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>

1 files changed, 23 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index f7a2f81b5b7d..5337ca7bb649 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/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.
  */