linux-kernel - Re: [PATCH 0/8] dma-mapping: migrate to physical address-based API

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Message-ID: <20250708110007.GF592765@unreal>
Date: Tue, 8 Jul 2025 14:00:07 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Christoph Hellwig <hch@....de>, Jonathan Corbet <corbet@....net>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Alexander Potapenko <glider@...gle.com>,
	Marco Elver <elver@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Jérôme Glisse <jglisse@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, iommu@...ts.linux.dev,
	virtualization@...ts.linux.dev, kasan-dev@...glegroups.com,
	linux-trace-kernel@...r.kernel.org, linux-mm@...ck.org,
	Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH 0/8] dma-mapping: migrate to physical address-based API

On Tue, Jul 08, 2025 at 12:27:09PM +0200, Marek Szyprowski wrote:
> On 30.06.2025 15:38, Christoph Hellwig wrote:
> > On Fri, Jun 27, 2025 at 08:02:13PM +0300, Leon Romanovsky wrote:
> >>> Thanks for this rework! I assume that the next step is to add map_phys
> >>> callback also to the dma_map_ops and teach various dma-mapping providers
> >>> to use it to avoid more phys-to-page-to-phys conversions.
> >> Probably Christoph will say yes, however I personally don't see any
> >> benefit in this. Maybe I wrong here, but all existing .map_page()
> >> implementation platforms don't support p2p anyway. They won't benefit
> >> from this such conversion.
> > I think that conversion should eventually happen, and rather sooner than
> > later.
> 
> Agreed.
> 
> Applied patches 1-7 to my dma-mapping-next branch. Let me know if one 
> needs a stable branch with it.

Thanks a lot, I don't think that stable branch is needed. Realistically
speaking, my VFIO DMA work won't be merged this cycle, We are in -rc5,
it is complete rewrite from RFC version and touches pci-p2p code (to
remove dependency on struct page) in addition to VFIO, so it will take
time.

Regarding, last patch (hmm), it will be great if you can take it.
We didn't touch anything in hmm.c this cycle and have no plans to send PR.
It can safely go through your tree.

> 
> Leon, it would be great if You could also prepare an incremental patch 
> adding map_phys callback to the dma_maps_ops, so the individual 
> arch-specific dma-mapping providers can be then converted (or simplified 
> in many cases) too.

Sure, will do.

> 
> Best regards
> -- 
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
>