iwlwifi: mvm: modify the tsf_id master/slave logic

For TSF master/slave synchronization, the FW does not require
exact match in the beacon interval between the master interface
and the slave one, but instead requires that the beacon interval
of one interface is the module of the other.

Modify the tsf_id selection to align with the above.
Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>

drivers/net/wireless/iwlwifi/mvm/mac-ctxt.c

@@ -90,6 +90,7 @@ static void iwl_mvm_mac_tsf_id_iter(void *_data, u8 *mac,
 {
 	struct iwl_mvm_mac_iface_iterator_data *data = _data;
 	struct iwl_mvm_vif *mvmvif = iwl_mvm_vif_from_mac80211(vif);
+	u16 min_bi;
 
 	/* Skip the interface for which we are trying to assign a tsf_id  */
 	if (vif == data->vif)
@@ -114,43 +115,58 @@ static void iwl_mvm_mac_tsf_id_iter(void *_data, u8 *mac,
 	switch (data->vif->type) {
 	case NL80211_IFTYPE_STATION:
 		/*
-		 * The new interface is client, so if the existing one
-		 * we're iterating is an AP, and both interfaces have the
-		 * same beacon interval, the same TSF should be used to
-		 * avoid drift between the new client and existing AP,
-		 * the existing AP will get drift updates from the new
-		 * client context in this case
+		 * The new interface is a client, so if the one we're iterating
+		 * is an AP, and the beacon interval of the AP is a multiple or
+		 * divisor of the beacon interval of the client, the same TSF
+		 * should be used to avoid drift between the new client and
+		 * existing AP. The existing AP will get drift updates from the
+		 * new client context in this case.
 		 */
-		if (vif->type == NL80211_IFTYPE_AP) {
-			if (data->preferred_tsf == NUM_TSF_IDS &&
-			    test_bit(mvmvif->tsf_id, data->available_tsf_ids) &&
-			    (vif->bss_conf.beacon_int ==
-			     data->vif->bss_conf.beacon_int)) {
+		if (vif->type != NL80211_IFTYPE_AP ||
+		    data->preferred_tsf != NUM_TSF_IDS ||
+		    !test_bit(mvmvif->tsf_id, data->available_tsf_ids))
+			break;
+
+		min_bi = min(data->vif->bss_conf.beacon_int,
+			     vif->bss_conf.beacon_int);
+
+		if (!min_bi)
+			break;
+
+		if ((data->vif->bss_conf.beacon_int -
+		     vif->bss_conf.beacon_int) % min_bi == 0) {
 			data->preferred_tsf = mvmvif->tsf_id;
 			return;
 		}
-		}
 		break;
+
 	case NL80211_IFTYPE_AP:
 		/*
-		 * The new interface is AP/GO, so in case both interfaces
-		 * have the same beacon interval, it should get drift
-		 * updates from an existing client or use the same
-		 * TSF as an existing GO. There's no drift between
-		 * TSFs internally but if they used different TSFs
-		 * then a new client MAC could update one of them
-		 * and cause drift that way.
+		 * The new interface is AP/GO, so if its beacon interval is a
+		 * multiple or a divisor of the beacon interval of an existing
+		 * interface, it should get drift updates from an existing
+		 * client or use the same TSF as an existing GO. There's no
+		 * drift between TSFs internally but if they used different
+		 * TSFs then a new client MAC could update one of them and
+		 * cause drift that way.
 		 */
-		if (vif->type == NL80211_IFTYPE_STATION ||
-		    vif->type == NL80211_IFTYPE_AP) {
-			if (data->preferred_tsf == NUM_TSF_IDS &&
-			    test_bit(mvmvif->tsf_id, data->available_tsf_ids) &&
-			    (vif->bss_conf.beacon_int ==
-			     data->vif->bss_conf.beacon_int)) {
+		if ((vif->type != NL80211_IFTYPE_AP &&
+		     vif->type != NL80211_IFTYPE_STATION) ||
+		    data->preferred_tsf != NUM_TSF_IDS ||
+		    !test_bit(mvmvif->tsf_id, data->available_tsf_ids))
+			break;
+
+		min_bi = min(data->vif->bss_conf.beacon_int,
+			     vif->bss_conf.beacon_int);
+
+		if (!min_bi)
+			break;
+
+		if ((data->vif->bss_conf.beacon_int -
+		     vif->bss_conf.beacon_int) % min_bi == 0) {
 			data->preferred_tsf = mvmvif->tsf_id;
 			return;
 		}
-		}
 		break;
 	default:
 		/*