linux-kernel - Re: [PATCH v6 1/6] dmaengine: Add API function dmaengine_prep_slave_dma

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Message-ID: <ZbkfC31eWBUQ3kSl@matsya>
Date: Tue, 30 Jan 2024 21:38:43 +0530
From: Vinod Koul <vkoul@...nel.org>
To: Paul Cercueil <paul@...pouillou.net>
Cc: Jonathan Cameron <jic23@...nel.org>, Jonathan Corbet <corbet@....net>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	Daniel Vetter <daniel@...ll.ch>, Nuno Sa <nuno.sa@...log.com>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	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
Subject: Re: [PATCH v6 1/6] dmaengine: Add API function
 dmaengine_prep_slave_dma_vec()

On 29-01-24, 18:01, Paul Cercueil 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>
> 
> ---
> v3: New patch
> 
> v5: Replace with function dmaengine_prep_slave_dma_vec(), and struct
>     'dma_vec'.
>     Note that at some point we will need to support cyclic transfers
>     using dmaengine_prep_slave_dma_vec(). Maybe with a new "flags"
>     parameter to the function?

that would be better

> ---
>  include/linux/dmaengine.h | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 3df70d6131c8..ee5931ddb42f 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -160,6 +160,16 @@ struct dma_interleaved_template {
>  	struct data_chunk sgl[];
>  };
>  
> +/**
> + * struct dma_vec - DMA vector
> + * @addr: Bus address of the start of the vector
> + * @len: Length in bytes of the DMA vector
> + */
> +struct dma_vec {
> +	dma_addr_t addr;
> +	size_t len;
> +};
> +
>  /**
>   * enum dma_ctrl_flags - DMA flags to augment operation preparation,
>   *  control completion, and communicate status.
> @@ -910,6 +920,10 @@ 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_vec)(
> +		struct dma_chan *chan, const struct dma_vec *vecs,
> +		size_t nents, enum dma_transfer_direction direction,
> +		unsigned long flags);

s/slave/peripheral

I had requested it a bit while ago as well

>  	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,
> @@ -972,6 +986,17 @@ 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_vec(
> +	struct dma_chan *chan, const struct dma_vec *vecs, size_t nents,
> +	enum dma_transfer_direction dir, unsigned long flags)
> +{
> +	if (!chan || !chan->device || !chan->device->device_prep_slave_dma_vec)
> +		return NULL;
> +
> +	return chan->device->device_prep_slave_dma_vec(chan, vecs, nents,
> +						       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)
> -- 
> 2.43.0

-- 
~Vinod