZE(vwifi_supported_rates),
.ht_cap =
{
.ht_supported = true,
.cap = IEEE80211_HT_CAP_SGI_20 | IEEE80211_HT_CAP_GRN_FLD |
IEEE80211_HT_CAP_MAX_AMSDU |
IEEE80211_HT_CAP_SUP_WIDTH_20_40,
.mcs =
{
.rx_mask = {0xff, 0xff, 0xff, 0xff}, /* MCS 0-31 */
.rx_highest = cpu_to_le16(300),
.tx_params = IEEE80211_HT_MCS_TX_DEFINED,
},
.ampdu_factor = IEEE80211_HT_MAX_AMPDU_64K,
.ampdu_density = IEEE80211_HT_MPDU_DENSITY_16,
},
};
/* Describes supported band of 5GHz. */
static struct ieee80211_supported_band nf_band_5ghz;

Expand Down
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