Re: [PATCH v3 01/11] dmaengine: Add API function dmaengine_prep_slave_dma_array()

[Hillf Danton]

On 3 Apr 2023 17:47:50 +0200 Paul Cercueil <p...@crapouillou.net>
> This function can be used to initiate a scatter-gather DMA transfer
> where the DMA addresses and lengths are located inside arrays.
> 
> The major difference with dmaengine_prep_slave_sg() is that it supports
> specifying the lengths of each DMA transfer; as trying to override the
> length of the transfer with dmaengine_prep_slave_sg() is a very tedious
> process. The introduction of a new API function is also justified by the
> fact that scatterlists are on their way out.

Given sg's wayout and conceptually iovec and kvec (in include/linux/uio.h),
what you add should have been dma_vec to ease people making use of it.

        struct dma_vec {
                dma_addr_t      addr;
                size_t          len;
        };
> 
> Signed-off-by: Paul Cercueil <p...@crapouillou.net>
> 
> ---
> v3: New patch
> ---
>  include/linux/dmaengine.h | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index c3656e590213..62efa28c009a 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -912,6 +912,11 @@ struct dma_device {
>       struct dma_async_tx_descriptor *(*device_prep_dma_interrupt)(
>               struct dma_chan *chan, unsigned long flags);
>  
> +     struct dma_async_tx_descriptor *(*device_prep_slave_dma_array)(
> +             struct dma_chan *chan, dma_addr_t *addrs,
> +             size_t *lengths, size_t nb,
> +             enum dma_transfer_direction direction,
> +             unsigned long flags);

Then the callback looks like

        struct dma_async_tx_descriptor *(*device_prep_slave_vec)(
                struct dma_chan *chan,
                struct dma_vec *vec,
                int nvec,
                enum dma_transfer_direction direction,
                unsigned long flags);