netdev - Re: [RFC net-next v3 0/7] devmem/io_uring: allow more flexibility for ZC DMA devices

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Message-ID: <desvj3r3zdziohbm5y3demywumahicutmipcvcpdyjrexccbnu@tdlmdemnijws>
Date: Fri, 15 Aug 2025 15:48:37 +0000
From: Dragos Tatulea <dtatulea@...dia.com>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: almasrymina@...gle.com, asml.silence@...il.com, 
	"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>, Saeed Mahameed <saeedm@...dia.com>, 
	Tariq Toukan <tariqt@...dia.com>, Mark Bloch <mbloch@...dia.com>, 
	Leon Romanovsky <leon@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>, cratiu@...dia.com, 
	parav@...dia.com, Christoph Hellwig <hch@...radead.org>, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, io-uring@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [RFC net-next v3 0/7] devmem/io_uring: allow more flexibility
 for ZC DMA devices

On Fri, Aug 15, 2025 at 08:31:05AM -0700, Stanislav Fomichev wrote:
> On 08/15, Dragos Tatulea wrote:
> > For TCP zerocopy rx (io_uring, devmem), there is an assumption that the
> > parent device can do DMA. However that is not always the case:
> > - Scalable Function netdevs [1] have the DMA device in the grandparent.
> > - For Multi-PF netdevs [2] queues can be associated to different DMA
> >   devices.
> > 
> > The series adds an API for getting the DMA device for a netdev queue.
> > Drivers that have special requirements can implement the newly added
> > queue management op. Otherwise the parent will still be used as before.
> > 
> > This series continues with switching to this API for io_uring zcrx and
> > devmem and adds a ndo_queue_dma_dev op for mlx5.
> > 
> > The last part of the series changes devmem rx bind to get the DMA device
> > per queue and blocks the case when multiple queues use different DMA
> > devices. The tx bind is left as is.
> > 
> > [1] Documentation/networking/device_drivers/ethernet/mellanox/mlx5/switchdev.rst
> > [2] Documentation/networking/multi-pf-netdev.rst
> > 
> > Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
> > 
> > ----
> > Changes sice v2 [3]:
> > - Downgraded to RFC status until consensus is reached.
> > - Implemented more generic approach as discussed during
> >   v2 review.
> > - Refactor devmem to get DMA device for multiple rx queues for
> >   multi PF netdev support.
> > - Renamed series with a more generic name.
> > 
> > Changes since v1 [2]:
> > - Dropped the Fixes tag.
> > - Added more documentation as requeseted.
> > - Renamed the patch title to better reflect its purpose.
> > 
> > Changes since RFC [1]:
> > - 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.
> > 
> > [1] RFC: https://lore.kernel.org/all/20250702172433.1738947-2-dtatulea@nvidia.com/
> > [2]  v1: https://lore.kernel.org/all/20250709124059.516095-2-dtatulea@nvidia.com/
> > [3]  v2: https://lore.kernel.org/all/20250711092634.2733340-2-dtatulea@nvidia.com/
> > ---
> > Dragos Tatulea (7):
> >   queue_api: add support for fetching per queue DMA dev
> 
> [..]
> 
> >   io_uring/zcrx: add support for custom DMA devices
> 
> Did something happen to 2/7? I don't see it in my mailbox and in the
> lore..
I see it in lore:
https://lore.kernel.org/all/20250815110401.2254214-4-dtatulea@nvidia.com

But it seems to have been sent to io-uring ml only and since you were
not CC'ed, I guess it never reached your inbox... I should have
explicitly CC'ed netdev instead of relying on get_maintainers.pl. Will
do it next time.

Thanks,
Dragos