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Message-ID: <2da3fb55384a222868f90562be9e1e2ca55ec1c3.camel@crapouillou.net>
Subject: Re: [PATCH v5 7/8] iio: buffer-dmaengine: Support new DMABUF based
 userspace API
From: Paul Cercueil <paul@crapouillou.net>
To: Jonathan Cameron <jic23@kernel.org>
Cc: Lars-Peter Clausen <lars@metafoo.de>, Sumit Semwal
 <sumit.semwal@linaro.org>,  Christian =?ISO-8859-1?Q?K=F6nig?=
 <christian.koenig@amd.com>, Vinod Koul <vkoul@kernel.org>, 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 18:30:40 +0100
In-Reply-To: <20231221161258.056f5ce4@jic23-huawei>
References: <20231219175009.65482-1-paul@crapouillou.net>
	 <20231219175009.65482-8-paul@crapouillou.net>
	 <20231221161258.056f5ce4@jic23-huawei>
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Hi Jonathan,

Le jeudi 21 d=C3=A9cembre 2023 =C3=A0 16:12 +0000, Jonathan Cameron a =C3=
=A9crit=C2=A0:
> On Tue, 19 Dec 2023 18:50:08 +0100
> Paul Cercueil <paul@crapouillou.net> wrote:
>=20
> > Use the functions provided by the buffer-dma core to implement the
> > DMABUF userspace API in the buffer-dmaengine IIO buffer
> > implementation.
> >=20
> > Since we want to be able to transfer an arbitrary number of bytes
> > and
> > not necesarily the full DMABUF, the associated scatterlist is
> > converted
> > to an array of DMA addresses + lengths, which is then passed to
> > dmaengine_prep_slave_dma_array().
> >=20
> > Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> One question inline. Otherwise looks fine to me.
>=20
> J
> >=20
> > ---
> > v3: Use the new dmaengine_prep_slave_dma_array(), and adapt the
> > code to
> > =C2=A0=C2=A0=C2=A0 work with the new functions introduced in industrial=
io-buffer-
> > dma.c.
> >=20
> > v5: - Use the new dmaengine_prep_slave_dma_vec().
> > =C2=A0=C2=A0=C2=A0 - Restrict to input buffers, since output buffers ar=
e not yet
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 supported by IIO buffers.
> > ---
> > =C2=A0.../buffer/industrialio-buffer-dmaengine.c=C2=A0=C2=A0=C2=A0 | 52
> > ++++++++++++++++---
> > =C2=A01 file changed, 46 insertions(+), 6 deletions(-)
> >=20
> > diff --git a/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> > b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> > index 5f85ba38e6f6..825d76a24a67 100644
> > --- a/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> > +++ b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> > @@ -64,15 +64,51 @@ static int
> > iio_dmaengine_buffer_submit_block(struct iio_dma_buffer_queue
> > *queue,
> > =C2=A0	struct dmaengine_buffer *dmaengine_buffer =3D
> > =C2=A0		iio_buffer_to_dmaengine_buffer(&queue->buffer);
> > =C2=A0	struct dma_async_tx_descriptor *desc;
> > +	unsigned int i, nents;
> > +	struct scatterlist *sgl;
> > +	struct dma_vec *vecs;
> > +	size_t max_size;
> > =C2=A0	dma_cookie_t cookie;
> > +	size_t len_total;
> > =C2=A0
> > -	block->bytes_used =3D min(block->size, dmaengine_buffer-
> > >max_size);
> > -	block->bytes_used =3D round_down(block->bytes_used,
> > -			dmaengine_buffer->align);
> > +	if (queue->buffer.direction !=3D IIO_BUFFER_DIRECTION_IN) {
> > +		/* We do not yet support output buffers. */
> > +		return -EINVAL;
> > +	}
> > =C2=A0
> > -	desc =3D dmaengine_prep_slave_single(dmaengine_buffer->chan,
> > -		block->phys_addr, block->bytes_used,
> > DMA_DEV_TO_MEM,
> > -		DMA_PREP_INTERRUPT);
> > +	if (block->sg_table) {
> > +		sgl =3D block->sg_table->sgl;
> > +		nents =3D sg_nents_for_len(sgl, block->bytes_used);
>=20
> Are we guaranteed the length in the sglist is enough?=C2=A0 If not this
> can return an error code.

The length of the sglist will always be enough, the
iio_buffer_enqueue_dmabuf() function already checks that block-
>bytes_used is equal or smaller than the size of the DMABUF.

It is quite a few functions above in the call stack though, so I can
handle the errors of sg_nents_for_len() here if you think makes sense.

Cheers,
-Paul

> > +
> > +		vecs =3D kmalloc_array(nents, sizeof(*vecs),
> > GFP_KERNEL);
> > +		if (!vecs)
> > +			return -ENOMEM;
> > +
> > +		len_total =3D block->bytes_used;
> > +
> > +		for (i =3D 0; i < nents; i++) {
> > +			vecs[i].addr =3D sg_dma_address(sgl);
> > +			vecs[i].len =3D min(sg_dma_len(sgl),
> > len_total);
> > +			len_total -=3D vecs[i].len;
> > +
> > +			sgl =3D sg_next(sgl);
> > +		}
> > +
> > +		desc =3D
> > dmaengine_prep_slave_dma_vec(dmaengine_buffer->chan,
> > +						=C2=A0=C2=A0=C2=A0 vecs, nents,
> > DMA_DEV_TO_MEM,
> > +						=C2=A0=C2=A0=C2=A0
> > DMA_PREP_INTERRUPT);
> > +		kfree(vecs);
> > +	} else {
> > +		max_size =3D min(block->size, dmaengine_buffer-
> > >max_size);
> > +		max_size =3D round_down(max_size, dmaengine_buffer-
> > >align);
> > +		block->bytes_used =3D max_size;
> > +
> > +		desc =3D
> > dmaengine_prep_slave_single(dmaengine_buffer->chan,
> > +						=C2=A0=C2=A0 block-
> > >phys_addr,
> > +						=C2=A0=C2=A0 block-
> > >bytes_used,
> > +						=C2=A0=C2=A0 DMA_DEV_TO_MEM,
> > +						=C2=A0=C2=A0
> > DMA_PREP_INTERRUPT);
> > +	}
> > =C2=A0	if (!desc)
> > =C2=A0		return -ENOMEM;
> > =C2=A0
>=20