mt76: mt7921: fix firmware usage of RA info using legacy rates

According to the firmware usage, OFDM rates should fill out bit 6 - 13
while CCK rates should fill out bit 0 - 3 in legacy field of RA info to
make the rate adaption runs propertly. Otherwise, a unicast frame might be
picking up the unsupported rate to send out.

Fixes: 1c099ab4 ("mt76: mt7921: add MCU support")
Reported-by: Joshua Emele <jemele@chromium.org>
Co-developed-by: YN Chen <YN.Chen@mediatek.com>
Signed-off-by: YN Chen <YN.Chen@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.c

@@ -719,6 +719,7 @@ void mt76_connac_mcu_sta_tlv(struct mt76_phy *mphy, struct sk_buff *skb,
 	struct sta_rec_state *state;
 	struct sta_rec_phy *phy;
 	struct tlv *tlv;
+	u16 supp_rates;
 
 	/* starec ht */
 	if (sta->ht_cap.ht_supported) {
@@ -767,7 +768,15 @@ void mt76_connac_mcu_sta_tlv(struct mt76_phy *mphy, struct sk_buff *skb,
 
 	tlv = mt76_connac_mcu_add_tlv(skb, STA_REC_RA, sizeof(*ra_info));
 	ra_info = (struct sta_rec_ra_info *)tlv;
-	ra_info->legacy = cpu_to_le16((u16)sta->supp_rates[band]);
+
+	supp_rates = sta->supp_rates[band];
+	if (band == NL80211_BAND_2GHZ)
+		supp_rates = FIELD_PREP(RA_LEGACY_OFDM, supp_rates >> 4) |
+			     FIELD_PREP(RA_LEGACY_CCK, supp_rates & 0xf);
+	else
+		supp_rates = FIELD_PREP(RA_LEGACY_OFDM, supp_rates);
+
+	ra_info->legacy = cpu_to_le16(supp_rates);
 
 	if (sta->ht_cap.ht_supported)
 		memcpy(ra_info->rx_mcs_bitmask, sta->ht_cap.mcs.rx_mask,

drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.h

@@ -124,6 +124,8 @@ struct sta_rec_state {
 	u8 rsv[1];
 } __packed;
 
+#define RA_LEGACY_OFDM GENMASK(13, 6)
+#define RA_LEGACY_CCK  GENMASK(3, 0)
 #define HT_MCS_MASK_NUM 10
 struct sta_rec_ra_info {
 	__le16 tag;