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

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Message-ID: <20250710164903.03a962fc@kernel.org>
Date: Thu, 10 Jul 2025 16:49:03 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Dragos Tatulea <dtatulea@...dia.com>
Cc: <almasrymina@...gle.com>, <asml.silence@...il.com>, Andrew Lunn
 <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, "Eric
 Dumazet" <edumazet@...gle.com>, 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>, <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 Wed, 9 Jul 2025 15:40:57 +0300 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.

Sorry for the silence. I'll reply to Parav on the RFC, I don't think
the question I was asking was answered there.