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

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Message-ID: <69b177dc-c149-40d3-bbde-3f6bad0efd0e@samsung.com>
Date: Tue, 8 Jul 2025 12:27:09 +0200
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Christoph Hellwig <hch@....de>, Leon Romanovsky <leon@...nel.org>
Cc: 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 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.

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.

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