Re: [PATCH v1 00/17] Provide a new two step DMA mapping API

[Christoph Hellwig]

On Fri, Nov 08, 2024 at 11:25:37AM -0400, Jason Gunthorpe wrote:
> I'm asking how it will work if you change the struct page argument to
> physical, because today dma_direct_map_page() has:
> 
> 		if (is_pci_p2pdma_page(page))
> 			return DMA_MAPPING_ERROR;
> 
> Which is exactly the sorts of things I'm looking at when when I say to
> get rid of struct page.

It will have to look up the page from the physical address obviously.
But at least only in the error path.

> What I'm thinking about is replacing code like the above with something like:
> 
> 		if (p2p_provider)
> 			return DMA_MAPPING_ERROR;
> 
> And the caller is the one that would have done is_pci_p2pdma_page()
> and either passes p2p_provider=NULL or page->pgmap->p2p_provider.

And where do you get that one from?