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Commit c8ea5a22 authored by Soren Brinkmann's avatar Soren Brinkmann Committed by David S. Miller
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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: default avatarSoren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 504ad98d

drivers/net/ethernet/cadence/macb.c

+0 −10
Original line number Diff line number Diff line
@@ -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++;