netdev - Re: [PATCH net v1] net: stmmac: Apply new page pool parameters when SPH is enabled

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Message-ID: <8fc7c79d-ace8-4e05-acef-1699ee6c4158@nvidia.com>
Date: Fri, 7 Feb 2025 13:41:49 +0000
From: Jon Hunter <jonathanh@...dia.com>
To: Furong Xu <0x1207@...il.com>, netdev@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>, xfr@...look.com,
 Brad Griffis <bgriffis@...dia.com>, Ido Schimmel <idosch@...sch.org>,
 "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH net v1] net: stmmac: Apply new page pool parameters when
 SPH is enabled

Hi Furong,

On 07/02/2025 08:56, Furong Xu wrote:
> Commit df542f669307 ("net: stmmac: Switch to zero-copy in
> non-XDP RX path") makes DMA write received frame into buffer at offset
> of NET_SKB_PAD and sets page pool parameters to sync from offset of
> NET_SKB_PAD. But when Header Payload Split is enabled, the header is
> written at offset of NET_SKB_PAD, while the payload is written at
> offset of zero. Uncorrect offset parameter for the payload breaks dma
> coherence [1] since both CPU and DMA touch the page buffer from offset
> of zero which is not handled by the page pool sync parameter.
> 
> And in case the DMA cannot split the received frame, for example,
> a large L2 frame, pp_params.max_len should grow to match the tail
> of entire frame.
> 
> [1] https://lore.kernel.org/netdev/d465f277-bac7-439f-be1d-9a47dfe2d951@nvidia.com/
> 
> Reported-by: Jon Hunter <jonathanh@...dia.com>
> Reported-by: Brad Griffis <bgriffis@...dia.com>
> Suggested-by: Ido Schimmel <idosch@...sch.org>
> Fixes: df542f669307 ("net: stmmac: Switch to zero-copy in non-XDP RX path")
> Signed-off-by: Furong Xu <0x1207@...il.com>
> ---
>   drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index b34ebb916b89..c0ae7db96f46 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -2094,6 +2094,11 @@ static int __alloc_dma_rx_desc_resources(struct stmmac_priv *priv,
>   	pp_params.offset = stmmac_rx_offset(priv);
>   	pp_params.max_len = dma_conf->dma_buf_sz;
>   
> +	if (priv->sph) {
> +		pp_params.offset = 0;
> +		pp_params.max_len += stmmac_rx_offset(priv);
> +	}
> +
>   	rx_q->page_pool = page_pool_create(&pp_params);
>   	if (IS_ERR(rx_q->page_pool)) {
>   		ret = PTR_ERR(rx_q->page_pool);

Thanks for sending this. I can confirm that it fixes the issue we are 
seeing and so ...

Tested-by: Jon Hunter <jonathanh@...dia.com>

Cheers
Jon

-- 
nvpublic