This brings back the ops->detach_dev() code that commit
1b932ceddd19 ("iommu: Remove detach_dev callbacks") deleted and turns it
into an IDENTITY domain.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
  drivers/iommu/arm/arm-smmu/qcom_iommu.c | 39 +++++++++++++++++++++++++
  1 file changed, 39 insertions(+)

diff --git a/drivers/iommu/arm/arm-smmu/qcom_iommu.c b/drivers/iommu/arm/arm-smmu/qcom_iommu.c
index a503ed758ec302..9d7b9d8b4386d4 100644
--- a/drivers/iommu/arm/arm-smmu/qcom_iommu.c
+++ b/drivers/iommu/arm/arm-smmu/qcom_iommu.c

@@ -387,6 +387,44 @@ static int qcom_iommu_attach_dev(struct iommu_domain *domain, struct device *dev
  	return 0;
  }
  
+static int qcom_iommu_identity_attach(struct iommu_domain *identity_domain,
+				      struct device *dev)
+{
+	struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
+	struct qcom_iommu_domain *qcom_domain;
+	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
+	struct qcom_iommu_dev *qcom_iommu = to_iommu(dev);
+	unsigned int i;
+
+	if (domain == identity_domain || !domain)
+		return 0;
+
+	qcom_domain = to_qcom_iommu_domain(domain);
+	if (WARN_ON(!qcom_domain->iommu))
+		return -EINVAL;
+
+	pm_runtime_get_sync(qcom_iommu->dev);
+	for (i = 0; i < fwspec->num_ids; i++) {
+		struct qcom_iommu_ctx *ctx = to_ctx(qcom_domain, fwspec->ids[i]);
+
+		/* Disable the context bank: */
+		iommu_writel(ctx, ARM_SMMU_CB_SCTLR, 0);
+
+		ctx->domain = NULL;

+	}
+	pm_runtime_put_sync(qcom_iommu->dev);
+	return 0;
+}
+
+static struct iommu_domain_ops qcom_iommu_identity_ops = {
+	.attach_dev = qcom_iommu_identity_attach,
+};
+
+static struct iommu_domain qcom_iommu_identity_domain = {
+	.type = IOMMU_DOMAIN_IDENTITY,
+	.ops = &qcom_iommu_identity_ops,
+};
+
  static int qcom_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)

@@ -553,6 +591,7 @@ static int qcom_iommu_of_xlate(struct device *dev, struct of_phandle_args *args)
  }
  
  static const struct iommu_ops qcom_iommu_ops = {
+	.identity_domain = &qcom_iommu_identity_domain,
  	.capable	= qcom_iommu_capable,
  	.domain_alloc	= qcom_iommu_domain_alloc,
  	.probe_device	= qcom_iommu_probe_device,