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>

diff --git a/drivers/net/ethernet/cadence/macb.c b/drivers/net/ethernet/cadence/macb.c
index 3e13aa31548a4ad6adf26849984abab8c0f4a25e..e9daa072ebb4f2c03af453255a9c374bde6ff47c 100644 (file)
--- a/drivers/net/ethernet/cadence/macb.c
+++ b/drivers/net/ethernet/cadence/macb.c
@@ -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++;