linux-kernel - Re: [PATCH v3 01/11] dmaengine: Add API function dmaengine_prep_slave_dma

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Date:   Wed, 12 Apr 2023 22:53:26 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Nuno Sá <noname.nuno@...il.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        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
Subject: Re: [PATCH v3 01/11] dmaengine: Add API function
 dmaengine_prep_slave_dma_array()

On 03-04-23, 17:47, Paul Cercueil wrote:
> This function can be used to initiate a scatter-gather DMA transfer
> where the DMA addresses and lengths are located inside arrays.
> 
> 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.

Do we need a new API for this? why not use device_prep_interleaved_dma?

> 
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> 
> ---
> v3: New patch
> ---
>  include/linux/dmaengine.h | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index c3656e590213..62efa28c009a 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -912,6 +912,11 @@ struct dma_device {
>  	struct dma_async_tx_descriptor *(*device_prep_dma_interrupt)(
>  		struct dma_chan *chan, unsigned long flags);
>  
> +	struct dma_async_tx_descriptor *(*device_prep_slave_dma_array)(
> +		struct dma_chan *chan, dma_addr_t *addrs,
> +		size_t *lengths, size_t nb,
> +		enum dma_transfer_direction direction,
> +		unsigned long flags);
>  	struct dma_async_tx_descriptor *(*device_prep_slave_sg)(
>  		struct dma_chan *chan, struct scatterlist *sgl,
>  		unsigned int sg_len, enum dma_transfer_direction direction,
> @@ -974,6 +979,17 @@ static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_single(
>  						  dir, flags, NULL);
>  }
>  
> +static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_dma_array(
> +	struct dma_chan *chan, dma_addr_t *addrs, size_t *lengths,
> +	size_t nb, enum dma_transfer_direction dir, unsigned long flags)
> +{
> +	if (!chan || !chan->device || !chan->device->device_prep_slave_dma_array)
> +		return NULL;
> +
> +	return chan->device->device_prep_slave_dma_array(chan, addrs, lengths,
> +							 nb, dir, flags);
> +}
> +
>  static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_sg(
>  	struct dma_chan *chan, struct scatterlist *sgl,	unsigned int sg_len,
>  	enum dma_transfer_direction dir, unsigned long flags)
> -- 
> 2.39.2

-- 
~Vinod