[PATCH 4/4] arm64: Dereference CPU operations indirectly

[Gavin Shan <gshan@redhat.com>]

One CPU operations is maintained through array @cpu_ops[NR_CPUS]. 2KB
memory is consumed when CONFIG_NR_CPUS is set to 256. It seems too
much memory has been used for this.

This introduces another array (@cpu_ops_index[NR_CPUS]), of which the
index to CPU operations array is stored. With this, we just one byte
for each CPU, 256 bytes for 256 CPUs, to dereference the CPU operations
indirectly.

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 arch/arm64/kernel/cpu_ops.c | 44 +++++++++++++++++++++----------------
 1 file changed, 25 insertions(+), 19 deletions(-)

diff --git a/arch/arm64/kernel/cpu_ops.c b/arch/arm64/kernel/cpu_ops.c
index e133011f64b5..2a58222a2f24 100644
--- a/arch/arm64/kernel/cpu_ops.c
+++ b/arch/arm64/kernel/cpu_ops.c
@@ -20,39 +20,33 @@ 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 *const dt_supported_cpu_ops[] __initconst = {
+static const struct cpu_operations *const cpu_ops[] = {
 	&smp_spin_table_ops,
-	&cpu_psci_ops,
-	NULL,
-};
-
-static const struct cpu_operations *const acpi_supported_cpu_ops[] __initconst = {
 #ifdef CONFIG_ARM64_ACPI_PARKING_PROTOCOL
 	&acpi_parking_protocol_ops,
 #endif
 	&cpu_psci_ops,
 	NULL,
 };
+static unsigned char cpu_ops_indexes[NR_CPUS] __ro_after_init;
 
-static const struct cpu_operations * __init cpu_get_ops(const char *name)
+static unsigned char __init get_cpu_ops_index(const char *name)
 {
-	const struct cpu_operations *const *ops;
-
-	ops = acpi_disabled ? dt_supported_cpu_ops : acpi_supported_cpu_ops;
+	const struct cpu_operations *const *ops = cpu_ops;
+	unsigned char index = 0;
 
 	while (*ops) {
 		if (!strcmp(name, (*ops)->name))
-			return *ops;
+			return (index + 1);
 
 		ops++;
+		index++;
 	}
 
-	return NULL;
+	return 0;
 }
 
-static const char *__init cpu_read_enable_method(int cpu)
+static const char *__init get_cpu_method(int cpu)
 {
 	const char *enable_method;
 
@@ -98,21 +92,33 @@ static const char *__init cpu_read_enable_method(int cpu)
  */
 int __init init_cpu_ops(int cpu)
 {
-	const char *enable_method = cpu_read_enable_method(cpu);
+	const char *enable_method = get_cpu_method(cpu);
+	unsigned char index;
 
 	if (!enable_method)
 		return -ENODEV;
 
-	cpu_ops[cpu] = cpu_get_ops(enable_method);
-	if (!cpu_ops[cpu]) {
+	index = get_cpu_ops_index(enable_method);
+	if (!index) {
 		pr_warn("Unsupported enable-method: %s\n", enable_method);
 		return -EOPNOTSUPP;
 	}
 
+	cpu_ops_indexes[cpu] = index;
+
 	return 0;
 }
 
 const struct cpu_operations *get_cpu_ops(int cpu)
 {
-	return cpu_ops[cpu];
+	unsigned char index = cpu_ops_indexes[cpu];
+
+	/*
+	 * The corresponding CPU operation isn't set when the
+	 * index is equal to zero.
+	 */
+	if (!index)
+		return NULL;
+
+	return cpu_ops[index - 1];
 }
-- 
2.23.0


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