linux-kernel - Re: [PATCH] dma-direct: Set SG_DMA

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Date: Mon, 6 May 2024 18:02:44 +0200
From: Christoph Hellwig <hch@....de>
To: "T.J. Mercier" <tjmercier@...gle.com>
Cc: Christoph Hellwig <hch@....de>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>, isaacmanjarres@...gle.com,
	Catalin Marinas <catalin.marinas@....com>, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma-direct: Set SG_DMA_SWIOTLB flag for dma-direct

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?