linux-kernel - Re: per-device dma_map

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Message-ID: <b491bb987c8cc3f95328d33586ec25c497cc8b8b.camel@infradead.org>
Date:   Tue, 09 Apr 2019 17:03:52 +0300
From:   David Woodhouse <dwmw2@...radead.org>
To:     Christoph Hellwig <hch@....de>, Joerg Roedel <joro@...tes.org>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: per-device dma_map_ops for intel-iommu?

On Tue, 2019-04-09 at 15:59 +0200, Christoph Hellwig wrote:
> Hi David and Joerg,
> 
> do you remember a good reason why intel-iommu is not using per-device
> dma_map_ops like the AMD iommu or the various ARM iommus?
> 
> Right now intel-iommu.c contains a half-asses reimplementation of the
> dma direct code for the iommu_no_mapping() case, and it would seem
> much nicer to just fall back to that case and not even call into
> intel-iommu in that case.

Other than the complexities about passthrough mode and various "oh shit
we forgot to actually test that iommu+gfx actually works before
shipping hardware" type of quirks that bypass the IOMMU for certain
devices — and retpolines, which I think you already dealt with — no, no
good reason that I recall.

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