xen/smmu: Add remove_device callback for smmu_iommu ops

Add remove_device callback for removing the device entry from smmu-master using
following steps:
1. Find if SMMU master exists for the device node.
2. Check if device is currently in use.
3. Remove the SMMU master.

Signed-off-by: Vikram Garhwal <vikram.garhwal@amd.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

xen/drivers/passthrough/arm/smmu.c

@@ -815,6 +815,19 @@ static int insert_smmu_master(struct arm_smmu_device *smmu,
 	return 0;
 }
 
+static int remove_smmu_master(struct arm_smmu_device *smmu,
+			      struct arm_smmu_master *master)
+{
+	if (!smmu->masters.rb_node) {
+		ASSERT_UNREACHABLE();
+		return -ENOENT;
+	}
+
+	rb_erase(&master->node, &smmu->masters);
+
+	return 0;
+}
+
 static int arm_smmu_dt_add_device_legacy(struct arm_smmu_device *smmu,
 					 struct device *dev,
 					 struct iommu_fwspec *fwspec)
@@ -852,6 +865,32 @@ static int arm_smmu_dt_add_device_legacy(struct arm_smmu_device *smmu,
 	return insert_smmu_master(smmu, master);
 }
 
+static int arm_smmu_dt_remove_device_legacy(struct arm_smmu_device *smmu,
+					 struct device *dev)
+{
+	struct arm_smmu_master *master;
+	struct device_node *dev_node = dev_get_dev_node(dev);
+	int ret;
+
+	master = find_smmu_master(smmu, dev_node);
+	if (master == NULL) {
+		dev_err(dev,
+			"No registrations found for master device %s\n",
+			dev_node->name);
+		return -EINVAL;
+	}
+
+	ret = remove_smmu_master(smmu, master);
+	if (ret)
+		return ret;
+
+	/* Protected by dt_host_lock and dtdevs_lock as caller holds these locks. */
+	dev_node->is_protected = false;
+
+	kfree(master);
+	return 0;
+}
+
 static int register_smmu_master(struct arm_smmu_device *smmu,
 				struct device *dev,
 				struct of_phandle_args *masterspec)
@@ -875,6 +914,26 @@ static int register_smmu_master(struct arm_smmu_device *smmu,
 					     fwspec);
 }
 
+/*
+ * The driver which supports generic IOMMU DT bindings must have this
+ * callback implemented.
+ */
+static int arm_smmu_dt_remove_device_generic(u8 devfn, struct device *dev)
+{
+	struct arm_smmu_device *smmu;
+	struct iommu_fwspec *fwspec;
+
+	fwspec = dev_iommu_fwspec_get(dev);
+	if (fwspec == NULL)
+		return -ENXIO;
+
+	smmu = find_smmu(fwspec->iommu_dev);
+	if (smmu == NULL)
+		return -ENXIO;
+
+	return arm_smmu_dt_remove_device_legacy(smmu, dev);
+}
+
 static int arm_smmu_dt_add_device_generic(u8 devfn, struct device *dev)
 {
 	struct arm_smmu_device *smmu;
@@ -2859,6 +2918,7 @@ static const struct iommu_ops arm_smmu_iommu_ops = {
     .init = arm_smmu_iommu_domain_init,
     .hwdom_init = arch_iommu_hwdom_init,
     .add_device = arm_smmu_dt_add_device_generic,
+    .remove_device = arm_smmu_dt_remove_device_generic,
     .teardown = arm_smmu_iommu_domain_teardown,
     .iotlb_flush = arm_smmu_iotlb_flush,
     .assign_device = arm_smmu_assign_dev,