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

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Message-ID: <b32ae619-6c4a-46fc-a368-6ad4e245d581@deltatee.com>
Date: Fri, 25 Jul 2025 10:30:46 -0600
From: Logan Gunthorpe <logang@...tatee.com>
To: Leon Romanovsky <leon@...nel.org>, Christoph Hellwig <hch@....de>
Cc: Alex Williamson <alex.williamson@...hat.com>,
 Jason Gunthorpe <jgg@...dia.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 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. dma-iommu.c already uses those same interfaces and thus
there would be no need to export the low level helpers from the p2pdma code.

Logan