Re: [PATCH v2] iommu: iommu_group_claim_dma_owner() must always assign a domain

From: Jason Gunthorpe via iommu <iommu@lists.linux-foundation.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Will Deacon <will@kernel.org>,
	"Tian, Kevin" <kevin.tian@intel.com>,
	"Rodel, Jorg" <jroedel@suse.de>,
	Qian Cai <quic_qiancai@quicinc.com>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>
Subject: Re: [PATCH v2] iommu: iommu_group_claim_dma_owner() must always assign a domain
Date: Fri, 6 May 2022 10:54:31 -0300	[thread overview]
Message-ID: <20220506135431.GC49344@nvidia.com> (raw)
In-Reply-To: <27088ae5-05d6-122a-d9de-80e10eecac38@arm.com>

On Fri, May 06, 2022 at 02:35:50PM +0100, Robin Murphy wrote:

> > So you want to say "DMA is always managed" when attaching a domain of
> > type IOMMU_DOMAIN_UNMANAGED? :)
> 
> Touché ;) Just goes to confirm the point above that confusion between
> general concepts and specific API terms is all too easy. An "unmanaged"
> domain from the PoV of the API just means it's managed by the external
> caller, but you're right that that's not necessarily so obvious either.

Yeah, I'm not so keen on the naming used for IOMMU_DOMAIN_*

I looked for a bit and could not figure out why we need to have
IOMMU_DOMAIN_DMA either.. I didn't find anthing obvious in the iommu
drivers that looked like a special case for this? Most drivers treat
it identically to UNMANAGED in their alloc functions

Only mtk, arm-smmu and some odd stuff in Intel seemed to be sensitive?

> > 	/*
> > 	 * Changing the domain is done by calling attach_dev() on the new
> > 	 * domain. This switch does not have to be atomic and DMA can be
> > 	 * discarded during the transition. DMA must always be translated by
> 
> s/always be translated by/only be able to access/ and we have a deal :)

Done, thanks

Jason
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