X-Git-Url: https://gerrit.opnfv.org/gerrit/gitweb?a=blobdiff_plain;f=kernel%2Fdrivers%2Fnet%2Fethernet%2Frenesas%2Fravb_main.c;fp=kernel%2Fdrivers%2Fnet%2Fethernet%2Frenesas%2Fravb_main.c;h=549ad2018e7f7d045310389e89cfc7fb3fc0922d;hb=52f993b8e89487ec9ee15a7fb4979e0f09a45b27;hp=467d41698fd534e724d53ce03e35091bd01cdcdb;hpb=c189ccac5702322ed843fe17057035b7222a59b6;p=kvmfornfv.git

diff --git a/kernel/drivers/net/ethernet/renesas/ravb_main.c b/kernel/drivers/net/ethernet/renesas/ravb_main.c
index 467d41698..549ad2018 100644
--- a/kernel/drivers/net/ethernet/renesas/ravb_main.c
+++ b/kernel/drivers/net/ethernet/renesas/ravb_main.c
@@ -1330,6 +1330,19 @@ static netdev_tx_t ravb_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 	buffer = PTR_ALIGN(priv->tx_align[q], DPTR_ALIGN) +
 		 entry / NUM_TX_DESC * DPTR_ALIGN;
 	len = PTR_ALIGN(skb->data, DPTR_ALIGN) - skb->data;
+	/* Zero length DMA descriptors are problematic as they seem to
+	 * terminate DMA transfers. Avoid them by simply using a length of
+	 * DPTR_ALIGN (4) when skb data is aligned to DPTR_ALIGN.
+	 *
+	 * As skb is guaranteed to have at least ETH_ZLEN (60) bytes of
+	 * data by the call to skb_put_padto() above this is safe with
+	 * respect to both the length of the first DMA descriptor (len)
+	 * overflowing the available data and the length of the second DMA
+	 * descriptor (skb->len - len) being negative.
+	 */
+	if (len == 0)
+		len = DPTR_ALIGN;
+
 	memcpy(buffer, skb->data, len);
 	dma_addr = dma_map_single(ndev->dev.parent, buffer, len, DMA_TO_DEVICE);
 	if (dma_mapping_error(ndev->dev.parent, dma_addr))