net: axienet: Handle 0 packet receive gracefully
The AXI-DMA rx-delay interrupt can sometimes be triggered when there are 0 outstanding packets received. This is due to the fact that the receive function will greedily consume as many packets as possible on interrupt. So if two packets (with a very particular timing) arrive in succession they will each cause the rx-delay interrupt, but the first interrupt will consume both packets. This means the second interrupt is a 0 packet receive. This is mostly OK, except that the tail pointer register is updated unconditionally on receive. Currently the tail pointer is always set to the current bd-ring descriptor under the assumption that the hardware has moved onto the next descriptor. What this means for length 0 recv is the current descriptor that the hardware is potentially yet to use will be marked as the tail. This causes the hardware to think its run out of descriptors deadlocking the whole rx path. Fixed by updating the tail pointer to the most recent successfully consumed descriptor. Reported-by: NWendy Liang <wendy.liang@xilinx.com> Signed-off-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com> Tested-by: NJason Wu <huanyu@xilinx.com> Acked-by: NMichal Simek <michal.simek@xilinx.com> Signed-off-by: NMichal Simek <michal.simek@xilinx.com> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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