Re: [PATCH v3 6/6] iio: buffer-dma: add support for cyclic DMA transfers

[Alexandru Ardelean <ardeleanalex@gmail.com>]

On Sun, Feb 21, 2021 at 2:11 PM Jonathan Cameron <jic23@kernel.org> wrote:
>
> On Fri, 19 Feb 2021 14:40:12 +0200
> Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:
>
> > From: Lars-Peter Clausen <lars@metafoo.de>
> >
> > This change adds support for cyclic DMA transfers using the IIO buffer DMA
> > infrastructure.
> > To do this, userspace must set the IIO_BUFFER_BLOCK_FLAG_CYCLIC flag on the
> > block when enqueueing them via the ENQUEUE_BLOCK ioctl().
> >
> > Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
> > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> Series in general looks good to me, but this change needs a little more
> detail + probably some level of example userspace flow.
>
> I don't really understand how this is used!
>
> Also, it's easy to test output buffers with the kfifo support so we
> should be able to move forward quickly with that part (1-3, 4 is probably
> fine as well as clearly harmless).
>
> The dma stuff worries me more, at least partly based on the experience
> of the original dma buffers which basically sat their unused (in upstream)
> for a very long time.   So to move these forward, they need to come
> with users...

So, this series will need to be re-sent/re-tested by someone else.
I'm on my last week at ADI and I'm on vacation.

Maybe I can manage to setup something to test as well, but it will take a while.



>
> Thanks,
>
> Jonathan
>
> > ---
> >  .../buffer/industrialio-buffer-dmaengine.c    | 24 ++++++++++++-------
> >  include/uapi/linux/iio/buffer.h               |  1 +
> >  2 files changed, 17 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/iio/buffer/industrialio-buffer-dmaengine.c b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> > index 65458a6cc81a..39cc230c7991 100644
> > --- a/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> > +++ b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> > @@ -82,14 +82,22 @@ static int iio_dmaengine_buffer_submit_block(struct iio_dma_buffer_queue *queue,
> >
> >       direction = dmaengine_buffer->is_tx ? DMA_MEM_TO_DEV : DMA_DEV_TO_MEM;
> >
> > -     desc = dmaengine_prep_slave_single(dmaengine_buffer->chan,
> > -             block->phys_addr, block->block.bytes_used, direction,
> > -             DMA_PREP_INTERRUPT);
> > -     if (!desc)
> > -             return -ENOMEM;
> > -
> > -     desc->callback_result = iio_dmaengine_buffer_block_done;
> > -     desc->callback_param = block;
> > +     if (block->block.flags & IIO_BUFFER_BLOCK_FLAG_CYCLIC) {
> > +             desc = dmaengine_prep_dma_cyclic(dmaengine_buffer->chan,
> > +                     block->phys_addr, block->block.bytes_used,
> > +                     block->block.bytes_used, direction, 0);
> > +             if (!desc)
> > +                     return -ENOMEM;
> > +     } else {
> > +             desc = dmaengine_prep_slave_single(dmaengine_buffer->chan,
> > +                     block->phys_addr, block->block.bytes_used, direction,
> > +                     DMA_PREP_INTERRUPT);
> > +             if (!desc)
> > +                     return -ENOMEM;
> > +
> > +             desc->callback_result = iio_dmaengine_buffer_block_done;
> > +             desc->callback_param = block;
> > +     }
> >
> >       cookie = dmaengine_submit(desc);
> >       if (dma_submit_error(cookie))
> > diff --git a/include/uapi/linux/iio/buffer.h b/include/uapi/linux/iio/buffer.h
> > index 4e4ee9befea1..1bde508fe1b9 100644
> > --- a/include/uapi/linux/iio/buffer.h
> > +++ b/include/uapi/linux/iio/buffer.h
> > @@ -33,6 +33,7 @@ struct iio_buffer_block_alloc_req {
> >
> >  /* A function will be assigned later for BIT(0) */
> >  #define IIO_BUFFER_BLOCK_FLAG_RESERVED               (1 << 0)
> > +#define IIO_BUFFER_BLOCK_FLAG_CYCLIC         (1 << 1)
> >
> >  /**
> >   * struct iio_buffer_block - Descriptor for a single IIO block
>