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

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Message-ID: <35df6f2a-0010-41fe-b490-f52693fe4778@samsung.com>
Date: Fri, 27 Jun 2025 15:44:10 +0200
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Leon Romanovsky <leon@...nel.org>
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 25.06.2025 15:18, Leon Romanovsky wrote:
> This series refactors the DMA mapping to use physical addresses
> as the primary interface instead of page+offset parameters. This
> change aligns the DMA API with the underlying hardware reality where
> DMA operations work with physical addresses, not page structures.
>
> The series consists of 8 patches that progressively convert the DMA
> mapping infrastructure from page-based to physical address-based APIs:
>
> The series maintains backward compatibility by keeping the old
> page-based API as wrapper functions around the new physical
> address-based implementations.

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.

I only wonder if this newly introduced dma_map_phys()/dma_unmap_phys() 
API is also suitable for the recently discussed PCI P2P DMA? While 
adding a new API maybe we should take this into account? My main concern 
is the lack of the source phys addr passed to the dma_unmap_phys() 
function and I'm aware that this might complicate a bit code conversion 
from old dma_map/unmap_page() API.

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