sh_eth: Ensure proper ordering of descriptor active bit write/read

When submitting a DMA descriptor, the active bit must be written last.
When reading a completed DMA descriptor, the active bit must be read
first.

Add memory barriers to ensure that this ordering is maintained.

Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/renesas/sh_eth.c b/drivers/net/ethernet/renesas/sh_eth.c
index 654b48d1e61a31246bd7838809cb5304954ff76e..5c212a833bcf2df8dee6951dc99bbc9bcc56b321 100644 (file)
--- a/drivers/net/ethernet/renesas/sh_eth.c
+++ b/drivers/net/ethernet/renesas/sh_eth.c
@@ -1410,6 +1410,8 @@ static int sh_eth_txfree(struct net_device *ndev)
                txdesc = &mdp->tx_ring[entry];
                if (txdesc->status & cpu_to_edmac(mdp, TD_TACT))
                        break;
+               /* TACT bit must be checked before all the following reads */
+               rmb();
                /* Free the original skb. */
                if (mdp->tx_skbuff[entry]) {
                        dma_unmap_single(&ndev->dev, txdesc->addr,
@@ -1447,6 +1449,8 @@ static int sh_eth_rx(struct net_device *ndev, u32 intr_status, int *quota)
        limit = boguscnt;
        rxdesc = &mdp->rx_ring[entry];
        while (!(rxdesc->status & cpu_to_edmac(mdp, RD_RACT))) {
+               /* RACT bit must be checked before all the following reads */
+               rmb();
                desc_status = edmac_to_cpu(mdp, rxdesc->status);
                pkt_len = rxdesc->frame_length;
 
@@ -1526,6 +1530,7 @@ static int sh_eth_rx(struct net_device *ndev, u32 intr_status, int *quota)
                        skb_checksum_none_assert(skb);
                        rxdesc->addr = dma_addr;
                }
+               wmb(); /* RACT bit must be set after all the above writes */
                if (entry >= mdp->num_rx_ring - 1)
                        rxdesc->status |=
                                cpu_to_edmac(mdp, RD_RACT | RD_RFP | RD_RDEL);
@@ -2195,6 +2200,7 @@ static int sh_eth_start_xmit(struct sk_buff *skb, struct net_device *ndev)
        }
        txdesc->buffer_length = skb->len;
 
+       wmb(); /* TACT bit must be set after all the above writes */
        if (entry >= mdp->num_tx_ring - 1)
                txdesc->status |= cpu_to_edmac(mdp, TD_TACT | TD_TDLE);
        else