Re: [PATCH v5 4/9] PCI/P2PDMA: Export pci_p2pdma_map_type() function

Jason Gunthorpe
2025-10-20T13:14:22Z

On Mon, Oct 20, 2025 at 05:29:06AM -0700, Christoph Hellwig wrote:
> On Fri, Oct 17, 2025 at 09:14:47AM -0300, Jason Gunthorpe wrote:
> > On Thu, Oct 16, 2025 at 11:31:53PM -0700, Christoph Hellwig wrote:
> > >
> > > Nacked-by: Christoph Hellwig <hch@lst.de>
> > >
> > > As explained to you multiple times, pci_p2pdma_map_type is a low-level
> > > helper that absolutely MUST be wrapper in proper accessors.
> >
> > You never responded to the discussion:
> >
> > https://lore.kernel.org/all/20250727190252.GF7551@nvidia.com/
> >
> > What is the plan here? Is the new DMA API unusable by modules? That
> > seems a little challenging.
>
> Yes. These are only intended to be wrapped by subsystems.

Sure, but many subsystems are fully modular too.. RDMA for example.

Well, lets see what comes in the future..

> Yes, that sounds much better. And dmabuf in general could use some
> deduplicating of their dma mapping patterns (and eventual fixing).

Yes, it certainly could, but I wanted to tackle this later..

I think adding some 'dmabuf create a map for this list of phys on this
provider' is a good simplifed primitive. Simple drivers like VFIO that
only want to expose MMIO can just call it directly.

Once this is settled I want to have RDMA wrap some of its MMIO VMAs in
DMABUF as well, so I can see at least two users of the helper.

Jason