Upgrade to 4.4.50-rt62

[kvmfornfv.git] / kernel / drivers / net / ethernet / renesas / ravb_main.c

diff --git a/kernel/drivers/net/ethernet/renesas/ravb_main.c b/kernel/drivers/net/ethernet/renesas/ravb_main.c
index 467d416..549ad20 100644 (file)
--- 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))