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Date: Fri, 5 Jul 2024 07:58:06 +0200
From: Christoph Hellwig <hch@lst.de>
To: Leon Romanovsky <leon@kernel.org>
Cc: Robin Murphy <robin.murphy@arm.com>, Jens Axboe <axboe@kernel.dk>,
	Jason Gunthorpe <jgg@ziepe.ca>, Joerg Roedel <joro@8bytes.org>,
	Will Deacon <will@kernel.org>, Keith Busch <kbusch@kernel.org>,
	Christoph Hellwig <hch@lst.de>, "Zeng, Oak" <oak.zeng@intel.com>,
	Chaitanya Kulkarni <kch@nvidia.com>,
	Sagi Grimberg <sagi@grimberg.me>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Logan Gunthorpe <logang@deltatee.com>,
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	Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>,
	Kevin Tian <kevin.tian@intel.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	=?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
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	linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org,
	kvm@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [RFC PATCH v1 18/18] nvme-pci: use new dma API
Message-ID: <20240705055806.GA11885@lst.de>
References: <cover.1719909395.git.leon@kernel.org> <47eb0510b0a6aa52d9f5665d75fa7093dd6af53f.1719909395.git.leon@kernel.org> <249ec228-4ffd-4121-bd51-f4a19275fee1@arm.com> <20240704171602.GE95824@unreal>
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User-Agent: Mutt/1.5.17 (2007-11-01)

> This is exactly how dma_map_sg() works.

Which dma_map_sg?  swiotlb handling is implemented in the underlying
ops, dma-direct and dma-iommu specifically.

dma-direct just iterates over the entries and calls dma_direct_map_page,
which does a per-entry decision to bounce based on
is_swiotlb_force_bounce, dma_capable and dma_kmalloc_needs_bounce.