Re: [PATCH v10 10/13] iommu/arm-smmu-v3: Check for SVA features

Jean-Philippe Brucker
2020-09-24T10:15:14Z

Hi Shameer,

On Mon, Sep 21, 2020 at 08:59:39AM +0000, Shameerali Kolothum Thodi wrote:
> > +bool arm_smmu_sva_supported(struct arm_smmu_device *smmu)
> > +{
> > + unsigned long reg, fld;
> > + unsigned long oas;
> > + unsigned long asid_bits;
> > + u32 feat_mask = ARM_SMMU_FEAT_BTM |
> > ARM_SMMU_FEAT_COHERENCY;
>
> Why is BTM mandated for SVA? I couldn't find this requirement in SMMU spec
> (Sorry if I missed it or this got discussed earlier). But if performance is the only concern here,
> is it better just to allow it with a warning rather than limiting SMMUs without BTM?

It's a performance concern and requires to support multiple
configurations, but the spec allows it. Are there SMMUs without BTM that
need it?

Thanks,
Jean