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

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Message-ID: <fcf3e49cae178b18c0b15e12c69f9f2a84e8312e.camel@crapouillou.net>
Date: Tue, 30 Jan 2024 18:23:31 +0100
From: Paul Cercueil <paul@...pouillou.net>
To: Vinod Koul <vkoul@...nel.org>
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()

Hi Vinod,

Le mardi 30 janvier 2024 à 21:38 +0530, Vinod Koul a écrit :
> 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

Ok, I think it'd be better that I add a new "flags" parameter now -
even if it means passing 0 until we actually have flags for it.

> 
> > ---
> >  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

You did. Sorry, I forgot about it when working on the v6.

Cheers,
-Paul

> >  	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
>