Re: [PATCH v3 10/11] iio: buffer-dmaengine: Support new DMABUF based userspace API

[Jonathan Cameron <jic23@kernel.org>]

On Mon,  3 Apr 2023 17:49:54 +0200
Paul Cercueil <paul@crapouillou.net> 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@crapouillou.net>
A few things inline.

Thanks,

Jonathan

> 
> ---
> 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.
> ---
>  .../buffer/industrialio-buffer-dmaengine.c    | 69 ++++++++++++++++---
>  include/linux/iio/buffer-dma.h                |  2 +
>  2 files changed, 60 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/iio/buffer/industrialio-buffer-dmaengine.c b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> index 866c8b84bb24..faed9c2b089c 100644
> --- a/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> +++ b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
> @@ -65,25 +65,68 @@ static int iio_dmaengine_buffer_submit_block(struct iio_dma_buffer_queue *queue,
>  		iio_buffer_to_dmaengine_buffer(&queue->buffer);
>  	struct dma_async_tx_descriptor *desc;
>  	enum dma_transfer_direction dma_dir;
> +	unsigned int i, nents, *lenghts;
> +	struct scatterlist *sgl;
> +	unsigned long flags;
> +	dma_addr_t *addrs;
>  	size_t max_size;
>  	dma_cookie_t cookie;
> +	size_t len_total;
>  
> -	max_size = min(block->size, dmaengine_buffer->max_size);
> -	max_size = round_down(max_size, dmaengine_buffer->align);
> +	if (!block->bytes_used)
> +		return -EINVAL;
>  
> -	if (queue->buffer.direction == IIO_BUFFER_DIRECTION_IN) {
> -		block->bytes_used = max_size;
> +	if (queue->buffer.direction == IIO_BUFFER_DIRECTION_IN)
>  		dma_dir = DMA_DEV_TO_MEM;
> -	} else {
> +	else
>  		dma_dir = DMA_MEM_TO_DEV;
> -	}
>  
> -	if (!block->bytes_used || block->bytes_used > max_size)
> -		return -EINVAL;

Ah this is dropping the code I moaned about earlier.  I'll probably
forget though so maybe add a note to that patch saying it goes
away later anyway so I don't keep moaning about it in future versions.

> +	if (block->sg_table) {
> +		sgl = block->sg_table->sgl;
> +		nents = sg_nents_for_len(sgl, block->bytes_used);
> +
> +		addrs = kmalloc_array(nents, sizeof(*addrs), GFP_KERNEL);
> +		if (!addrs)
> +			return -ENOMEM;
> +
> +		lenghts = kmalloc_array(nents, sizeof(*lenghts), GFP_KERNEL);

lengths?

> +		if (!lenghts) {
> +			kfree(addrs);
> +			return -ENOMEM;
> +		}
> +
> +		len_total = block->bytes_used;
>  
> -	desc = dmaengine_prep_slave_single(dmaengine_buffer->chan,
> -		block->phys_addr, block->bytes_used, dma_dir,
> -		DMA_PREP_INTERRUPT);
> +		for (i = 0; i < nents; i++) {
> +			addrs[i] = sg_dma_address(sgl);
> +			lenghts[i] = min(sg_dma_len(sgl), len_total);
> +			len_total -= lenghts[i];
> +
> +			sgl = sg_next(sgl);
> +		}
> +
> +		flags = block->cyclic ? DMA_PREP_REPEAT : DMA_PREP_INTERRUPT;
> +
> +		desc = dmaengine_prep_slave_dma_array(dmaengine_buffer->chan,
> +						      addrs, lenghts, nents,
> +						      dma_dir, flags);
> +		kfree(addrs);
> +		kfree(lenghts);
> +	} else {
> +		max_size = min(block->size, dmaengine_buffer->max_size);
> +		max_size = round_down(max_size, dmaengine_buffer->align);
> +
> +		if (queue->buffer.direction == IIO_BUFFER_DIRECTION_IN)
> +			block->bytes_used = max_size;
> +
> +		if (block->bytes_used > max_size)
> +			return -EINVAL;
> +
> +		desc = dmaengine_prep_slave_single(dmaengine_buffer->chan,
> +						   block->phys_addr,
> +						   block->bytes_used, dma_dir,
> +						   DMA_PREP_INTERRUPT);
> +	}


> diff --git a/include/linux/iio/buffer-dma.h b/include/linux/iio/buffer-dma.h
> index e5e5817e99db..48f7ffaf0867 100644
> --- a/include/linux/iio/buffer-dma.h
> +++ b/include/linux/iio/buffer-dma.h
> @@ -43,6 +43,7 @@ enum iio_block_state {
>   * @queue: Parent DMA buffer queue
>   * @kref: kref used to manage the lifetime of block
>   * @state: Current state of the block
> + * @cyclic: True if this is a cyclic buffer
>   * @fileio: True if this buffer is used for fileio mode

I might have commented on it earlier (I've lost track) but
attach should be documented as well.   Worth sanity checking
by either building with W=1 or running kernel-doc over
the files and fixing the warnings.

>   */
>  struct iio_dma_buffer_block {
> @@ -67,6 +68,7 @@ struct iio_dma_buffer_block {
>  	 */
>  	enum iio_block_state state;
>  
> +	bool cyclic;
>  	bool fileio;
>  
>  	struct dma_buf_attachment *attach;