linux-kernel - Re: [PATCH net-next] stmmac: align RX buffers

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Date:   Thu, 12 Aug 2021 10:48:03 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Matteo Croce <mcroce@...ux.microsoft.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Drew Fustini <drew@...gleboard.org>,
        Emil Renner Berthing <kernel@...il.dk>,
        Jon Hunter <jonathanh@...dia.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH net-next] stmmac: align RX buffers



On 8/11/21 4:16 PM, Marc Zyngier wrote:
> On Wed, 11 Aug 2021 13:53:59 +0100,
> Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>> Are you sure you do not need to adjust stmmac_set_bfsize(), 
>> stmmac_rx_buf1_len() and stmmac_rx_buf2_len() ?
>>
>> Presumably DEFAULT_BUFSIZE also want to be increased by NET_SKB_PAD
>>
>> Patch for stmmac_rx_buf1_len() :
>>
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> index 7b8404a21544cf29668e8a14240c3971e6bce0c3..041a74e7efca3436bfe3e17f972dd156173957a9 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> @@ -4508,12 +4508,12 @@ static unsigned int stmmac_rx_buf1_len(struct stmmac_priv *priv,
>>  
>>         /* First descriptor, not last descriptor and not split header */
>>         if (status & rx_not_ls)
>> -               return priv->dma_buf_sz;
>> +               return priv->dma_buf_sz - NET_SKB_PAD - NET_IP_ALIGN;
>>  
>>         plen = stmmac_get_rx_frame_len(priv, p, coe);
>>  
>>         /* First descriptor and last descriptor and not split header */
>> -       return min_t(unsigned int, priv->dma_buf_sz, plen);
>> +       return min_t(unsigned int, priv->dma_buf_sz - NET_SKB_PAD - NET_IP_ALIGN, plen);
>>  }
>>  
>>  static unsigned int stmmac_rx_buf2_len(struct stmmac_priv *priv,
> 
> Feels like a major deficiency of the original patch. Happy to test a
> more complete patch if/when you have one.

I wont have time in the immediate future.

Matteo, if you do not work on a fix, I suggest we revert
 a955318fe67ec0d962760b5ee58e74bffaf649b8 stmmac: align RX buffers

before a more polished version can be submitted.