powerpc: Make core id information available to userspace

Existing Open Firmware practice is to report each processor core as a
separate node in the device tree.  Report the value of the "reg" OF
property corresponding to a logical CPU's device node as the core_id
attribute in /sys/devices/system/cpu/cpu*/topology/core_id.
Signed-off-by: Nathan Lynch <ntl@pobox.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/smp.c

@@ -380,6 +380,29 @@ int __cpuinit __cpu_up(unsigned int cpu)
 	return 0;
 }
 
+/* Return the value of the reg property corresponding to the given
+ * logical cpu.
+ */
+int cpu_to_core_id(int cpu)
+{
+	struct device_node *np;
+	const int *reg;
+	int id = -1;
+
+	np = of_get_cpu_node(cpu, NULL);
+	if (!np)
+		goto out;
+
+	reg = of_get_property(np, "reg", NULL);
+	if (!reg)
+		goto out;
+
+	id = *reg;
+out:
+	of_node_put(np);
+	return id;
+}
+
 /* Must be called when no change can occur to cpu_present_map,
  * i.e. during cpu online or offline.
  */

include/asm-powerpc/smp.h

@@ -63,6 +63,7 @@ extern int smp_hw_index[];
 
 DECLARE_PER_CPU(cpumask_t, cpu_sibling_map);
 DECLARE_PER_CPU(cpumask_t, cpu_core_map);
+extern int cpu_to_core_id(int cpu);
 
 /* Since OpenPIC has only 4 IPIs, we use slightly different message numbers.
  *

include/asm-powerpc/topology.h

@@ -109,6 +109,7 @@ static inline void sysfs_remove_device_from_node(struct sys_device *dev,
 
 #define topology_thread_siblings(cpu)	(per_cpu(cpu_sibling_map, cpu))
 #define topology_core_siblings(cpu)	(per_cpu(cpu_core_map, cpu))
+#define topology_core_id(cpu)		(cpu_to_core_id(cpu))
 #endif
 #endif