net: enetc: simplify callers of enetc_rxbd_next

When we iterate through the BDs in the RX ring, the software producer
index (which is already passed by value to enetc_rxbd_next) lags behind,
and we end up with this funny looking "++i == rx_ring->bd_count" check
so that we drag it after us.

Let's pass the software producer index "i" by reference, so that
enetc_rxbd_next can increment it by itself (mod rx_ring->bd_count),
especially since enetc_rxbd_next has to increment the index anyway.
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

@@ -479,13 +479,8 @@ static int enetc_refill_rx_ring(struct enetc_bdr *rx_ring, const int buff_cnt)
 		/* clear 'R" as well */
 		rxbd->r.lstatus = 0;
 
-		rxbd = enetc_rxbd_next(rx_ring, rxbd, i);
-		rx_swbd++;
-		i++;
-		if (unlikely(i == rx_ring->bd_count)) {
-			i = 0;
-			rx_swbd = rx_ring->rx_swbd;
-		}
+		enetc_rxbd_next(rx_ring, &rxbd, &i);
+		rx_swbd = &rx_ring->rx_swbd[i];
 	}
 
 	if (likely(j)) {
@@ -700,9 +695,7 @@ static int enetc_clean_rx_ring(struct enetc_bdr *rx_ring,
 
 		cleaned_cnt++;
 
-		rxbd = enetc_rxbd_next(rx_ring, rxbd, i);
-		if (unlikely(++i == rx_ring->bd_count))
-			i = 0;
+		enetc_rxbd_next(rx_ring, &rxbd, &i);
 
 		if (unlikely(bd_status &
 			     ENETC_RXBD_LSTATUS(ENETC_RXBD_ERR_MASK))) {
@@ -711,9 +704,7 @@ static int enetc_clean_rx_ring(struct enetc_bdr *rx_ring,
 				dma_rmb();
 				bd_status = le32_to_cpu(rxbd->r.lstatus);
 
-				rxbd = enetc_rxbd_next(rx_ring, rxbd, i);
-				if (unlikely(++i == rx_ring->bd_count))
-					i = 0;
+				enetc_rxbd_next(rx_ring, &rxbd, &i);
 			}
 
 			rx_ring->ndev->stats.rx_dropped++;
@@ -736,9 +727,7 @@ static int enetc_clean_rx_ring(struct enetc_bdr *rx_ring,
 
 			cleaned_cnt++;
 
-			rxbd = enetc_rxbd_next(rx_ring, rxbd, i);
-			if (unlikely(++i == rx_ring->bd_count))
-				i = 0;
+			enetc_rxbd_next(rx_ring, &rxbd, &i);
 		}
 
 		rx_byte_cnt += skb->len;

drivers/net/ethernet/freescale/enetc/enetc.h

@@ -121,19 +121,26 @@ static inline union enetc_rx_bd *enetc_rxbd(struct enetc_bdr *rx_ring, int i)
 	return &(((union enetc_rx_bd *)rx_ring->bd_base)[hw_idx]);
 }
 
-static inline union enetc_rx_bd *enetc_rxbd_next(struct enetc_bdr *rx_ring,
-						 union enetc_rx_bd *rxbd,
-						 int i)
+static inline void enetc_rxbd_next(struct enetc_bdr *rx_ring,
+				   union enetc_rx_bd **old_rxbd, int *old_index)
 {
-	rxbd++;
+	union enetc_rx_bd *new_rxbd = *old_rxbd;
+	int new_index = *old_index;
+
+	new_rxbd++;
+
 #ifdef CONFIG_FSL_ENETC_PTP_CLOCK
 	if (rx_ring->ext_en)
-		rxbd++;
+		new_rxbd++;
 #endif
-	if (unlikely(++i == rx_ring->bd_count))
-		rxbd = rx_ring->bd_base;
 
-	return rxbd;
+	if (unlikely(++new_index == rx_ring->bd_count)) {
+		new_rxbd = rx_ring->bd_base;
+		new_index = 0;
+	}
+
+	*old_rxbd = new_rxbd;
+	*old_index = new_index;
 }
 
 static inline union enetc_rx_bd *enetc_rxbd_ext(union enetc_rx_bd *rxbd)