1 files changed, 24 insertions, 3 deletions

diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
index 94b6fb94f8f1..e2d7ce1a85e8 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -802,7 +802,6 @@ static int ravb_rx_gbeth(struct net_device *ndev, int budget, int q)
 	const struct ravb_hw_info *info = priv->info;
 	struct net_device_stats *stats;
 	struct ravb_rx_desc *desc;
-	struct sk_buff *skb;
 	int rx_packets = 0;
 	u8  desc_status;
 	u16 desc_len;
@@ -815,6 +814,8 @@ static int ravb_rx_gbeth(struct net_device *ndev, int budget, int q)
 	stats = &priv->stats[q];
 
 	for (i = 0; i < limit; i++, priv->cur_rx[q]++) {
+		struct sk_buff *skb = NULL;
+
 		entry = priv->cur_rx[q] % priv->num_rx_ring[q];
 		desc = &priv->rx_ring[q].desc[entry];
 		if (rx_packets == budget || desc->die_dt == DT_FEMPTY)
@@ -2210,15 +2211,35 @@ static netdev_tx_t ravb_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 
 		skb_tx_timestamp(skb);
 	}
-	/* Descriptor type must be set after all the above writes */
-	dma_wmb();
+
 	if (num_tx_desc > 1) {
 		desc->die_dt = DT_FEND;
 		desc--;
+		/* When using multi-descriptors, DT_FEND needs to get written
+		 * before DT_FSTART, but the compiler may reorder the memory
+		 * writes in an attempt to optimize the code.
+		 * Use a dma_wmb() barrier to make sure DT_FEND and DT_FSTART
+		 * are written exactly in the order shown in the code.
+		 * This is particularly important for cases where the DMA engine
+		 * is already running when we are running this code. If the DMA
+		 * sees DT_FSTART without the corresponding DT_FEND it will enter
+		 * an error condition.
+		 */
+		dma_wmb();
 		desc->die_dt = DT_FSTART;
 	} else {
+		/* Descriptor type must be set after all the above writes */
+		dma_wmb();
 		desc->die_dt = DT_FSINGLE;
 	}
+
+	/* Before ringing the doorbell we need to make sure that the latest
+	 * writes have been committed to memory, otherwise it could delay
+	 * things until the doorbell is rang again.
+	 * This is in replacement of the read operation mentioned in the HW
+	 * manuals.
+	 */
+	dma_wmb();
 	ravb_modify(ndev, TCCR, TCCR_TSRQ0 << q, TCCR_TSRQ0 << q);
 
 	priv->cur_tx[q] += num_tx_desc;