Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory

[Benjamin Herrenschmidt <benh-XVmvHMARGAS8U2dJNN8I7kB+6BGkLq7r@public.gmane.org>]

On Tue, 2017-04-18 at 10:27 -0700, Dan Williams wrote:
> > FWIW, RDMA probably wouldn't want to use a p2mem device either, we
> > already have APIs that map BAR memory to user space, and would like to
> > keep using them. A 'enable P2P for bar' helper function sounds better
> > to me.
> 
> ...and I think it's not a helper function as much as asking the bus
> provider "can these two device dma to each other". The "helper" is the
> dma api redirecting through a software-iommu that handles bus address
> translation differently than it would handle host memory dma mapping.

Do we even need tat function ? The dma_ops have a dma_supported()
call...

If we have those override ops built into the "dma_target" object,
then these things can make that decision knowing both the source
and target device.

Cheers,
Ben.