powerpc/powernv: Add helper to get ibm,chip-id of a node

This includes walking the parent nodes if necessary.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/prom.h

@@ -58,6 +58,8 @@ static inline int of_node_to_nid(struct device_node *device) { return 0; }
 
 extern void of_instantiate_rtc(void);
 
+extern int of_get_ibm_chip_id(struct device_node *np);
+
 /* The of_drconf_cell struct defines the layout of the LMB array
  * specified in the device tree property
  * ibm,dynamic-reconfiguration-memory/ibm,dynamic-memory

arch/powerpc/kernel/prom.c

@@ -795,6 +795,32 @@ struct device_node *of_find_next_cache_node(struct device_node *np)
 	return NULL;
 }
 
+/**
+ * of_get_ibm_chip_id - Returns the IBM "chip-id" of a device
+ * @np: device node of the device
+ *
+ * This looks for a property "ibm,chip-id" in the node or any
+ * of its parents and returns its content, or -1 if it cannot
+ * be found.
+ */
+int of_get_ibm_chip_id(struct device_node *np)
+{
+	of_node_get(np);
+	while(np) {
+		struct device_node *old = np;
+		const __be32 *prop;
+
+		prop = of_get_property(np, "ibm,chip-id", NULL);
+		if (prop) {
+			of_node_put(np);
+			return be32_to_cpup(prop);
+		}
+		np = of_get_parent(np);
+		of_node_put(old);
+	}
+	return -1;
+}
+
 #ifdef CONFIG_PPC_PSERIES
 /*
  * Fix up the uninitialized fields in a new device node: