On Thu, 2023-12-21 at 18:30 +0100, Paul Cercueil wrote:
> Hi Jonathan,
>
> Le jeudi 21 décembre 2023 à 16:12 +0000, Jonathan Cameron a écrit :
> > On Tue, 19 Dec 2023 18:50:08 +0100
> > Paul Cercueil <paul@xxxxxxxxxxxxxxx> wrote:
> >
> > > Use the functions provided by the buffer-dma core to implement the
> > > DMABUF userspace API in the buffer-dmaengine IIO buffer
> > > implementation.
> > >
> > > 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().
> > >
> > > Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> > One question inline. Otherwise looks fine to me.
> >
> > J
> > >
> > > ---
> > > v3: Use the new dmaengine_prep_slave_dma_array(), and adapt the
> > > code to
> > > work with the new functions introduced in industrialio-buffer-
> > > dma.c.
> > >
> > > v5: - Use the new dmaengine_prep_slave_dma_vec().
> > > - Restrict to input buffers, since output buffers are not yet
> > > supported by IIO buffers.
> > > ---
> > > .../buffer/industrialio-buffer-dmaengine.c | 52
> > > ++++++++++++++++---
> > > 1 file changed, 46 insertions(+), 6 deletions(-)
> > >
> > > 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,
> > > struct dmaengine_buffer *dmaengine_buffer =
> > > iio_buffer_to_dmaengine_buffer(&queue->buffer);
> > > struct dma_async_tx_descriptor *desc;
> > > + unsigned int i, nents;
> > > + struct scatterlist *sgl;
> > > + struct dma_vec *vecs;
> > > + size_t max_size;
> > > dma_cookie_t cookie;
> > > + size_t len_total;
> > >
> > > - block->bytes_used = min(block->size, dmaengine_buffer-
> > > > max_size);
> > > - block->bytes_used = round_down(block->bytes_used,
> > > - dmaengine_buffer->align);
> > > + if (queue->buffer.direction != IIO_BUFFER_DIRECTION_IN) {
> > > + /* We do not yet support output buffers. */
> > > + return -EINVAL;
> > > + }
> > >
> > > - desc = 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 = block->sg_table->sgl;
> > > + nents = sg_nents_for_len(sgl, block->bytes_used);
> >
> > Are we guaranteed the length in the sglist is enough? 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.
Maybe putting something like the above in a comment?
- Nuno Sá
