Received-SPF: pass (google.com: domain of linux-kernel+bounces-8663-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Message-ID: <fdfa480e2e702e4e0e96269ac579f2ee750f1fc1.camel@crapouillou.net>
Subject: Re: [PATCH v5 3/8] 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>, Lars-Peter Clausen
 <lars@metafoo.de>,  Sumit Semwal <sumit.semwal@linaro.org>, Christian
 =?ISO-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,  Jonathan Corbet
 <corbet@lwn.net>, 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, Nuno =?ISO-8859-1?Q?S=E1?=
 <noname.nuno@gmail.com>, Michael Hennerich <Michael.Hennerich@analog.com>
Date: Thu, 21 Dec 2023 16:29:27 +0100
In-Reply-To: <ZYRWbROAuMXftH07@matsya>
References: <20231219175009.65482-1-paul@crapouillou.net>
	 <20231219175009.65482-4-paul@crapouillou.net> <ZYRWbROAuMXftH07@matsya>
Autocrypt: addr=paul@crapouillou.net; prefer-encrypt=mutual;
 keydata=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
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk
MIME-Version: 1.0

Hi Vinod,

Le jeudi 21 d=C3=A9cembre 2023 =C3=A0 20:44 +0530, Vinod Koul a =C3=A9crit=
=C2=A0:
> On 19-12-23, 18:50, 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?
> > ---
> > =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;
> > +};
>=20
> so you want to transfer multiple buffers, right? why not use
> dmaengine_prep_slave_sg(). If there is reason for not using that one?

Well I think I answer that in the commit message, don't I?

> Furthermore I missed replying to your email earlier on use of
> dmaengine_prep_interleaved_dma(), my apologies.
> That can be made to work for you as well. Please see the notes where
> icg
> can be ignored and it does not need icg value to be set
>=20
> Infact, interleaved api can be made to work in most of these cases I
> can
> think of...

So if I want to transfer 16 bytes from 0x10, then 16 bytes from 0x0,
then 16 bytes from 0x20, how should I configure the
dma_interleaved_template?

Cheers,
-Paul

> > +
> > =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);
> > =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