ath9k: fix transmitting to stations in dynamic SMPS mode

When transmitting to a receiver in dynamic SMPS mode, all transmissions that
use multiple spatial streams need to be sent using CTS-to-self or RTS/CTS to
give the receiver's extra chains some time to wake up.
This fixes the tx rate getting stuck at <= MCS7 for some clients, especially
Intel ones, which make aggressive use of SMPS.

Cc: stable@vger.kernel.org
Reported-by: Martin Kennedy <hurricos@gmail.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210214184911.96702-1-nbd@nbd.name

drivers/net/wireless/ath/ath9k/ath9k.h

@@ -177,7 +177,8 @@ struct ath_frame_info {
 	s8 txq;
 	u8 keyix;
 	u8 rtscts_rate;
-	u8 retries : 7;
+	u8 retries : 6;
+	u8 dyn_smps : 1;
 	u8 baw_tracked : 1;
 	u8 tx_power;
 	enum ath9k_key_type keytype:2;

drivers/net/wireless/ath/ath9k/xmit.c

@@ -1271,6 +1271,11 @@ static void ath_buf_set_rate(struct ath_softc *sc, struct ath_buf *bf,
 				 is_40, is_sgi, is_sp);
 			if (rix < 8 && (tx_info->flags & IEEE80211_TX_CTL_STBC))
 				info->rates[i].RateFlags |= ATH9K_RATESERIES_STBC;
+			if (rix >= 8 && fi->dyn_smps) {
+				info->rates[i].RateFlags |=
+					ATH9K_RATESERIES_RTS_CTS;
+				info->flags |= ATH9K_TXDESC_CTSENA;
+			}
 
 			info->txpower[i] = ath_get_rate_txpower(sc, bf, rix,
 								is_40, false);
@@ -2114,6 +2119,7 @@ static void setup_frame_info(struct ieee80211_hw *hw,
 		fi->keyix = an->ps_key;
 	else
 		fi->keyix = ATH9K_TXKEYIX_INVALID;
+	fi->dyn_smps = sta && sta->smps_mode == IEEE80211_SMPS_DYNAMIC;
 	fi->keytype = keytype;
 	fi->framelen = framelen;
 	fi->tx_power = txpower;