Re: [PATCH 1/2] powerpc: Detect the presence of big-core with interleaved threads

diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
index 0af5c11..884dff2 100644
--- a/arch/powerpc/kernel/setup-common.c
+++ b/arch/powerpc/kernel/setup-common.c

@@ -436,8 +438,56 @@ static void __init cpu_init_thread_core_maps(int tpc)
 	printk(KERN_DEBUG " (thread shift is %d)\n", threads_shift);
 }
 
-
 u32 *cpu_to_phys_id = NULL;
+/*
+ * check_for_interleaved_big_core - Checks if the core represented by
+ *	 dn is a big-core whose threads are interleavings of the
+ *	 threads of the component small cores.
+ *
+ * @dn: device node corresponding to the core.
+ *
+ * Returns true if the core is a interleaved big-core.
+ * Returns false otherwise.
+ */
+static inline bool check_for_interleaved_big_core(struct device_node *dn)
+{
+	int len, nr_groups, threads_per_group;
+	const __be32 *thread_groups;
+	__be32 *thread_list, *first_cpu_idx;
+	int cur_cpu, next_cpu, i, j;
+
+	thread_groups = of_get_property(dn, "ibm,thread-groups", &len);
+	if (!thread_groups)
+		return false;

+
+	threads_per_group = be32_to_cpu(*(thread_groups + 2));
+	thread_list = (__be32 *)thread_groups + 3;
+
+	/*
+	 * In case of an interleaved big-core, the thread-ids of the
+	 * big-core can be obtained by interleaving the the thread-ids
+	 * of the component small
+	 *
+	 * Eg: On a 8-thread big-core with two SMT4 small cores, the
+	 * threads of the two component small cores will be
+	 * {0, 2, 4, 6} and {1, 3, 5, 7}.
+	 */
+	for (i = 0; i < nr_groups; i++) {
+		first_cpu_idx = thread_list + i * threads_per_group;
+
+		for (j = 0; j < threads_per_group - 1; j++) {
+			cur_cpu = be32_to_cpu(*(first_cpu_idx + j));
+			next_cpu = be32_to_cpu(*(first_cpu_idx + j + 1));
+			if (next_cpu != cur_cpu + nr_groups)
+				return false;
+		}
+	}
+	return true;
+}
 
 /**
  * setup_cpu_maps - initialize the following cpu maps:

@@ -565,7 +615,16 @@ void __init smp_setup_cpu_maps(void)
 	vdso_data->processorCount = num_present_cpus();
 #endif /* CONFIG_PPC64 */
 
-        /* Initialize CPU <=> thread mapping/
+	dn = of_find_node_by_type(NULL, "cpu");
+	if (dn) {
+		if (check_for_interleaved_big_core(dn)) {
+			has_interleaved_big_core = true;
+			pr_info("Detected interleaved big-cores\n");
+		}
+		of_node_put(dn);
+	}