netdev - Re: [PATCH net] net: Allow non parent devices to be used for ZC DMA

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Message-ID: <020a278f-2fae-4242-b55a-7b4faab37e55@gmail.com>
Date: Wed, 9 Jul 2025 14:50:24 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Dragos Tatulea <dtatulea@...dia.com>, almasrymina@...gle.com,
 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>,
 Simon Horman <horms@...nel.org>, Jens Axboe <axboe@...nel.dk>,
 Simona Vetter <simona.vetter@...ll.ch>, Willem de Bruijn
 <willemb@...gle.com>, Kaiyuan Zhang <kaiyuanz@...gle.com>
Cc: cratiu@...dia.com, parav@...dia.com, Tariq Toukan <tariqt@...dia.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 io-uring@...r.kernel.org
Subject: Re: [PATCH net] net: Allow non parent devices to be used for ZC DMA

On 7/9/25 13:40, Dragos Tatulea wrote:
> For zerocopy (io_uring, devmem), there is an assumption that the
> parent device can do DMA. However that is not always the case:
> ScalableFunction devices have the DMA device in the grandparent.
> 
> This patch adds a helper for getting the DMA device for a netdev from
> its parent or grandparent if necessary. The NULL case is handled in the
> callers.
> 
> devmem and io_uring are updated accordingly to use this helper instead
> of directly using the parent.
> 
> Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
> Fixes: 170aafe35cb9 ("netdev: support binding dma-buf to netdevice")
> Reviewed-by: Tariq Toukan <tariqt@...dia.com>
> ---
> Changes in v1:
> - Upgraded from RFC status.
> - Dropped driver specific bits for generic solution.
> - Implemented single patch as a fix as requested in RFC.
> - Handling of multi-PF netdevs will be handled in a subsequent patch
>    series.
> 
> RFC: https://lore.kernel.org/all/20250702172433.1738947-2-dtatulea@nvidia.com/
I can't say anything about the walking to grand parent part, but
the rest looks good.

Reviewed-by: Pavel Begunkov <asml.silence@...il.com>

-- 
Pavel Begunkov