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    SubjectRe: [PATCH 2/2] ARM: IOMMU: Tegra30: Add iommu_ops for SMMU driver
    Hi,

    On Tue, Jan 24, 2012 at 02:41:21PM +0100, Hiroshi Doyu wrote:
    > From: Joerg Roedel <joro@8bytes.org>
    > Subject: Re: [PATCH 2/2] ARM: IOMMU: Tegra30: Add iommu_ops for SMMU driver
    > Date: Mon, 23 Jan 2012 16:43:10 +0100
    > Message-ID: <20120123154310.GC6269@8bytes.org>
    >
    > > > + }
    > > > +
    > > > + spin_unlock_irqrestore(&as->lock, flags);
    > > > +
    > > > + domain->priv = NULL;
    > > > + dev_dbg(smmu->dev, "smmu_as@%p\n", as);
    > > > +}
    > > > +
    > > > +static int smmu_iommu_attach_dev(struct iommu_domain *domain,
    > > > + struct device *dev)
    > > > +{
    > > > + struct smmu_as *as = domain->priv;
    > > > + struct smmu_device *smmu = as->smmu;
    > >
    > > Hmm, this looks like there is a 1-1 mapping between hardware SMMU
    > > devices and domains. This is not consistent with IOMMU-API semantics
    > > where a domain can contain devices behind different SMMUs. Please fix
    > > that.
    >
    > Actually I really like the concept of this "domain" now, which hides
    > the H/W hierarchy from users.
    >
    > But in Tegra SMMU/GART case, there's a single one IOMMU device in the
    > system. Keeping a iommu device list in a domain and iterating iommu
    > device list in each iommu_ops seem to be so nice, but I'm afraid that
    > this may be a bit too much when one already knows that there's only
    > one IOMMU device in the system.
    >
    > If there's no actual problem for 1-1 mapping between IOMMU H/Ws and
    > domains, I think that it may not so bad to keep the original code(1-1)
    > for GART and SMMU. What do you think?

    I think it boils down to "extensability". If you can truly/fully
    guarantee that there will *always* be a single IOMMU on all upcoming
    Tegras, then it's really overkill.

    But if there's even a remote possibility of the HW being changed and you
    end up with more IOMMUs, things start to feel necessary for the sake of
    making it easy to extend.

    my 2 cents, feel free to ignore ;-)

    --
    balbi
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