Re: [PATCH 12/19] arm64: cpu_ops: Make 'cpu_operations' pointer global instead of per-cpu

'cpu_ops' is an NR_CPUS-length array of 'cpu_operations' pointers, which
theoretically allows for different CPUs to have different bringup and
hotplug backends.

In reality, this complexity exists only to deal with the case where CPU0
is not hotpluggable, so replace the array with a single, global pointer
and record separately whether or not they apply to the boot CPU. Update
the logic in init_cpu_ops() to enforce that only a single set of
'cpu_ops' is required.

Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/cpu_ops.c | 29 ++++++++++++++++++++---------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kernel/cpu_ops.c b/arch/arm64/kernel/cpu_ops.c
index e133011f64b5..eacfb88a0c0c 100644
--- a/arch/arm64/kernel/cpu_ops.c
+++ b/arch/arm64/kernel/cpu_ops.c

@@ -20,7 +20,8 @@ extern const struct cpu_operations acpi_parking_protocol_ops;
 #endif
 extern const struct cpu_operations cpu_psci_ops;
 
-static const struct cpu_operations *cpu_ops[NR_CPUS] __ro_after_init;
+static const struct cpu_operations *cpu_ops __ro_after_init;
+static bool boot_cpu_has_enable_method __ro_after_init;
 
 static const struct cpu_operations *const dt_supported_cpu_ops[] __initconst = {
 	&smp_spin_table_ops,

@@ -40,6 +41,9 @@ static const struct cpu_operations * __init cpu_get_ops(const char *name)
 {
 	const struct cpu_operations *const *ops;
 
+	if (!name)
+		return NULL;
+
 	ops = acpi_disabled ? dt_supported_cpu_ops : acpi_supported_cpu_ops;
 
 	while (*ops) {

@@ -49,6 +53,7 @@ static const struct cpu_operations * __init cpu_get_ops(const char *name)
 		ops++;
 	}
 
+	pr_warn("Unsupported enable-method: %s\n", name);
 	return NULL;
 }
 

@@ -94,25 +99,31 @@ static const char *__init cpu_read_enable_method(int cpu)
 	return enable_method;
 }
 /*
- * Read a cpu's enable method and record it in cpu_ops.
+ * Read a cpu's enable method and update/check cpu_ops.
  */
 int __init init_cpu_ops(int cpu)
 {
 	const char *enable_method = cpu_read_enable_method(cpu);
+	const struct cpu_operations *ops = cpu_get_ops(enable_method);
 
-	if (!enable_method)
+	if (!ops)
 		return -ENODEV;
 
-	cpu_ops[cpu] = cpu_get_ops(enable_method);
-	if (!cpu_ops[cpu]) {
-		pr_warn("Unsupported enable-method: %s\n", enable_method);
-		return -EOPNOTSUPP;
-	}
+	if (!cpu_ops)
+		cpu_ops = ops;
+	else if (cpu_ops != ops)
+		return -EBUSY;