Merge tag 'smp-core-2024-09-16' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull CPU hotplug updates from Thomas Gleixner:

 - Prepare the core for supporting parallel hotplug on loongarch

 - A small set of cleanups and enhancements

* tag 'smp-core-2024-09-16' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  smp: Mark smp_prepare_boot_cpu() __init
  cpu: Fix W=1 build kernel-doc warning
  cpu/hotplug: Provide weak fallback for arch_cpuhp_init_parallel_bringup()
  cpu/hotplug: Make HOTPLUG_PARALLEL independent of HOTPLUG_SMT

Author: torvalds

arch/mips/kernel/smp.c

@@ -439,7 +439,7 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
 }
 
 /* preload SMP state for boot cpu */
-void smp_prepare_boot_cpu(void)
+void __init smp_prepare_boot_cpu(void)
 {
 	if (mp_ops->prepare_boot_cpu)
 		mp_ops->prepare_boot_cpu();

arch/powerpc/kernel/smp.c

@@ -1166,7 +1166,7 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
 	cpu_smt_set_num_threads(num_threads, threads_per_core);
 }
 
-void smp_prepare_boot_cpu(void)
+void __init smp_prepare_boot_cpu(void)
 {
 	BUG_ON(smp_processor_id() != boot_cpuid);
 #ifdef CONFIG_PPC64

include/linux/smp.h

@@ -109,7 +109,7 @@ static inline void on_each_cpu_cond(smp_cond_func_t cond_func,
  * Architecture specific boot CPU setup.  Defined as empty weak function in
  * init/main.c. Architectures can override it.
  */
-void smp_prepare_boot_cpu(void);
+void __init smp_prepare_boot_cpu(void);
 
 #ifdef CONFIG_SMP
 

kernel/cpu.c

@@ -1808,6 +1808,7 @@ static int __init parallel_bringup_parse_param(char *arg)
 }
 early_param("cpuhp.parallel", parallel_bringup_parse_param);
 
+#ifdef CONFIG_HOTPLUG_SMT
 static inline bool cpuhp_smt_aware(void)
 {
 	return cpu_smt_max_threads > 1;
@@ -1817,6 +1818,21 @@ static inline const struct cpumask *cpuhp_get_primary_thread_mask(void)
 {
 	return cpu_primary_thread_mask;
 }
+#else
+static inline bool cpuhp_smt_aware(void)
+{
+	return false;
+}
+static inline const struct cpumask *cpuhp_get_primary_thread_mask(void)
+{
+	return cpu_none_mask;
+}
+#endif
+
+bool __weak arch_cpuhp_init_parallel_bringup(void)
+{
+	return true;
+}
 
 /*
  * On architectures which have enabled parallel bringup this invokes all BP
@@ -2689,9 +2705,7 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
 	return ret;
 }
 
-/**
- * Check if the core a CPU belongs to is online
- */
+/* Check if the core a CPU belongs to is online */
 #if !defined(topology_is_core_online)
 static inline bool topology_is_core_online(unsigned int cpu)
 {