linux-kernel - Re: [PATCH] iommu/dma: Respect SWIOTLB force

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Date: Wed, 1 May 2024 22:07:35 -0700
From: Christoph Hellwig <hch@...radead.org>
To: "T.J. Mercier" <tjmercier@...gle.com>
Cc: Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Catalin Marinas <catalin.marinas@....com>,
	isaacmanjarres@...gle.com, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/dma: Respect SWIOTLB force_bounce

On Wed, May 01, 2024 at 08:13:18PM +0000, T.J. Mercier wrote:
> iommu_dma_map_page and iommu_dma_map_sg conditionally use SWIOTLB, but
> checking if force_bounce is set for the device is not part of that
> condition. Check if devices have requested to force SWIOTLB use as part
> of deciding to take the existing SWIOTLB paths.

This fails to explain why you'd want this somewhat surprising behavior,
and why you consider it a bug fix.