ibmvnic: rework to ensure SCRQ entry reads are properly ordered

Move the dma_rmb() between pending_scrq() and ibmvnic_next_scrq()
into the end of pending_scrq() to save the duplicated code since
this dma_rmb will be used 3 times.

Signed-off-by: Lijun Pan <[email protected]>
Acked-by: Thomas Falcon <[email protected]>
Signed-off-by: Jakub Kicinski <[email protected]>

Author: Lijun Pan

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->
@@ -3189,13 +3183,6 @@ 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 +3556,16 @@ 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 +3584,8 @@ 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();