iommu/arm: iommu_add_dt_pci_sideband_ids phantom handling

Handle phantom functions in iommu_add_dt_pci_sideband_ids(). Each phantom
function will have a unique requestor ID (RID)/BDF. On ARM, we need to
map/translate the RID/BDF to an AXI stream ID for each phantom function
according to the pci-iommu device tree mapping [1]. The RID/BDF -> AXI stream ID
mapping in DT could allow phantom devices (i.e. devices with phantom functions)
to use different AXI stream IDs based on the (phantom) function.

[1] https://www.kernel.org/doc/Documentation/devicetree/bindings/pci/pci-iommu.txt

Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

xen/drivers/passthrough/device_tree.c

@@ -169,6 +169,7 @@ int iommu_add_dt_pci_sideband_ids(struct pci_dev *pdev)
     struct device *dev = pci_to_dev(pdev);
     const struct dt_device_node *np;
     int rc;
+    unsigned int devfn = pdev->devfn;
 
     if ( !iommu_enabled )
         return 1;
@@ -183,21 +184,27 @@ int iommu_add_dt_pci_sideband_ids(struct pci_dev *pdev)
     if ( !np )
         return -ENODEV;
 
-    /*
-     * According to the Documentation/devicetree/bindings/pci/pci-iommu.txt
-     * from Linux.
-     */
-    rc = dt_map_id(np, PCI_BDF(pdev->bus, pdev->devfn), "iommu-map",
-                   "iommu-map-mask", &iommu_spec.np, iommu_spec.args);
-    if ( rc )
-        return (rc == -ENODEV) ? 1 : rc;
+    do {
+        /*
+         * According to the Documentation/devicetree/bindings/pci/pci-iommu.txt
+         * from Linux.
+         */
+        rc = dt_map_id(np, PCI_BDF(pdev->bus, devfn), "iommu-map",
+                       "iommu-map-mask", &iommu_spec.np, iommu_spec.args);
+        if ( rc )
+            return (rc == -ENODEV) ? 1 : rc;
 
-    rc = iommu_dt_xlate(dev, &iommu_spec, ops);
-    if ( rc < 0 )
-    {
-        iommu_fwspec_free(dev);
-        return -EINVAL;
+        rc = iommu_dt_xlate(dev, &iommu_spec, ops);
+        if ( rc < 0 )
+        {
+            iommu_fwspec_free(dev);
+            return -EINVAL;
+        }
+
+        devfn += pdev->phantom_stride;
     }
+    while ( (devfn != pdev->devfn) &&
+            (PCI_SLOT(devfn) == PCI_SLOT(pdev->devfn)) );
 
     return rc;
 }