[PATCH RFC] arch_topology: Introduce nr_possible_packages

[Feng Tang]

In multi-sockets platform, kernel or driver code may need the number
of packages for chosing different code directions. Some architecture
already provide such kind of interface like x86, which is being used
in some architecture code and drivers.

Add similar interface 'nr_possible_packages' for platforms which can
get package topology information by parsing ACPI tables in boot phase.

Signed-off-by: Feng Tang <feng.tang@xxxxxxxxxxxxxxxxx>
---
 drivers/base/arch_topology.c  | 21 +++++++++++++++++++++
 include/linux/arch_topology.h |  5 +++++
 2 files changed, 26 insertions(+)

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index 8c5e47c28d9a..796d8a7aceea 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -850,6 +850,16 @@ static bool __init acpi_cpu_is_threaded(int cpu)
 	return !!is_threaded;
 }
 
+unsigned int nr_possible_packages __ro_after_init = 1;
+EXPORT_SYMBOL(nr_possible_packages);
+
+/*
+ * Assuming silicon has a sane package ID decoding method to not have
+ * an ID bigger than 255 (1 byte).
+ */
+#define MAX_PACKAGE_ID	255
+DECLARE_BITMAP(package_id_mask, MAX_PACKAGE_ID + 1);
+
 /*
  * Propagate the topology information of the processor_topology_node tree to the
  * cpu_topology array.
@@ -912,6 +922,13 @@ __weak int __init parse_acpi_topology(void)
 		cpu_topology[cpu].cluster_id = topology_id;
 		topology_id = find_acpi_cpu_topology_package(cpu);
 		cpu_topology[cpu].package_id = topology_id;
+
+
+		if (topology_id >= 0 && topology_id <= MAX_PACKAGE_ID)
+			bitmap_set(package_id_mask, topology_id, 1);
+		else
+			pr_warn("ACPI: abnormal package ID: %d !\n",
+				topology_id);
 	}
 
 	/*
@@ -927,6 +944,10 @@ __weak int __init parse_acpi_topology(void)
 
 	cpu_smt_set_num_threads(max_smt_thread_num, max_smt_thread_num);
 	xa_destroy(&hetero_cpu);
+
+	/* Count the number of possible packages in system */
+	nr_possible_packages = bitmap_weight(package_id_mask, MAX_PACKAGE_ID + 1);
+	pr_info("ACPI: System has %u Package(s) detected\n", nr_possible_packages);
 	return 0;
 }
 
diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
index ebd7f8935f96..dee076cc9c7a 100644
--- a/include/linux/arch_topology.h
+++ b/include/linux/arch_topology.h
@@ -111,4 +111,9 @@ static inline bool topology_core_has_smt(int cpu) { return false; }
 
 #endif /* CONFIG_GENERIC_ARCH_TOPOLOGY */
 
+
+#if defined(CONFIG_ARM64) || defined(CONFIG_RISCV)
+extern unsigned int nr_possible_packages;
+#endif
+
 #endif /* _LINUX_ARCH_TOPOLOGY_H_ */

base-commit: 50897c955902c93ae71c38698abb910525ebdc89
-- 
2.39.5 (Apple Git-154)