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References: <20201020220639.130696-1-joel@jms.id.au>
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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Wed, 21 Oct 2020 14:40:04 +0200
Message-ID: <CAK8P3a3gz4rMSkvZZ+TPaBx3B1yHXcUVFDdMFQMGUtEi4xXzyg@mail.gmail.com>
Subject: Re: [PATCH] net: ftgmac100: Ensure tx descriptor updates are visible
To:     Joel Stanley <joel@jms.id.au>
Cc:     Jakub Kicinski <kuba@kernel.org>,
        "David S . Miller" <davem@davemloft.net>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Dylan Hung <dylan_hung@aspeedtech.com>,
        Networking <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        linux-aspeed <linux-aspeed@lists.ozlabs.org>
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On Wed, Oct 21, 2020 at 12:39 PM Joel Stanley <joel@jms.id.au> wrote:

>
> diff --git a/drivers/net/ethernet/faraday/ftgmac100.c b/drivers/net/ethernet/faraday/ftgmac100.c
> index 331d4bdd4a67..15cdfeb135b0 100644
> --- a/drivers/net/ethernet/faraday/ftgmac100.c
> +++ b/drivers/net/ethernet/faraday/ftgmac100.c
> @@ -653,6 +653,11 @@ static bool ftgmac100_tx_complete_packet(struct ftgmac100 *priv)
>         ftgmac100_free_tx_packet(priv, pointer, skb, txdes, ctl_stat);
>         txdes->txdes0 = cpu_to_le32(ctl_stat & priv->txdes0_edotr_mask);
>
> +       /* Ensure the descriptor config is visible before setting the tx
> +        * pointer.
> +        */
> +       smp_wmb();
> +
>         priv->tx_clean_pointer = ftgmac100_next_tx_pointer(priv, pointer);
>
>         return true;
> @@ -806,6 +811,11 @@ static netdev_tx_t ftgmac100_hard_start_xmit(struct sk_buff *skb,
>         dma_wmb();
>         first->txdes0 = cpu_to_le32(f_ctl_stat);
>
> +       /* Ensure the descriptor config is visible before setting the tx
> +        * pointer.
> +        */
> +       smp_wmb();
> +

Shouldn't these be paired with smp_rmb() on the reader side?

      Arnd