On Wed, 2 May 2007, Scott Wood wrote:
> Kumar Gala wrote:
> > Why doesn't marking the bdp pointer volatile resolve the issue in
> > gfar_clean_rx_ring() to ensure load ordering?
>
> Because that only addresses compiler reordering (and does so in a rather
> clumsy way -- not all accesses need to be strongly ordered), not hardware
> reordering.
>
> -Scott
>
So what about some thing like this where we do the read only once?
- k
diff --git a/drivers/net/gianfar.c b/drivers/net/gianfar.c
index a06d8d1..9cd7d1e 100644
--- a/drivers/net/gianfar.c
+++ b/drivers/net/gianfar.c
@@ -1438,31 +1438,35 @@ int gfar_clean_rx_ring(struct net_device *dev, int
rx_work_limit)
{
struct rxbd8 *bdp;
struct sk_buff *skb;
- u16 pkt_len;
+ u16 pkt_len, status;
+ u32 bd_info;
int howmany = 0;
struct gfar_private *priv = netdev_priv(dev);
/* Get the first full descriptor */
bdp = priv->cur_rx;
- while (!((bdp->status & RXBD_EMPTY) || (--rx_work_limit < 0))) {
+ bd_info = *bdp;
+
+ status = bd_info >> 16;
+ /* Remove the FCS from the packet length */
+ pkt_len = (bd_info & 0xffff) - 4;
+
+ while (!((status & RXBD_EMPTY) || (--rx_work_limit < 0))) {
skb = priv->rx_skbuff[priv->skb_currx];
- if (!(bdp->status &
+ if (!(status &
(RXBD_LARGE | RXBD_SHORT | RXBD_NONOCTET
| RXBD_CRCERR | RXBD_OVERRUN | RXBD_TRUNCATED))) {
/* Increment the number of packets */
priv->stats.rx_packets++;
howmany++;
- /* Remove the FCS from the packet length */
- pkt_len = bdp->length - 4;
-
gfar_process_frame(dev, skb, pkt_len);
priv->stats.rx_bytes += pkt_len;
} else {
- count_errors(bdp->status, priv);
+ count_errors(status, priv);
if (skb)
dev_kfree_skb_any(skb);
@@ -1480,7 +1484,7 @@ int gfar_clean_rx_ring(struct net_device *dev, int
rx_work_limit)
priv->rx_skbuff[priv->skb_currx] = skb;
/* Update to the next pointer */
- if (bdp->status & RXBD_WRAP)
+ if (status & RXBD_WRAP)
bdp = priv->rx_bd_base;
else
bdp++;
@@ -1490,6 +1494,11 @@ int gfar_clean_rx_ring(struct net_device *dev, int
rx_work_limit)
(priv->skb_currx +
1) & RX_RING_MOD_MASK(priv->rx_ring_size);
+ bd_info = *bdp;
+
+ status = bd_info >> 16;
+ /* Remove the FCS from the packet length */
+ pkt_len = (bd_info & 0xffff) - 4;
}
/* Update the current rxbd pointer to be the next one */
-
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