[dpdk-dev] RFC: Kunpeng DMA driver API design decision

[Thomas Monjalon]

12/06/2021 09:01, fengchengwen:
> Hi all,
> 
> We prepare support Kunpeng DMA engine under rawdev framework, and observed that
> there are two different implementations of the data plane API:
> 1. rte_rawdev_enqueue/dequeue_buffers which was implemented by dpaa2_qdma and
>    octeontx2_dma driver.
> 2. rte_ioat_enqueue_xxx/rte_ioat_completed_ops which was implemented by ioat
>    driver.
> 
> Due to following consideration (mainly performance), we plan to implement API
> like ioat (not the same, have some differences) in data plane:
> 1. The rte_rawdev_enqueue_buffers use opaque buffer reference which is vendor's
>    specific, so it needs first to translate application parameters to opaque
>    pointer, and then driver writes the opaque data onto hardware, this may lead
>    to performance problem.
> 2. rte_rawdev_xxx doesn't provide memory barrier API which may need to extend
>    by opaque data (e.g. add flag to every request), this may introduce some
>    complexity.
> 
> Also the example/ioat was used to compare DMA and CPU-memcopy performance,
> Could we generalized it so that it supports multiple-vendor ?
> 
> I don't know if the community accepts this kind of implementation, so if you
> have any comments, please provide feedback.

I would love having a common generic API.
I would prefer having drivers under drivers/dma/ directory,
rather than rawdev.