Re: [RFC net-next v3 0/7] devmem/io_uring: allow more flexibility for ZC DMA devices
From: Stanislav Fomichev
Date: Fri Aug 15 2025 - 11:32:58 EST
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@xxxxxxxxxx>
>
> ----
> 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@xxxxxxxxxx/
> [2] v1: https://lore.kernel.org/all/20250709124059.516095-2-dtatulea@xxxxxxxxxx/
> [3] v2: https://lore.kernel.org/all/20250711092634.2733340-2-dtatulea@xxxxxxxxxx/
> ---
> 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..