Device-to-device memory-transfer offload with P2PDMA

> two functions on the same device cannot do P2P DMA with this patch series if they are plugged directly into the root port

That seems like a fairly likely use case - passing off some data from one stage of processing to another, so hopefully this restriction is lifted soon. I imagine that's a direction in the developers' sights, though - I'm happy to assume that my negligible level of domain knowledge is outdone by theirs ;-)

A couple of possible factors that might make it less of an urgent need occur to me, though, how likely are these, I wonder...?

1. How common would it be for these related functions to be plugged into the root, rather than sharing a (device internal?) bridge?

2. I imagine such devices might simply share the memory between the stages and not need DMA at all for this kind of stage-to-stage handover...?