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    SubjectRe: [PATCH] net: ftgmac100: Fix missing TX-poll issue
    On Mon, 19 Oct 2020 at 07:39, Dylan Hung <dylan_hung@aspeedtech.com> wrote:
    >
    > The cpu accesses the register and the memory via different bus/path on
    > aspeed soc. So we can not guarantee that the tx-poll command

    Just the 2600, or other versions too?

    > (register access) is always behind the tx descriptor (memory). In other
    > words, the HW may start working even the data is not yet ready. By

    even if the

    > adding a dummy read after the last data write, we can ensure the data
    > are pushed to the memory, then guarantee the processing sequence
    >
    > Signed-off-by: Dylan Hung <dylan_hung@aspeedtech.com>
    > ---
    > drivers/net/ethernet/faraday/ftgmac100.c | 3 ++-
    > 1 file changed, 2 insertions(+), 1 deletion(-)
    >
    > diff --git a/drivers/net/ethernet/faraday/ftgmac100.c b/drivers/net/ethernet/faraday/ftgmac100.c
    > index 00024dd41147..9a99a87f29f3 100644
    > --- a/drivers/net/ethernet/faraday/ftgmac100.c
    > +++ b/drivers/net/ethernet/faraday/ftgmac100.c
    > @@ -804,7 +804,8 @@ static netdev_tx_t ftgmac100_hard_start_xmit(struct sk_buff *skb,
    > * before setting the OWN bit on the first descriptor.
    > */
    > dma_wmb();
    > - first->txdes0 = cpu_to_le32(f_ctl_stat);
    > + WRITE_ONCE(first->txdes0, cpu_to_le32(f_ctl_stat));
    > + READ_ONCE(first->txdes0);

    I understand what you're trying to do here, but I'm not sure that this
    is the correct way to go about it.

    It does cause the compiler to produce a store and then a load.

    >
    > /* Update next TX pointer */
    > priv->tx_pointer = pointer;
    > --
    > 2.17.1
    >

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