iommu: Add IOMMU_DOMAIN_PLATFORM for S390

The PLATFORM domain will be set as the default domain and attached as
normal during probe. The driver will ignore the initial attach from a NULL
domain to the PLATFORM domain.

After this, the PLATFORM domain's attach_dev will be called whenever we
detach from an UNMANAGED domain (eg for VFIO). This is the same time the
original design would have called op->detach_dev().

This is temporary until the S390 dma-iommu.c conversion is merged.

Tested-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
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/4-v8-81230027b2fa+9d-iommu_all_defdom_jgg@nvidia.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/s390-iommu.c

@@ -142,14 +142,31 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
 	return 0;
 }
 
-static void s390_iommu_set_platform_dma(struct device *dev)
+/*
+ * Switch control over the IOMMU to S390's internal dma_api ops
+ */
+static int s390_iommu_platform_attach(struct iommu_domain *platform_domain,
+				      struct device *dev)
 {
 	struct zpci_dev *zdev = to_zpci_dev(dev);
 
+	if (!zdev->s390_domain)
+		return 0;
+
 	__s390_iommu_detach_device(zdev);
 	zpci_dma_init_device(zdev);
+	return 0;
 }
 
+static struct iommu_domain_ops s390_iommu_platform_ops = {
+	.attach_dev = s390_iommu_platform_attach,
+};
+
+static struct iommu_domain s390_iommu_platform_domain = {
+	.type = IOMMU_DOMAIN_PLATFORM,
+	.ops = &s390_iommu_platform_ops,
+};
+
 static void s390_iommu_get_resv_regions(struct device *dev,
 					struct list_head *list)
 {
@@ -428,12 +445,12 @@ void zpci_destroy_iommu(struct zpci_dev *zdev)
 }
 
 static const struct iommu_ops s390_iommu_ops = {
+	.default_domain = &s390_iommu_platform_domain,
 	.capable = s390_iommu_capable,
 	.domain_alloc = s390_domain_alloc,
 	.probe_device = s390_iommu_probe_device,
 	.release_device = s390_iommu_release_device,
 	.device_group = generic_device_group,
-	.set_platform_dma_ops = s390_iommu_set_platform_dma,
 	.pgsize_bitmap = SZ_4K,
 	.get_resv_regions = s390_iommu_get_resv_regions,
 	.default_domain_ops = &(const struct iommu_domain_ops) {