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Date: Mon, 19 Oct 2020 08:57:03 +0000 From: Joel Stanley <joel@....id.au> To: Dylan Hung <dylan_hung@...eedtech.com>, Benjamin Herrenschmidt <benh@...nel.crashing.org> Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Po-Yu Chuang <ratbert@...aday-tech.com>, linux-aspeed <linux-aspeed@...ts.ozlabs.org>, OpenBMC Maillist <openbmc@...ts.ozlabs.org>, BMC-SW <BMC-SW@...eedtech.com> Subject: Re: [PATCH] net: ftgmac100: Fix missing TX-poll issue On Mon, 19 Oct 2020 at 07:39, Dylan Hung <dylan_hung@...eedtech.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@...eedtech.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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