[RFC PATCH 3/3] arm64: topology: Use PPTT to determine if PE is a thread

[John Garry <john.garry@xxxxxxxxxx>]

From: Jeremy Linton <jeremy.linton@xxxxxxx>

Commit 98dc19902a0b2e5348e43d6a2c39a0a7d0fc639e upstream.

ACPI 6.3 adds a thread flag to represent if a CPU/PE is
actually a thread. Given that the MPIDR_MT bit may not
represent this information consistently on homogeneous machines
we should prefer the PPTT flag if its available.

Signed-off-by: Jeremy Linton <jeremy.linton@xxxxxxx>
Reviewed-by: Sudeep Holla <sudeep.holla@xxxxxxx>
Reviewed-by: Robert Richter <rrichter@xxxxxxxxxxx>
[will: made acpi_cpu_is_threaded() return 'bool']
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: John Garry <john.garry@xxxxxxxxxx>
---
 arch/arm64/kernel/topology.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 0825c4a856e3..6106c49f84bc 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -340,17 +340,28 @@ void remove_cpu_topology(unsigned int cpu)
 }
 
 #ifdef CONFIG_ACPI
+static bool __init acpi_cpu_is_threaded(int cpu)
+{
+	int is_threaded = acpi_pptt_cpu_is_thread(cpu);
+
+	/*
+	 * if the PPTT doesn't have thread information, assume a homogeneous
+	 * machine and return the current CPU's thread state.
+	 */
+	if (is_threaded < 0)
+		is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK;
+
+	return !!is_threaded;
+}
+
 /*
  * Propagate the topology information of the processor_topology_node tree to the
  * cpu_topology array.
  */
 static int __init parse_acpi_topology(void)
 {
-	bool is_threaded;
 	int cpu, topology_id;
 
-	is_threaded = read_cpuid_mpidr() & MPIDR_MT_BITMASK;
-
 	for_each_possible_cpu(cpu) {
 		int i, cache_id;
 
@@ -358,7 +369,7 @@ static int __init parse_acpi_topology(void)
 		if (topology_id < 0)
 			return topology_id;
 
-		if (is_threaded) {
+		if (acpi_cpu_is_threaded(cpu)) {
 			cpu_topology[cpu].thread_id = topology_id;
 			topology_id = find_acpi_cpu_topology(cpu, 1);
 			cpu_topology[cpu].core_id   = topology_id;
-- 
2.17.1