netdev - Re: [PATCH net] net: stmmac: Sync RX Buffer upon allocation

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Date:   Tue, 30 Jul 2019 11:17:39 -0300
From:   Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
To:     Jose Abreu <Jose.Abreu@...opsys.com>
Cc:     Networking <netdev@...r.kernel.org>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jon Hunter <jonathanh@...dia.com>
Subject: Re: [PATCH net] net: stmmac: Sync RX Buffer upon allocation

On Tue, 30 Jul 2019 at 10:57, Jose Abreu <Jose.Abreu@...opsys.com> wrote:
>
> With recent changes that introduced support for Page Pool in stmmac, Jon
> reported that NFS boot was no longer working on an ARM64 based platform
> that had the IP behind an IOMMU.
>
> As Page Pool API does not guarantee DMA syncing because of the use of
> DMA_ATTR_SKIP_CPU_SYNC flag, we have to explicit sync the whole buffer upon
> re-allocation because we are always re-using same pages.
>
> In fact, ARM64 code invalidates the DMA area upon two situations [1]:
>         - sync_single_for_cpu(): Invalidates if direction != DMA_TO_DEVICE
>         - sync_single_for_device(): Invalidates if direction == DMA_FROM_DEVICE
>
> So, as we must invalidate both the current RX buffer and the newly allocated
> buffer we propose this fix.
>
> [1] arch/arm64/mm/cache.S
>
> Reported-by: Jon Hunter <jonathanh@...dia.com>
> Tested-by: Jon Hunter <jonathanh@...dia.com>
> Fixes: 2af6106ae949 ("net: stmmac: Introducing support for Page Pool")
> Signed-off-by: Jose Abreu <joabreu@...opsys.com>

Thanks a lot for the bug hunt and the fix. This fixes NFS mounting
on my RK3288 and RK3399 boards.

Tested-by: Ezequiel Garcia <ezequiel@...labora.com>