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Date: Mon, 6 May 2024 18:02:44 +0200
From: Christoph Hellwig <hch@lst.de>
To: "T.J. Mercier" <tjmercier@google.com>
Cc: Christoph Hellwig <hch@lst.de>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Robin Murphy <robin.murphy@arm.com>, isaacmanjarres@google.com,
	Catalin Marinas <catalin.marinas@arm.com>, iommu@lists.linux.dev,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] dma-direct: Set SG_DMA_SWIOTLB flag for dma-direct
Message-ID: <20240506160244.GA16248@lst.de>
References: <20240503183713.1557480-1-tjmercier@google.com> <20240506052955.GA4923@lst.de> <CABdmKX1XNTtoPTvfsJRobim8pHdDjPsKx=qVovVZDh5GEbKCfQ@mail.gmail.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Mon, May 06, 2024 at 09:00:59AM -0700, T.J. Mercier wrote:
> Oh, that's disappointing. I'm looking for a way to quickly check if
> any addresses point at a SWIOTLB buffer without doing a potentially
> expensive call to iommu_iova_to_phys. Since it's meant to be dma-iommu
> only I guess I could use sg_dma_is_swiotlb if iommu_get_domain_for_dev
> returns a domain, and is_swiotlb_buffer otherwise for dma-direct, but
> it'd be nice to have just one way to check which it looked like the
> SG_DMA_SWIOTLB flag could be used for.

This sounds like you're trying to do that from a consumer of the
DMA API, which is simply wrong.  What is the actual problem you are
trying to solve?