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From: Joel Stanley <joel@jms.id.au>
To: Dylan Hung <dylan_hung@aspeedtech.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: "David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	netdev@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Po-Yu Chuang <ratbert@faraday-tech.com>,
	linux-aspeed <linux-aspeed@lists.ozlabs.org>,
	OpenBMC Maillist <openbmc@lists.ozlabs.org>,
	BMC-SW <BMC-SW@aspeedtech.com>
Subject: Re: [PATCH] net: ftgmac100: Fix missing TX-poll issue
Date: Mon, 19 Oct 2020 08:57:03 +0000	[thread overview]
Message-ID: <CACPK8Xfn+Gn0PHCfhX-vgLTA6e2=RT+D+fnLF67_1j1iwqh7yg@mail.gmail.com> (raw)
In-Reply-To: <20201019073908.32262-1-dylan_hung@aspeedtech.com>

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
>

WARNING: multiple messages have this Message-ID (diff)
From: Joel Stanley <joel@jms.id.au>
To: Dylan Hung <dylan_hung@aspeedtech.com>,
	 Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: BMC-SW <BMC-SW@aspeedtech.com>,
	Po-Yu Chuang <ratbert@faraday-tech.com>,
	linux-aspeed <linux-aspeed@lists.ozlabs.org>,
	netdev@vger.kernel.org,
	OpenBMC Maillist <openbmc@lists.ozlabs.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Jakub Kicinski <kuba@kernel.org>,
	"David S . Miller" <davem@davemloft.net>
Subject: Re: [PATCH] net: ftgmac100: Fix missing TX-poll issue
Date: Mon, 19 Oct 2020 08:57:03 +0000	[thread overview]
Message-ID: <CACPK8Xfn+Gn0PHCfhX-vgLTA6e2=RT+D+fnLF67_1j1iwqh7yg@mail.gmail.com> (raw)
In-Reply-To: <20201019073908.32262-1-dylan_hung@aspeedtech.com>

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
>

  reply	other threads:[~2020-10-19  8:57 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-19  7:39 [PATCH] net: ftgmac100: Fix missing TX-poll issue Dylan Hung
2020-10-19  7:39 ` Dylan Hung
2020-10-19  8:57 ` Joel Stanley [this message]
2020-10-19  8:57   ` Joel Stanley
2020-10-19  9:19   ` Dylan Hung
2020-10-19  9:19     ` Dylan Hung
2020-10-19 19:00   ` Jakub Kicinski
2020-10-19 19:00     ` Jakub Kicinski
2020-10-19 23:23     ` Benjamin Herrenschmidt
2020-10-19 23:23       ` Benjamin Herrenschmidt
2020-10-20  2:57       ` Jakub Kicinski
2020-10-20  2:57         ` Jakub Kicinski
2020-10-20  6:15         ` Benjamin Herrenschmidt
2020-10-20  6:15           ` Benjamin Herrenschmidt
2020-10-20 17:24           ` Jakub Kicinski
2020-10-20 17:24             ` Jakub Kicinski
2020-10-20  6:14     ` Dylan Hung
2020-10-20  6:14       ` Dylan Hung
2020-10-20 13:15       ` David Laight
2020-10-20 13:15         ` David Laight
2020-10-20 22:05         ` Benjamin Herrenschmidt
2020-10-20 22:05           ` Benjamin Herrenschmidt
2020-10-20 19:49       ` Arnd Bergmann
2020-10-20 22:10         ` Benjamin Herrenschmidt
2020-10-20 22:10           ` Benjamin Herrenschmidt
2020-10-20 22:25           ` Andrew Jeffery
2020-10-23 13:08             ` Dylan Hung
2020-10-26 22:21               ` Benjamin Herrenschmidt
2020-10-27  2:18                 ` Joel Stanley
2020-10-27  2:18                   ` Joel Stanley
2020-10-21  7:16           ` Arnd Bergmann
2020-10-21 12:11             ` Arnd Bergmann
2020-10-21 12:11               ` Arnd Bergmann
2020-10-22  7:40               ` Benjamin Herrenschmidt
2020-10-22  7:40                 ` Benjamin Herrenschmidt
2020-10-23  8:39                 ` Arnd Bergmann
2020-10-23  8:39                   ` Arnd Bergmann

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