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From: Leon Romanovsky <leon@kernel.org>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: "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 Pérez" <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>,
	"Jérôme 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
Date: Fri, 27 Jun 2025 20:02:13 +0300	[thread overview]
Message-ID: <20250627170213.GL17401@unreal> (raw)
In-Reply-To: <35df6f2a-0010-41fe-b490-f52693fe4778@samsung.com>

On Fri, Jun 27, 2025 at 03:44:10PM +0200, Marek Szyprowski wrote:
> 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.

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 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?

First, immediate user (not related to p2p) is blk layer:
https://lore.kernel.org/linux-nvme/bcdcb5eb-17ed-412f-bf5c-303079798fe2@nvidia.com/T/#m7e715697d4b2e3997622a3400243477c75cab406

+static bool blk_dma_map_direct(struct request *req, struct device *dma_dev,
+		struct blk_dma_iter *iter, struct phys_vec *vec)
+{
+	iter->addr = dma_map_page(dma_dev, phys_to_page(vec->paddr),
+			offset_in_page(vec->paddr), vec->len, rq_dma_dir(req));
+	if (dma_mapping_error(dma_dev, iter->addr)) {
+		iter->status = BLK_STS_RESOURCE;
+		return false;
+	}
+	iter->len = vec->len;
+	return true;
+}

Block layer started to store phys addresses instead of struct pages and
this phys_to_page() conversion in data-path will be avoided.

> 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
> 
> 

  reply	other threads:[~2025-06-27 17:02 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20250625131920eucas1p271b196cde042bd39ac08fb12beff5baf@eucas1p2.samsung.com>
2025-06-25 13:18 ` [PATCH 0/8] dma-mapping: migrate to physical address-based API Leon Romanovsky
2025-06-25 13:18   ` [PATCH 1/8] dma-debug: refactor to use physical addresses for page mapping Leon Romanovsky
2025-06-25 13:18   ` [PATCH 2/8] dma-mapping: rename trace_dma_*map_page to trace_dma_*map_phys Leon Romanovsky
2025-06-25 13:19   ` [PATCH 3/8] iommu/dma: rename iommu_dma_*map_page to iommu_dma_*map_phys Leon Romanovsky
2025-06-25 13:19   ` [PATCH 4/8] dma-mapping: convert dma_direct_*map_page to be phys_addr_t based Leon Romanovsky
2025-06-25 13:19   ` [PATCH 5/8] kmsan: convert kmsan_handle_dma to use physical addresses Leon Romanovsky
2025-06-26 17:43     ` Alexander Potapenko
2025-06-26 18:45       ` Leon Romanovsky
2025-06-27 16:28         ` Alexander Potapenko
2025-06-25 13:19   ` [PATCH 6/8] dma-mapping: fail early if physical address is mapped through platform callback Leon Romanovsky
2025-07-25 20:04     ` Robin Murphy
2025-07-27  6:30       ` Leon Romanovsky
2025-06-25 13:19   ` [PATCH 7/8] dma-mapping: export new dma_*map_phys() interface Leon Romanovsky
2025-06-25 13:19   ` [PATCH 8/8] mm/hmm: migrate to physical address-based DMA mapping API Leon Romanovsky
2025-07-15 13:24     ` Will Deacon
2025-07-15 13:58       ` Leon Romanovsky
2025-06-27 13:44   ` [PATCH 0/8] dma-mapping: migrate to physical address-based API Marek Szyprowski
2025-06-27 17:02     ` Leon Romanovsky [this message]
2025-06-30 13:38       ` Christoph Hellwig
2025-07-08 10:27         ` Marek Szyprowski
2025-07-08 11:00           ` Leon Romanovsky
2025-07-08 11:45             ` Marek Szyprowski
2025-07-08 12:06               ` Leon Romanovsky
2025-07-08 12:56                 ` Marek Szyprowski
2025-07-08 15:57                   ` Marek Szyprowski
2025-07-30 11:11           ` Robin Murphy
2025-07-30 13:40             ` Leon Romanovsky
2025-07-30 14:28               ` Jason Gunthorpe
2025-07-31  6:01                 ` Leon Romanovsky
2025-07-30 16:32             ` Marek Szyprowski
2025-07-31 17:37             ` Matthew Wilcox
2025-08-03 15:59               ` Jason Gunthorpe
2025-08-04  3:37                 ` Matthew Wilcox
2025-08-05 15:36                   ` Jason Gunthorpe
2025-07-06  6:00       ` Leon Romanovsky
2025-07-25 20:05   ` Robin Murphy
2025-07-29 14:03     ` Jason Gunthorpe

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