mac80211: handle S1G low rates

S1G doesn't have legacy (sband->bitrates) rates, only MCS.
For now, just send a frame at MCS 0 if a low rate is
requested. Note we also redefine (since we're out of TX
flags) TX_RC_VHT_MCS as TX_RC_S1G_MCS to indicate an S1G
MCS. This is probably OK as VHT MCS is not valid on S1G
band and vice versa.
Signed-off-by: Thomas Pedersen <thomas@adapt-ip.com>
Link: https://lore.kernel.org/r/20200922022818.15855-12-thomas@adapt-ip.comSigned-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -833,6 +833,8 @@ enum mac80211_tx_info_flags {
 
 #define IEEE80211_TX_CTL_STBC_SHIFT		23
 
+#define IEEE80211_TX_RC_S1G_MCS IEEE80211_TX_RC_VHT_MCS
+
 /**
  * enum mac80211_tx_control_flags - flags to describe transmit control
  *

net/mac80211/rate.c

@@ -266,10 +266,15 @@ void ieee80211_check_rate_mask(struct ieee80211_sub_if_data *sdata)
 	if (WARN_ON(!sdata->vif.bss_conf.chandef.chan))
 		return;
 
+	band = sdata->vif.bss_conf.chandef.chan->band;
+	if (band == NL80211_BAND_S1GHZ) {
+		/* TODO */
+		return;
+	}
+
 	if (WARN_ON_ONCE(!basic_rates))
 		return;
 
-	band = sdata->vif.bss_conf.chandef.chan->band;
 	user_mask = sdata->rc_rateidx_mask[band];
 	sband = local->hw.wiphy->bands[band];
 
@@ -296,21 +301,29 @@ static bool rc_no_data_or_no_ack_use_min(struct ieee80211_tx_rate_control *txrc)
 		!ieee80211_is_data(fc);
 }
 
-static void rc_send_low_basicrate(s8 *idx, u32 basic_rates,
+static void rc_send_low_basicrate(struct ieee80211_tx_rate *rate,
+				  u32 basic_rates,
 				  struct ieee80211_supported_band *sband)
 {
 	u8 i;
 
+	if (sband->band == NL80211_BAND_S1GHZ) {
+		/* TODO */
+		rate->flags |= IEEE80211_TX_RC_S1G_MCS;
+		rate->idx = 0;
+		return;
+	}
+
 	if (basic_rates == 0)
 		return; /* assume basic rates unknown and accept rate */
-	if (*idx < 0)
+	if (rate->idx < 0)
 		return;
-	if (basic_rates & (1 << *idx))
+	if (basic_rates & (1 << rate->idx))
 		return; /* selected rate is a basic rate */
 
-	for (i = *idx + 1; i <= sband->n_bitrates; i++) {
+	for (i = rate->idx + 1; i <= sband->n_bitrates; i++) {
 		if (basic_rates & (1 << i)) {
-			*idx = i;
+			rate->idx = i;
 			return;
 		}
 	}
@@ -328,6 +341,12 @@ static void __rate_control_send_low(struct ieee80211_hw *hw,
 	u32 rate_flags =
 		ieee80211_chandef_rate_flags(&hw->conf.chandef);
 
+	if (sband->band == NL80211_BAND_S1GHZ) {
+		info->control.rates[0].flags |= IEEE80211_TX_RC_S1G_MCS;
+		info->control.rates[0].idx = 0;
+		return;
+	}
+
 	if ((sband->band == NL80211_BAND_2GHZ) &&
 	    (info->flags & IEEE80211_TX_CTL_NO_CCK_RATE))
 		rate_flags |= IEEE80211_RATE_ERP_G;
@@ -388,7 +407,7 @@ static bool rate_control_send_low(struct ieee80211_sta *pubsta,
 		}
 
 		if (use_basicrate)
-			rc_send_low_basicrate(&info->control.rates[0].idx,
+			rc_send_low_basicrate(&info->control.rates[0],
 					      txrc->bss_conf->basic_rates,
 					      sband);