Re: [Xen-devel] [PATCH RFC] Add SUPPORT.md

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

Sorry I missed e-mail. It seems I was not CCed on it.

On 07/09/17 22:36, Stefano Stabellini wrote:
> On Thu, 31 Aug 2017, Roger Pau Monne wrote:
> > > +### ARM/Non-PCI device passthrough
> > > +
> > > +    Status: Supported
> > I guess non-pci devices on ARM also use the IOMMU? (SMMU)
> Yes, they do.
>
>
> > > +### ARM/SMMU
> > > +
> > > +    Status: Supported, with caveats
> > > +
> > > +Only ARM SMMU hardware is supported; non-ARM SMMU hardware is not supported.
> > I'm not sure of the purpose of this sentence, it's quite clear that
> > the SMMU is only supported if available. Also, I'm not sure this
> > should be spelled out in this document, x86 doesn't have a VT-d or SVM
> > section.
> As George wrote, there are many SMMUs in the market for ARM based
> platforms, not all of them of ARM design.
Few remarks here.

Firstly, what do you mean by Arm design? Is it spec compliant (i.e 
SMMUv1, SMMUv2, SMMUv3) ? Or is it implementation coming from Arm 
(SMMU-400, SMMU-401, SMMU-500,...)?
At the moment we have no support of SMMUv3 at all (this would be a 
separate driver as the spec is very different).
Regarding SMMUv1 and SMMUv2. Technically we should support all SMMUs 
which are compliant with the spec, providing there are no workaround 
necessary (yes there are some hardware only 99.9% compliant).
But, we can't even claim that we support Arm implementation. At least 
SMMU-401 (used by Seattle and Versatile Express) is not supported.
Furthermore, Arm may release new IP in the future. Does it mean we 
support them by default?
So there are some clarifications needed on what we actually support.

If we decide the support status is based on hardware, then it raise the 
questions on what about other specifications (e.g GICv2, GICv3, GICv4)? 
Each vendor is free to provide its own implementation (not necessarily 
bug free and fully compliant).
Cheers,

--
Julien Grall

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