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Date: Mon, 30 Jun 2025 15:38:39 +0200
From: Christoph Hellwig <hch@lst.de>
To: Leon Romanovsky <leon@kernel.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>,
	Christoph Hellwig <hch@lst.de>, Jonathan Corbet <corbet@lwn.net>,
	Madhavan Srinivasan <maddy@linux.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Nicholas Piggin <npiggin@gmail.com>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	Robin Murphy <robin.murphy@arm.com>, Joerg Roedel <joro@8bytes.org>,
	Will Deacon <will@kernel.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Jason Wang <jasowang@redhat.com>,
	Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
	Eugenio =?iso-8859-1?Q?P=E9rez?= <eperezma@redhat.com>,
	Alexander Potapenko <glider@google.com>,
	Marco Elver <elver@google.com>, Dmitry Vyukov <dvyukov@google.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	=?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, iommu@lists.linux.dev,
	virtualization@lists.linux.dev, kasan-dev@googlegroups.com,
	linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org,
	Jason Gunthorpe <jgg@ziepe.ca>
Subject: Re: [PATCH 0/8] dma-mapping: migrate to physical address-based API
Message-ID: <20250630133839.GA26981@lst.de>
References: <CGME20250625131920eucas1p271b196cde042bd39ac08fb12beff5baf@eucas1p2.samsung.com> <cover.1750854543.git.leon@kernel.org> <35df6f2a-0010-41fe-b490-f52693fe4778@samsung.com> <20250627170213.GL17401@unreal>
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User-Agent: Mutt/1.5.17 (2007-11-01)

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.