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: [ref]

quoted

+	}
+
+	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?