iommu/mtk_iommu: Add an IOMMU_IDENTITIY_DOMAIN

This brings back the ops->detach_dev() code that commit
1b932ced ("iommu: Remove detach_dev callbacks") deleted and turns it
into an IDENTITY domain.
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/18-v8-81230027b2fa+9d-iommu_all_defdom_jgg@nvidia.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/mtk_iommu.c

@@ -777,6 +777,28 @@ static int mtk_iommu_attach_device(struct iommu_domain *domain,
 	return ret;
 }
 
+static int mtk_iommu_identity_attach(struct iommu_domain *identity_domain,
+				     struct device *dev)
+{
+	struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
+	struct mtk_iommu_data *data = dev_iommu_priv_get(dev);
+
+	if (domain == identity_domain || !domain)
+		return 0;
+
+	mtk_iommu_config(data, dev, false, 0);
+	return 0;
+}
+
+static struct iommu_domain_ops mtk_iommu_identity_ops = {
+	.attach_dev = mtk_iommu_identity_attach,
+};
+
+static struct iommu_domain mtk_iommu_identity_domain = {
+	.type = IOMMU_DOMAIN_IDENTITY,
+	.ops = &mtk_iommu_identity_ops,
+};
+
 static int mtk_iommu_map(struct iommu_domain *domain, unsigned long iova,
 			 phys_addr_t paddr, size_t pgsize, size_t pgcount,
 			 int prot, gfp_t gfp, size_t *mapped)
@@ -996,6 +1018,7 @@ static void mtk_iommu_get_resv_regions(struct device *dev,
 }
 
 static const struct iommu_ops mtk_iommu_ops = {
+	.identity_domain = &mtk_iommu_identity_domain,
 	.domain_alloc	= mtk_iommu_domain_alloc,
 	.probe_device	= mtk_iommu_probe_device,
 	.release_device	= mtk_iommu_release_device,