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Date:   Fri, 24 Mar 2023 10:50:34 -0700
From:   Nicolin Chen <nicolinc@nvidia.com>
To:     Eric Auger <eric.auger@redhat.com>
CC:     <jgg@nvidia.com>, <robin.murphy@arm.com>, <will@kernel.org>,
        <kevin.tian@intel.com>, <baolu.lu@linux.intel.com>,
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        <jean-philippe@linaro.org>, <linux-arm-kernel@lists.infradead.org>,
        <iommu@lists.linux.dev>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v1 12/14] iommu/arm-smmu-v3: Support IOMMU_DOMAIN_NESTED
 type of allocations
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On Fri, Mar 24, 2023 at 04:44:58PM +0100, Eric Auger wrote:
> > @@ -2923,8 +2949,16 @@ arm_smmu_domain_alloc_user(struct device *dev, struct iommu_domain *parent,
> >       const struct iommu_hwpt_arm_smmuv3 *user_cfg = user_data;
> >       struct arm_smmu_master *master = dev_iommu_priv_get(dev);
> >       unsigned type = IOMMU_DOMAIN_UNMANAGED;
> > +     struct arm_smmu_domain *s2 = NULL;
> > +
> > +     if (parent) {
> > +             if (parent->ops != arm_smmu_ops.default_domain_ops)
> > +                     return NULL;
> > +             type = IOMMU_DOMAIN_NESTED;
> > +             s2 = to_smmu_domain(parent);
> > +     }
> Please can you explain the (use) case where !parent. This creates an
> unmanaged S1?

It creates an unmanaged type of a domain. The decision to mark
it as an unmanaged S1 or an unmanaged S2 domain, is done in the
finalise() function that it checks the S2 flag and set a stage
accordingly.

I think that I could add a few lines of comments inline or at
the top of the function to ease the readability.

Thanks
Nicolin