netdev - Re: [PATCH v2 net-next] net: Allow SF devices to be used for ZC DMA

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Message-ID: <aHeJfLYpkmwDvvN8@infradead.org>
Date: Wed, 16 Jul 2025 04:14:04 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Christoph Hellwig <hch@...radead.org>,
	Dragos Tatulea <dtatulea@...dia.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Andrew Lunn <andrew+netdev@...n.ch>, Jens Axboe <axboe@...nel.dk>,
	parav@...dia.com, Cosmin Ratio <cratiu@...dia.com>,
	Tariq Toukan <tariqt@...dia.com>,
	Pavel Begunkov <asml.silence@...il.com>,
	Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, io-uring@...r.kernel.org
Subject: Re: [PATCH v2 net-next] net: Allow SF devices to be used for ZC DMA

On Tue, Jul 15, 2025 at 06:06:49AM -0700, Jakub Kicinski wrote:
> On Mon, 14 Jul 2025 21:39:30 -0700 Christoph Hellwig wrote:
> > > LGTM, but we need a better place for this function. netdevice.h is
> > > included directly by 1.5k files, and indirectly by probably another 5k.
> > > It's not a great place to put random helpers with 2 callers. 
> > > Maybe net/netdev_rx_queue.h and net/core/netdev_rx_queue.c?
> > > I don't think it needs to be a static inline either.  
> > 
> > The whole concept is also buggy.  Trying to get a dma-able device by
> > walking down from an upper level construct like the netdevice can't work
> > reliably.  You'll need to explicitly provide the dma_device using either
> > a method or a pointer to it instead of this guesswork.
> 
> Yeah, I'm pretty sure we'll end up with a method in queue ops.
> But it's not that deep, an easy thing to change.

Why not get this right now instead of adding more of the hacky parent
walking?