linux-kernel - Re: [PATCH 2/2] dma: Add IOMMU static calls with clear default ops

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Message-ID: <20240713051813.GA25733@lst.de>
Date: Sat, 13 Jul 2024 07:18:13 +0200
From: Christoph Hellwig <hch@....de>
To: Robin Murphy <robin.murphy@....com>
Cc: Leon Romanovsky <leon@...nel.org>, Christoph Hellwig <hch@....de>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Jason Gunthorpe <jgg@...dia.com>, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev
Subject: Re: [PATCH 2/2] dma: Add IOMMU static calls with clear default ops

On Fri, Jul 12, 2024 at 03:21:55PM +0100, Robin Murphy wrote:
>> This is done to keep layering similar to existing in DMA subsystem. We
>> have special files and calls to dma-direct, it looks natural to have
>> special files and call to dma-iommu. It is not nice to call to drivers/iommu
>> from kernel/dma/mapping.c
>
> That's where I firmly disagree. In the DMA API aspect, iommu-dma is exactly 
> a peer of dma-direct,

Exactly.

> however it lives in drivers/iommu for practical 
> reasons because it's more closely coupled to IOMMU API internals in all 
> other aspects of its implementation.

TBH I think kernel/dma/ would be the better place.  But that's really the
least my concernes at the moment.

But the important point is that I would really prefer to avoid another
magic layer - just do direct calls like for dma-direct to keep it
understandable (and probably faster).