Re: [PATCH 06/12] IB/core: Add optional PCI P2P flag to rdma_rw_ctx_[init|destroy]()

[Logan Gunthorpe]

On 08/01/18 11:09 AM, Jason Gunthorpe wrote:
> It could, if we had a DMA op for p2p then the drivers that provide
> their own ops can implement it appropriately or not at all.

I was thinking of doing something like this. I'll probably rough out a 
patch and send it along today or tomorrow.

> > If at all it should be in the dma_map* wrappers, but for that we'd need
> > a good identifier.  And it still would not solve the whole fake dma
> > ops issue.
>
> Very long term the IOMMUs under the ops will need to care about this,
> so the wrapper is not an optimal place to put it - but I wouldn't
> object if it gets it out of RDMA :)

Well, creating the extra op doesn't really change anything to the RDMA 
patch in this series. The point is, for the time being, we need to track 
whether we are doing a P2P or normal mapping using a side channel as we 
don't have a good way of tracking it in the SGL at this time.

Adding an extra DMA op is just one way to allow the existing DMA 
providers to opt-in/out.

Logan