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Subject: Re: [PATCH 12/18] iommu/tegra-gart: Add IOMMU_DOMAIN_DMA support
To:     Robin Murphy <robin.murphy@arm.com>, hch@lst.de, joro@8bytes.org,
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Date:   Mon, 24 Aug 2020 00:42:02 +0300
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21.08.2020 03:28, Robin Murphy пишет:
...
>> Will a returned NULL tell to IOMMU core that implicit domain shouldn't
>> be used? Is it possible to leave this driver as-is?
> 
> The aim of this patch was just to make the conversion without functional
> changes wherever possible, i.e. maintain an equivalent to the existing
> ARM behaviour of allocating its own implicit domains for everything. It
> doesn't represent any judgement of whether that was ever appropriate for
> this driver in the first place ;)
> 
> Hopefully my other reply already covered the degree of control drivers
> can have with proper default domains, but do shout if anything wasn't
> clear.

Thank you for the detailed comments! I wasn't watching closely all the
recent iommu/ changes and yours clarification is very helpful!

My current understanding is that the GART driver will need to support
the IOMMU_DOMAIN_IDENTITY and set def_domain_type to
IOMMU_DOMAIN_IDENTITY for all devices.

Meanwhile, today's upstream drivers don't use GART, hence this patch
should be okay. Although, it's a bit unlikely that the IOMMU_DOMAIN_DMA
type will ever be useful for the GART, and thus, I'm still thinking that
will be a bit nicer to keep GART driver as-is for now.