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

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Message-ID: <20250630133839.GA26981@lst.de>
Date: Mon, 30 Jun 2025 15:38:39 +0200
From: Christoph Hellwig <hch@....de>
To: Leon Romanovsky <leon@...nel.org>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>,
	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 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.