net: enetc: consume the error RX buffer descriptors in a dedicated function

We can and should check the RX BD errors before starting to build the
skb. The only apparent reason why things are done in this backwards
order is to spare one call to enetc_rxbd_next.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/enetc/enetc.c

@@ -605,6 +605,28 @@ static void enetc_add_rx_buff_to_skb(struct enetc_bdr *rx_ring, int i,
 	enetc_put_rx_buff(rx_ring, rx_swbd);
 }
 
+static bool enetc_check_bd_errors_and_consume(struct enetc_bdr *rx_ring,
+					      u32 bd_status,
+					      union enetc_rx_bd **rxbd, int *i)
+{
+	if (likely(!(bd_status & ENETC_RXBD_LSTATUS(ENETC_RXBD_ERR_MASK))))
+		return false;
+
+	enetc_rxbd_next(rx_ring, rxbd, i);
+
+	while (!(bd_status & ENETC_RXBD_LSTATUS_F)) {
+		dma_rmb();
+		bd_status = le32_to_cpu((*rxbd)->r.lstatus);
+
+		enetc_rxbd_next(rx_ring, rxbd, i);
+	}
+
+	rx_ring->ndev->stats.rx_dropped++;
+	rx_ring->ndev->stats.rx_errors++;
+
+	return true;
+}
+
 #define ENETC_RXBD_BUNDLE 16 /* # of BDs to update at once */
 
 static int enetc_clean_rx_ring(struct enetc_bdr *rx_ring,
@@ -634,6 +656,11 @@ static int enetc_clean_rx_ring(struct enetc_bdr *rx_ring,
 
 		enetc_wr_reg_hot(rx_ring->idr, BIT(rx_ring->index));
 		dma_rmb(); /* for reading other rxbd fields */
+
+		if (enetc_check_bd_errors_and_consume(rx_ring, bd_status,
+						      &rxbd, &i))
+			break;
+
 		size = le16_to_cpu(rxbd->r.buf_len);
 		skb = enetc_map_rx_buff_to_skb(rx_ring, i, size);
 		if (!skb)
@@ -645,22 +672,6 @@ static int enetc_clean_rx_ring(struct enetc_bdr *rx_ring,
 
 		enetc_rxbd_next(rx_ring, &rxbd, &i);
 
-		if (unlikely(bd_status &
-			     ENETC_RXBD_LSTATUS(ENETC_RXBD_ERR_MASK))) {
-			dev_kfree_skb(skb);
-			while (!(bd_status & ENETC_RXBD_LSTATUS_F)) {
-				dma_rmb();
-				bd_status = le32_to_cpu(rxbd->r.lstatus);
-
-				enetc_rxbd_next(rx_ring, &rxbd, &i);
-			}
-
-			rx_ring->ndev->stats.rx_dropped++;
-			rx_ring->ndev->stats.rx_errors++;
-
-			break;
-		}
-
 		/* not last BD in frame? */
 		while (!(bd_status & ENETC_RXBD_LSTATUS_F)) {
 			bd_status = le32_to_cpu(rxbd->r.lstatus);