arm64: topology: add MPIDR-based detection

Create cpu topology based on MPIDR. When hardware sets MPIDR to sane
values, this method will always work. Therefore it should also work well
as the fallback method. [1]

When we have multiple processing elements in the system, we create
the cpu topology by mapping each affinity level (from lowest to highest)
to threads (if they exist), cores, and clusters.

[1] http://www.spinics.net/lists/arm-kernel/msg317445.html

Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Zi Shen Lim <zlim@broadcom.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/cputype.h

@@ -18,6 +18,8 @@
 
 #define INVALID_HWID		ULONG_MAX
 
+#define MPIDR_UP_BITMASK	(0x1 << 30)
+#define MPIDR_MT_BITMASK	(0x1 << 24)
 #define MPIDR_HWID_BITMASK	0xff00ffffff
 
 #define MPIDR_LEVEL_BITS_SHIFT	3

arch/arm64/kernel/topology.c

@@ -20,6 +20,7 @@
 #include <linux/of.h>
 #include <linux/sched.h>
 
+#include <asm/cputype.h>
 #include <asm/topology.h>
 
 static int __init get_cpu_for_node(struct device_node *node)
@@ -188,13 +189,9 @@ static int __init parse_dt_topology(void)
 	 * Check that all cores are in the topology; the SMP code will
 	 * only mark cores described in the DT as possible.
 	 */
-	for_each_possible_cpu(cpu) {
-		if (cpu_topology[cpu].cluster_id == -1) {
-			pr_err("CPU%d: No topology information specified\n",
-			       cpu);
+	for_each_possible_cpu(cpu)
+		if (cpu_topology[cpu].cluster_id == -1)
 			ret = -EINVAL;
-		}
-	}
 
 out_map:
 	of_node_put(map);
@@ -219,14 +216,6 @@ static void update_siblings_masks(unsigned int cpuid)
 	struct cpu_topology *cpu_topo, *cpuid_topo = &cpu_topology[cpuid];
 	int cpu;
 
-	if (cpuid_topo->cluster_id == -1) {
-		/*
-		 * DT does not contain topology information for this cpu.
-		 */
-		pr_debug("CPU%u: No topology information configured\n", cpuid);
-		return;
-	}
-
 	/* update core and thread sibling masks */
 	for_each_possible_cpu(cpu) {
 		cpu_topo = &cpu_topology[cpu];
@@ -249,6 +238,36 @@ static void update_siblings_masks(unsigned int cpuid)
 
 void store_cpu_topology(unsigned int cpuid)
 {
+	struct cpu_topology *cpuid_topo = &cpu_topology[cpuid];
+	u64 mpidr;
+
+	if (cpuid_topo->cluster_id != -1)
+		goto topology_populated;
+
+	mpidr = read_cpuid_mpidr();
+
+	/* Uniprocessor systems can rely on default topology values */
+	if (mpidr & MPIDR_UP_BITMASK)
+		return;
+
+	/* Create cpu topology mapping based on MPIDR. */
+	if (mpidr & MPIDR_MT_BITMASK) {
+		/* Multiprocessor system : Multi-threads per core */
+		cpuid_topo->thread_id  = MPIDR_AFFINITY_LEVEL(mpidr, 0);
+		cpuid_topo->core_id    = MPIDR_AFFINITY_LEVEL(mpidr, 1);
+		cpuid_topo->cluster_id = MPIDR_AFFINITY_LEVEL(mpidr, 2);
+	} else {
+		/* Multiprocessor system : Single-thread per core */
+		cpuid_topo->thread_id  = -1;
+		cpuid_topo->core_id    = MPIDR_AFFINITY_LEVEL(mpidr, 0);
+		cpuid_topo->cluster_id = MPIDR_AFFINITY_LEVEL(mpidr, 1);
+	}
+
+	pr_debug("CPU%u: cluster %d core %d thread %d mpidr %#016llx\n",
+		 cpuid, cpuid_topo->cluster_id, cpuid_topo->core_id,
+		 cpuid_topo->thread_id, mpidr);
+
+topology_populated:
 	update_siblings_masks(cpuid);
 }