Re: [RFC PATCH 5/5] iio: buffer-dma: add support for cyclic DMA transfers

[Jonathan Cameron]

On Fri, 12 Feb 2021 12:20:21 +0200
Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx> wrote:

> From: Lars-Peter Clausen <lars@xxxxxxxxxx>
> 
> 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().

We should have more than that in the way of documentation!

What is the dataflow that we end up with as a result of this?

Jonathan


> 
> Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
> ---
>  .../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 013cc7c1ecf4..94c93a636ad4 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 70ad3aea01ea..0e0c95f1c38b 100644
> --- a/include/uapi/linux/iio/buffer.h
> +++ b/include/uapi/linux/iio/buffer.h
> @@ -13,6 +13,7 @@ struct iio_buffer_block_alloc_req {
>  };
>  
>  #define IIO_BUFFER_BLOCK_FLAG_TIMESTAMP_VALID	(1 << 0)
> +#define IIO_BUFFER_BLOCK_FLAG_CYCLIC		(1 << 1)
>  
>  struct iio_buffer_block {
>  	__u32 id;