iwlwifi: mvm: don't send the IWL_MVM_RXQ_NSSN_SYNC notif to Rx queues

The purpose of this was to keep all the queues updated with
the Rx sequence numbers because unlikely yet possible
situations where queues can't understand if a specific
packet needs to be dropped or not.

Unfortunately, it was reported that this caused issues in
our DMA engine. We don't fully understand how this is related,
but this is being currently debugged. For now, just don't send
this notification to the Rx queues. This de-facto reverts my
commit 3c514bf8:

iwlwifi: mvm: add a loose synchronization of the NSSN across Rx queues

This issue was reported here:
https://bugzilla.kernel.org/show_bug.cgi?id=204873
https://bugzilla.kernel.org/show_bug.cgi?id=205001
and others maybe.

Fixes: 3c514bf8 ("iwlwifi: mvm: add a loose synchronization of the NSSN across Rx queues")
CC: <stable@vger.kernel.org> # 5.3+
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/intel/iwlwifi/mvm/constants.h

@@ -154,5 +154,6 @@
 #define IWL_MVM_D3_DEBUG			false
 #define IWL_MVM_USE_TWT				false
 #define IWL_MVM_AMPDU_CONSEC_DROPS_DELBA	10
+#define IWL_MVM_USE_NSSN_SYNC			0
 
 #endif /* __MVM_CONSTANTS_H */

drivers/net/wireless/intel/iwlwifi/mvm/rxmq.c

@@ -514,14 +514,17 @@ static bool iwl_mvm_is_sn_less(u16 sn1, u16 sn2, u16 buffer_size)
 
 static void iwl_mvm_sync_nssn(struct iwl_mvm *mvm, u8 baid, u16 nssn)
 {
-	struct iwl_mvm_rss_sync_notif notif = {
-		.metadata.type = IWL_MVM_RXQ_NSSN_SYNC,
-		.metadata.sync = 0,
-		.nssn_sync.baid = baid,
-		.nssn_sync.nssn = nssn,
-	};
-
-	iwl_mvm_sync_rx_queues_internal(mvm, (void *)&notif, sizeof(notif));
+	if (IWL_MVM_USE_NSSN_SYNC) {
+		struct iwl_mvm_rss_sync_notif notif = {
+			.metadata.type = IWL_MVM_RXQ_NSSN_SYNC,
+			.metadata.sync = 0,
+			.nssn_sync.baid = baid,
+			.nssn_sync.nssn = nssn,
+		};
+
+		iwl_mvm_sync_rx_queues_internal(mvm, (void *)&notif,
+						sizeof(notif));
+	}
 }
 
 #define RX_REORDER_BUF_TIMEOUT_MQ (HZ / 10)