linux-kernel - Re: [PATCH v5 3/8] dmaengine: Add API function dmaengine_prep_slave_dma

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Message-ID: <20231221114020.2d1e6364@jic23-huawei>
Date: Thu, 21 Dec 2023 11:40:20 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Paul Cercueil <paul@...pouillou.net>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Sumit Semwal
 <sumit.semwal@...aro.org>, Christian König
 <christian.koenig@....com>, Vinod Koul <vkoul@...nel.org>, Jonathan Corbet
 <corbet@....net>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 dmaengine@...r.kernel.org, linux-iio@...r.kernel.org,
 linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linaro-mm-sig@...ts.linaro.org, Nuno Sá
 <noname.nuno@...il.com>, Michael Hennerich <Michael.Hennerich@...log.com>
Subject: Re: [PATCH v5 3/8] dmaengine: Add API function
 dmaengine_prep_slave_dma_vec()

On Tue, 19 Dec 2023 18:50:04 +0100
Paul Cercueil <paul@...pouillou.net> wrote:

> This function can be used to initiate a scatter-gather DMA transfer,
> where the address and size of each segment is located in one entry of
> the dma_vec array.
> 
> The major difference with dmaengine_prep_slave_sg() is that it supports
> specifying the lengths of each DMA transfer; as trying to override the
> length of the transfer with dmaengine_prep_slave_sg() is a very tedious
> process. The introduction of a new API function is also justified by the
> fact that scatterlists are on their way out.
> 
> Note that dmaengine_prep_interleaved_dma() is not helpful either in that
> case, as it assumes that the address of each segment will be higher than
> the one of the previous segment, which we just cannot guarantee in case
> of a scatter-gather transfer.
> 
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>

This and the next patch look fine to me as clearly simplify things for
our usecases, but they are really something for the dmaengine maintainers
to comment on.

Jonathan