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Subject: Re: [PATCH v6 1/6] dmaengine: Add API function
 dmaengine_prep_slave_dma_vec()
From: Paul Cercueil <paul@crapouillou.net>
To: Vinod Koul <vkoul@kernel.org>
Cc: Jonathan Cameron <jic23@kernel.org>, Jonathan Corbet <corbet@lwn.net>, 
	Lars-Peter Clausen
	 <lars@metafoo.de>, Sumit Semwal <sumit.semwal@linaro.org>, Christian
	=?ISO-8859-1?Q?K=F6nig?=
	 <christian.koenig@amd.com>, Daniel Vetter <daniel@ffwll.ch>, Nuno Sa
	 <nuno.sa@analog.com>, Michael Hennerich <Michael.Hennerich@analog.com>, 
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, 
	dmaengine@vger.kernel.org, linux-iio@vger.kernel.org, 
	linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, 
	linaro-mm-sig@lists.linaro.org
Date: Tue, 30 Jan 2024 18:23:31 +0100
In-Reply-To: <ZbkfC31eWBUQ3kSl@matsya>
References: <20240129170201.133785-1-paul@crapouillou.net>
	 <20240129170201.133785-2-paul@crapouillou.net> <ZbkfC31eWBUQ3kSl@matsya>
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Hi Vinod,

Le mardi 30 janvier 2024 =C3=A0 21:38 +0530, Vinod Koul a =C3=A9crit=C2=A0:
> 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.
> >=20
> > 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.
> >=20
> > 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.
> >=20
> > Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> >=20
> > ---
> > v3: New patch
> >=20
> > v5: Replace with function dmaengine_prep_slave_dma_vec(), and
> > struct
> > =C2=A0=C2=A0=C2=A0 'dma_vec'.
> > =C2=A0=C2=A0=C2=A0 Note that at some point we will need to support cycl=
ic
> > transfers
> > =C2=A0=C2=A0=C2=A0 using dmaengine_prep_slave_dma_vec(). Maybe with a n=
ew "flags"
> > =C2=A0=C2=A0=C2=A0 parameter to the function?
>=20
> 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.

>=20
> > ---
> > =C2=A0include/linux/dmaengine.h | 25 +++++++++++++++++++++++++
> > =C2=A01 file changed, 25 insertions(+)
> >=20
> > 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 {
> > =C2=A0	struct data_chunk sgl[];
> > =C2=A0};
> > =C2=A0
> > +/**
> > + * 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;
> > +};
> > +
> > =C2=A0/**
> > =C2=A0 * enum dma_ctrl_flags - DMA flags to augment operation
> > preparation,
> > =C2=A0 *=C2=A0 control completion, and communicate status.
> > @@ -910,6 +920,10 @@ struct dma_device {
> > =C2=A0	struct dma_async_tx_descriptor
> > *(*device_prep_dma_interrupt)(
> > =C2=A0		struct dma_chan *chan, unsigned long flags);
> > =C2=A0
> > +	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);
>=20
> s/slave/peripheral
>=20
> I had requested it a bit while ago as well

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

Cheers,
-Paul

> > =C2=A0	struct dma_async_tx_descriptor *(*device_prep_slave_sg)(
> > =C2=A0		struct dma_chan *chan, struct scatterlist *sgl,
> > =C2=A0		unsigned int sg_len, enum dma_transfer_direction
> > direction,
> > @@ -972,6 +986,17 @@ static inline struct dma_async_tx_descriptor
> > *dmaengine_prep_slave_single(
> > =C2=A0						=C2=A0 dir, flags,
> > NULL);
> > =C2=A0}
> > =C2=A0
> > +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,
> > +						=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 dir,
> > flags);
> > +}
> > +
> > =C2=A0static inline struct dma_async_tx_descriptor
> > *dmaengine_prep_slave_sg(
> > =C2=A0	struct dma_chan *chan, struct scatterlist
> > *sgl,	unsigned int sg_len,
> > =C2=A0	enum dma_transfer_direction dir, unsigned long flags)
> > --=20
> > 2.43.0
>=20