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Date: Mon, 16 Mar 2026 21:44:19 +0200
From: Leon Romanovsky <leon@kernel.org>
To: Joe Damato <joe@dama.to>
Cc: netdev@vger.kernel.org, michael.chan@broadcom.com,
	pavan.chebbi@broadcom.com, linux-kernel@vger.kernel.org,
	Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: [RFC net-next v2 00/12] Add TSO map-once DMA helpers and bnxt SW
 USO support
Message-ID: <20260316194419.GH61385@unreal>
References: <20260312223457.1999489-1-joe@dama.to>
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In-Reply-To: <20260312223457.1999489-1-joe@dama.to>

On Thu, Mar 12, 2026 at 03:34:37PM -0700, Joe Damato wrote:
> Greetings:
> 
> This series extends net/tso to add a data structure and some helpers allowing
> drivers to DMA map headers and packet payloads a single time. The helpers can
> then be used to reference slices of shared mapping for each segment. This
> helps to avoid the cost of repeated DMA mappings, especially on systems which
> use an IOMMU.

In modern kernels, it is done by using DMA IOVA API, see NVMe
driver/block layer for the most comprehensive example.

The pseudo code is:
 if (with_iommu)
    use dma_iova_link/dma_iova_unlink
 else
    use dma_map_phys()

https://lore.kernel.org/all/cover.1746424934.git.leon@kernel.org/
https://lore.kernel.org/all/20250623141259.76767-1-hch@lst.de/
https://lwn.net/Articles/997563/

Thanks