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net: macb: Fix race between HW and driver 

Under "heavy" RX load, the driver cannot handle the descriptors fast
enough. In detail, when a descriptor is consumed, its used flag is
cleared and once the RX budget is consumed all descriptors with a
cleared used flag are prepared to receive more data. Under load though,
the HW may constantly receive more data and use those descriptors with a
cleared used flag before they are actually prepared for next usage.

The head and tail pointers into the RX-ring should always be valid and
we can omit clearing and checking of the used flag.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Soren Brinkmann 2014-05-04 15:43:02 -07:00 committed by David S. Miller
parent 504ad98df3
commit c8ea5a22bd
1 changed files with 0 additions and 10 deletions
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10
drivers/net/ethernet/cadence/macb.c
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@ -599,25 +599,16 @@ static void gem_rx_refill(struct macb *bp)
{
unsigned int entry;
struct sk_buff *skb;
struct macb_dma_desc *desc;
dma_addr_t paddr;
while (CIRC_SPACE(bp->rx_prepared_head, bp->rx_tail, RX_RING_SIZE) > 0) {
u32 addr, ctrl;
entry = macb_rx_ring_wrap(bp->rx_prepared_head);
desc = &bp->rx_ring[entry];
/* Make hw descriptor updates visible to CPU */
rmb();
addr = desc->addr;
ctrl = desc->ctrl;
bp->rx_prepared_head++;
if ((addr & MACB_BIT(RX_USED)))
continue;
if (bp->rx_skbuff[entry] == NULL) {
/* allocate sk_buff for this free entry in ring */
skb = netdev_alloc_skb(bp->dev, bp->rx_buffer_size);
@ -698,7 +689,6 @@ static int gem_rx(struct macb *bp, int budget)
if (!(addr & MACB_BIT(RX_USED)))
break;
desc->addr &= ~MACB_BIT(RX_USED);
bp->rx_tail++;
count++;