hw/acpi: add support for i440fx 'snooping' root busses

If the machine has extra root busses that are snooping to
the i440fx host bridge, we need to add them to
acpi in order to be properly detected by guests.

Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>

hw/i386/acpi-build.c

@@ -626,6 +626,7 @@ build_ssdt(GArray *table_data, GArray *linker,
     uint32_t nr_mem = machine->ram_slots;
     unsigned acpi_cpus = guest_info->apic_id_limit;
     Aml *ssdt, *sb_scope, *scope, *pkg, *dev, *method, *crs, *field, *ifctx;
+    PCIBus *bus = NULL;
     int i;
 
     ssdt = init_aml_allocator();
@@ -637,6 +638,28 @@ build_ssdt(GArray *table_data, GArray *linker,
     /* Reserve space for header */
     acpi_data_push(ssdt->buf, sizeof(AcpiTableHeader));
 
+    /* Extra PCI root buses are implemented  only for i440fx */
+    bus = find_i440fx();
+    if (bus) {
+        QLIST_FOREACH(bus, &bus->child, sibling) {
+            uint8_t bus_num = pci_bus_num(bus);
+
+            /* look only for expander root buses */
+            if (!pci_bus_is_root(bus)) {
+                continue;
+            }
+
+            scope = aml_scope("\\_SB");
+            dev = aml_device("PC%.02X", bus_num);
+            aml_append(dev,
+                       aml_name_decl("_UID", aml_string("PC%.02X", bus_num)));
+            aml_append(dev, aml_name_decl("_HID", aml_string("PNP0A03")));
+            aml_append(dev, aml_name_decl("_BBN", aml_int(bus_num)));
+            aml_append(scope, dev);
+            aml_append(ssdt, scope);
+        }
+    }
+
     scope = aml_scope("\\_SB.PCI0");
     /* build PCI0._CRS */
     crs = aml_resource_template();