Re: [PATCH v4 1/5] PCI/P2PDMA: Don't enforce ACS check for device functions of Intel GPUs

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Sep 25, 2025 at 05:40:25PM +0200, Thomas Hellström wrote:
> > I think is also needs an API that is not based on scatterlist. Please
> > lets not push a private interconnect address through the scatterlist
> > dma_addr_t!
> 
> I think that needs to be defined per interconnect, choosing a data
> structure that suits best. Although I find it reasonable to mandate
> dma_addr_t or scatterlists to *not* be used.

Can you include some sketch of how that would look? And cc me please
on future versions :)

> > Assuming that you imagine we'd define some global well known
> > interconnect
> > 
> > 'struct blah pci_bar_interconnect {..}'
> > 
> > And if that is negotiated then the non-scatterlist communication
> > would
> > give the (struct pci_dev *, bar index, bar offset) list?
> 
> Yes something like that. Although I think perhaps the dev + bar index
> might be part of the negotiation, so that it is rejected if the
> importer feels that there is no implied PF + VF interconnect. Then the
> list would be reduced to only the offset.

I'm also happy if the list is just a list of bar offsets for a single
bar and the pci_dev/bar index is discovered by the importer before
getting the list.

That's probably a better API design anyhow since building the list
just to check the pci_dev is wasteful.

In this case a simple vmap of bar offset / len pairs would be nice and
easy place to start.

Jason