On 29-01-24, 18:01, Paul Cercueil wrote:
> This function can be used to initiate a scatter-gather DMA transfer,
> where the address and size of each segment is located in one entry of
> the dma_vec array.
>
> 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.
>
> Note that dmaengine_prep_interleaved_dma() is not helpful either in that
> case, as it assumes that the address of each segment will be higher than
> the one of the previous segment, which we just cannot guarantee in case
> of a scatter-gather transfer.
>
> Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
>
> ---
> v3: New patch
>
> v5: Replace with function dmaengine_prep_slave_dma_vec(), and struct
> 'dma_vec'.
> Note that at some point we will need to support cyclic transfers
> using dmaengine_prep_slave_dma_vec(). Maybe with a new "flags"
> parameter to the function?
that would be better
> ---
> include/linux/dmaengine.h | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 3df70d6131c8..ee5931ddb42f 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -160,6 +160,16 @@ struct dma_interleaved_template {
> struct data_chunk sgl[];
> };
>
> +/**
> + * struct dma_vec - DMA vector
> + * @addr: Bus address of the start of the vector
> + * @len: Length in bytes of the DMA vector
> + */
> +struct dma_vec {
> + dma_addr_t addr;
> + size_t len;
> +};
> +
> /**
> * enum dma_ctrl_flags - DMA flags to augment operation preparation,
> * control completion, and communicate status.
> @@ -910,6 +920,10 @@ 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_vec)(
> + struct dma_chan *chan, const struct dma_vec *vecs,
> + size_t nents, enum dma_transfer_direction direction,
> + unsigned long flags);
s/slave/peripheral
I had requested it a bit while ago as well
> struct dma_async_tx_descriptor *(*device_prep_slave_sg)(
> struct dma_chan *chan, struct scatterlist *sgl,
> unsigned int sg_len, enum dma_transfer_direction direction,
> @@ -972,6 +986,17 @@ static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_single(
> dir, flags, NULL);
> }
>
> +static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_dma_vec(
> + struct dma_chan *chan, const struct dma_vec *vecs, size_t nents,
> + enum dma_transfer_direction dir, unsigned long flags)
> +{
> + if (!chan || !chan->device || !chan->device->device_prep_slave_dma_vec)
> + return NULL;
> +
> + return chan->device->device_prep_slave_dma_vec(chan, vecs, nents,
> + dir, flags);
> +}
> +
> static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_sg(
> struct dma_chan *chan, struct scatterlist *sgl, unsigned int sg_len,
> enum dma_transfer_direction dir, unsigned long flags)
> --
> 2.43.0
--
~Vinod
