pc-dimm: introduce realize callback

nvdimm needs to  check if the backend memory is large enough to contain
label data and init its memory region when the device is realized, so
introduce realize callback which is called after common dimm has been
realize

Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

hw/mem/pc-dimm.c

@@ -400,6 +400,7 @@ static void pc_dimm_init(Object *obj)
 static void pc_dimm_realize(DeviceState *dev, Error **errp)
 {
     PCDIMMDevice *dimm = PC_DIMM(dev);
+    PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
 
     if (!dimm->hostmem) {
         error_setg(errp, "'" PC_DIMM_MEMDEV_PROP "' property is not set");
@@ -412,6 +413,10 @@ static void pc_dimm_realize(DeviceState *dev, Error **errp)
                    dimm->node, nb_numa_nodes ? nb_numa_nodes : 1);
         return;
     }
+
+    if (ddc->realize) {
+        ddc->realize(dimm, errp);
+    }
 }
 
 static MemoryRegion *pc_dimm_get_memory_region(PCDIMMDevice *dimm)

include/hw/mem/pc-dimm.h

@@ -58,6 +58,8 @@ typedef struct PCDIMMDevice {
 
 /**
  * PCDIMMDeviceClass:
+ * @realize: called after common dimm is realized so that the dimm based
+ * devices get the chance to do specified operations.
  * @get_memory_region: returns #MemoryRegion associated with @dimm which
  * is directly mapped into the physical address space of guest
  */
@@ -66,6 +68,7 @@ typedef struct PCDIMMDeviceClass {
     DeviceClass parent_class;
 
     /* public */
+    void (*realize)(PCDIMMDevice *dimm, Error **errp);
     MemoryRegion *(*get_memory_region)(PCDIMMDevice *dimm);
 } PCDIMMDeviceClass;