linux-kernel - Re: [PATCH 05/10] PCI/P2PDMA: Export pci_p2pdma_map

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Message-ID: <20250727190514.GG7551@nvidia.com>
Date: Sun, 27 Jul 2025 16:05:14 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Logan Gunthorpe <logang@...tatee.com>
Cc: Leon Romanovsky <leon@...nel.org>, Christoph Hellwig <hch@....de>,
	Alex Williamson <alex.williamson@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Christian König <christian.koenig@....com>,
	dri-devel@...ts.freedesktop.org, iommu@...ts.linux.dev,
	Jens Axboe <axboe@...nel.dk>,
	Jérôme Glisse <jglisse@...hat.com>,
	Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
	linaro-mm-sig@...ts.linaro.org, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	linux-mm@...ck.org, linux-pci@...r.kernel.org,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Vivek Kasireddy <vivek.kasireddy@...el.com>,
	Will Deacon <will@...nel.org>
Subject: Re: [PATCH 05/10] PCI/P2PDMA: Export pci_p2pdma_map_type() function

On Fri, Jul 25, 2025 at 10:30:46AM -0600, Logan Gunthorpe wrote:
> 
> 
> On 2025-07-24 02:13, Leon Romanovsky wrote:
> > On Thu, Jul 24, 2025 at 10:03:13AM +0200, Christoph Hellwig wrote:
> >> On Wed, Jul 23, 2025 at 04:00:06PM +0300, Leon Romanovsky wrote:
> >>> From: Leon Romanovsky <leonro@...dia.com>
> >>>
> >>> Export the pci_p2pdma_map_type() function to allow external modules
> >>> and subsystems to determine the appropriate mapping type for P2PDMA
> >>> transfers between a provider and target device.
> >>
> >> External modules have no business doing this.
> > 
> > VFIO PCI code is built as module. There is no way to access PCI p2p code
> > without exporting functions in it.
> 
> The solution that would make more sense to me would be for either
> dma_iova_try_alloc() or another helper in dma-iommu.c to handle the
> P2PDMA case.

This has nothing to do with dma-iommu.c, the decisions here still need
to be made even if dma-iommu.c is not compiled in.

It could be exported from the main dma code, but I think it would just
be a 1 line wrapper around the existing function? I'd rather rename
the functions and leave them in the p2pdma.c files...

Jason