Merge branch 'rework-the-memory-barrier-for-scrq-entry'

Lijun Pan says:

====================
rework the memory barrier for SCRQ entry

This series rework the memory barrier for SCRQ (Sub-Command-Response
Queue) entry.
====================

Link: https://lore.kernel.org/r/20210130011905.1485-1-ljp@linux.ibm.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/ibm/ibmvnic.c

@@ -2444,12 +2444,6 @@ static int ibmvnic_poll(struct napi_struct *napi, int budget)
 
 		if (!pending_scrq(adapter, rx_scrq))
 			break;
-		/* The queue entry at the current index is peeked at above
-		 * to determine that there is a valid descriptor awaiting
-		 * processing. We want to be sure that the current slot
-		 * holds a valid descriptor before reading its contents.
-		 */
-		dma_rmb();
 		next = ibmvnic_next_scrq(adapter, rx_scrq);
 		rx_buff =
 		    (struct ibmvnic_rx_buff *)be64_to_cpu(next->
@@ -2516,7 +2510,6 @@ static int ibmvnic_poll(struct napi_struct *napi, int budget)
 		if (napi_complete_done(napi, frames_processed)) {
 			enable_scrq_irq(adapter, rx_scrq);
 			if (pending_scrq(adapter, rx_scrq)) {
-				rmb();
 				if (napi_reschedule(napi)) {
 					disable_scrq_irq(adapter, rx_scrq);
 					goto restart_poll;
@@ -3189,13 +3182,6 @@ static int ibmvnic_complete_tx(struct ibmvnic_adapter *adapter,
 		int total_bytes = 0;
 		int num_packets = 0;
 
-		/* The queue entry at the current index is peeked at above
-		 * to determine that there is a valid descriptor awaiting
-		 * processing. We want to be sure that the current slot
-		 * holds a valid descriptor before reading its contents.
-		 */
-		dma_rmb();
-
 		next = ibmvnic_next_scrq(adapter, scrq);
 		for (i = 0; i < next->tx_comp.num_comps; i++) {
 			if (next->tx_comp.rcs[i])
@@ -3569,11 +3555,16 @@ static int pending_scrq(struct ibmvnic_adapter *adapter,
 			struct ibmvnic_sub_crq_queue *scrq)
 {
 	union sub_crq *entry = &scrq->msgs[scrq->cur];
+	int rc;
 
-	if (entry->generic.first & IBMVNIC_CRQ_CMD_RSP)
-		return 1;
-	else
-		return 0;
+	rc = !!(entry->generic.first & IBMVNIC_CRQ_CMD_RSP);
+
+	/* Ensure that the SCRQ valid flag is loaded prior to loading the
+	 * contents of the SCRQ descriptor
+	 */
+	dma_rmb();
+
+	return rc;
 }
 
 static union sub_crq *ibmvnic_next_scrq(struct ibmvnic_adapter *adapter,
@@ -3592,8 +3583,8 @@ static union sub_crq *ibmvnic_next_scrq(struct ibmvnic_adapter *adapter,
 	}
 	spin_unlock_irqrestore(&scrq->lock, flags);
 
-	/* Ensure that the entire buffer descriptor has been
-	 * loaded before reading its contents
+	/* Ensure that the SCRQ valid flag is loaded prior to loading the
+	 * contents of the SCRQ descriptor
 	 */
 	dma_rmb();