ath10k: improve 11b coex

Some firmware revisions need peer phymode to be
specified as MODE_11B when associating as station
to a 11b AP. Otherwise they can starve other
stations.
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath10k/mac.c

@@ -1416,6 +1416,12 @@ static void ath10k_peer_assoc_h_qos(struct ath10k *ar,
 	}
 }
 
+static bool ath10k_mac_sta_has_11g_rates(struct ieee80211_sta *sta)
+{
+	/* First 4 rates in ath10k_rates are CCK (11b) rates. */
+	return sta->supp_rates[IEEE80211_BAND_2GHZ] >> 4;
+}
+
 static void ath10k_peer_assoc_h_phymode(struct ath10k *ar,
 					struct ieee80211_vif *vif,
 					struct ieee80211_sta *sta,
@@ -1430,8 +1436,10 @@ static void ath10k_peer_assoc_h_phymode(struct ath10k *ar,
 				phymode = MODE_11NG_HT40;
 			else
 				phymode = MODE_11NG_HT20;
-		} else {
+		} else if (ath10k_mac_sta_has_11g_rates(sta)) {
 			phymode = MODE_11G;
+		} else {
+			phymode = MODE_11B;
 		}
 
 		break;
@@ -4724,6 +4732,9 @@ static const struct ieee80211_channel ath10k_5ghz_channels[] = {
 	CHAN5G(165, 5825, 0),
 };
 
+/* Note: Be careful if you re-order these. There is code which depends on this
+ * ordering.
+ */
 static struct ieee80211_rate ath10k_rates[] = {
 	/* CCK */
 	RATETAB_ENT(10,  0x82, 0),