hw/core: explicit OFW unit address callback for SysBusDeviceClass

The sysbus_get_fw_dev_path() function formats OpenFirmware device path
nodes ("driver-name@unit-address") for sysbus devices. The first choice
for "unit-address" is the base address of the device's first MMIO region.
The second choice is its first IO port.

However, if two sysbus devices with the same "driver-name" lack both MMIO
and PIO resources, then there is no good way to distinguish them based on
their OFW nodes, because in this case unit-address is omitted completely
for both devices. An example is TYPE_PXB_HOST ("pxb-host").

For the sake of such devices, introduce the explicit_ofw_unit_address()
"virtual member function". With this function, each sysbus device in the
same SysBusDeviceClass can state its own address.

Cc: Markus Armbruster <armbru@redhat.com>
Cc: Marcel Apfelbaum <marcel@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: NLaszlo Ersek <lersek@redhat.com>
Reviewed-by: NMarcel Apfelbaum <marcel@redhat.com>
Tested-by: NMarcel Apfelbaum <marcel@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/core/sysbus.c

@@ -281,6 +281,9 @@ static void sysbus_dev_print(Monitor *mon, DeviceState *dev, int indent)
 static char *sysbus_get_fw_dev_path(DeviceState *dev)
 {
     SysBusDevice *s = SYS_BUS_DEVICE(dev);
+    SysBusDeviceClass *sbc = SYS_BUS_DEVICE_GET_CLASS(s);
+    /* for the explicit unit address fallback case: */
+    char *addr, *fw_dev_path;
 
     if (s->num_mmio) {
         return g_strdup_printf("%s@" TARGET_FMT_plx, qdev_fw_name(dev),
@@ -289,6 +292,14 @@ static char *sysbus_get_fw_dev_path(DeviceState *dev)
     if (s->num_pio) {
         return g_strdup_printf("%s@i%04x", qdev_fw_name(dev), s->pio[0]);
     }
+    if (sbc->explicit_ofw_unit_address) {
+        addr = sbc->explicit_ofw_unit_address(s);
+        if (addr) {
+            fw_dev_path = g_strdup_printf("%s@%s", qdev_fw_name(dev), addr);
+            g_free(addr);
+            return fw_dev_path;
+        }
+    }
     return g_strdup(qdev_fw_name(dev));
 }
 

include/hw/sysbus.h

@@ -41,6 +41,23 @@ typedef struct SysBusDeviceClass {
     /*< public >*/
 
     int (*init)(SysBusDevice *dev);
+
+    /*
+     * Let the sysbus device format its own non-PIO, non-MMIO unit address.
+     *
+     * Sometimes a class of SysBusDevices has neither MMIO nor PIO resources,
+     * yet instances of it would like to distinguish themselves, in
+     * OpenFirmware device paths, from other instances of the same class on the
+     * sysbus. For that end we expose this callback.
+     *
+     * The implementation is not supposed to change *@dev, or incur other
+     * observable change.
+     *
+     * The function returns a dynamically allocated string. On error, NULL
+     * should be returned; the unit address portion of the OFW node will be
+     * omitted then. (This is not considered a fatal error.)
+     */
+    char *(*explicit_ofw_unit_address)(const SysBusDevice *dev);
 } SysBusDeviceClass;
 
 struct SysBusDevice {