[PATCHv2 2/2] arm64: topology: add MPIDR-based detection

[Zi Shen Lim]

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.

We combine data from all higher affinity levels into cluster_id
so we don't lose any information from MPIDR. [2]

[1] http://www.spinics.net/lists/arm-kernel/msg317445.html
[2] https://lkml.org/lkml/2014/4/23/703

Signed-off-by: Zi Shen Lim <zlim at broadcom.com>
---
v1->v2: Addressed comments from Mark Brown.
 - Reduce noise. Use pr_debug instead of pr_info.
 - Don't ignore higher affinity levels.

 arch/arm64/include/asm/cputype.h |  2 ++
 arch/arm64/kernel/topology.c     | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/arch/arm64/include/asm/cputype.h b/arch/arm64/include/asm/cputype.h
index c404fb0..7639e8b 100644
--- a/arch/arm64/include/asm/cputype.h
+++ b/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
diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 3e06b0b..7dbf981 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -19,6 +19,8 @@
 #include <linux/nodemask.h>
 #include <linux/sched.h>
 
+#include <asm/cputype.h>
+#include <asm/smp_plat.h>
 #include <asm/topology.h>
 
 /*
@@ -71,6 +73,38 @@ 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;
+
+	mpidr = read_cpuid_mpidr();
+
+	/* Create cpu topology mapping based on MPIDR. */
+	if (mpidr & MPIDR_UP_BITMASK) {
+		/* Uniprocessor system */
+		cpuid_topo->thread_id  = -1;
+		cpuid_topo->core_id    = MPIDR_AFFINITY_LEVEL(mpidr, 0);
+		cpuid_topo->cluster_id = -1;
+	} else 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) |
+			MPIDR_AFFINITY_LEVEL(mpidr, 3) << mpidr_hash.shift_aff[3];
+	} 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) |
+			MPIDR_AFFINITY_LEVEL(mpidr, 2) << mpidr_hash.shift_aff[2] |
+			MPIDR_AFFINITY_LEVEL(mpidr, 3) << mpidr_hash.shift_aff[3];
+	}
+
+	pr_debug("CPU%u: cluster %d core %d thread %d mpidr %llx\n",
+		 cpuid, cpuid_topo->cluster_id, cpuid_topo->core_id,
+		 cpuid_topo->thread_id, mpidr);
+
 	update_siblings_masks(cpuid);
 }
 
-- 
1.8.4.3