lib/acpi: Fix the behavior to fit with how it used to be

z_acpi_get_cpu() used to retrieve the local apic on enabled CPU, where
n was about the n'th enabled CPU, not just the n'th local apic.
The system indeed keeps local apic info also about non-enabled CPU,
and we don't care about these as there is nothing to do about it.

This issue exists on up_squared board for instance, but it's a common
one anyway.

Signed-off-by: Tomasz Bursztyka <[email protected]>
(cherry picked from commit c294b7d)

include/zephyr/acpi/acpi.h

@@ -175,10 +175,10 @@ int acpi_drhd_get(enum AcpiDmarScopeType scope, struct acpi_dmar_device_scope *d
 	union acpi_dmar_id *dmar_id, int *num_inst, int max_inst);
 
 /**
- * @brief Retrieve lapic info for a specific cpu.
+ * @brief Retrieve the 'n'th enabled local apic info.
  *
  * @param cpu_num the cpu number
- * @return lapic info on success or NULL
+ * @return local apic info on success or NULL otherwise
  */
-struct acpi_madt_local_apic *acpi_local_apic_get(uint32_t cpu_num);
+struct acpi_madt_local_apic *acpi_local_apic_get(int cpu_num);
 #endif

lib/acpi/acpi.c

@@ -791,21 +791,29 @@ int acpi_drhd_get(enum AcpiDmarScopeType scope, struct acpi_dmar_device_scope *d
 	return 0;
 }
 
-struct acpi_madt_local_apic *acpi_local_apic_get(uint32_t cpu_num)
+#define ACPI_CPU_FLAGS_ENABLED 0x01u
+
+struct acpi_madt_local_apic *acpi_local_apic_get(int cpu_num)
 {
 	struct acpi_madt_local_apic *lapic;
 	int cpu_cnt;
+	int idx;
 
 	if (acpi_madt_entry_get(ACPI_MADT_TYPE_LOCAL_APIC, (ACPI_SUBTABLE_HEADER **)&lapic,
 				&cpu_cnt)) {
 		/* Error on MAD table. */
 		return NULL;
 	}
 
-	if ((cpu_num >= cpu_cnt) || !(lapic[cpu_num].LapicFlags & 1u)) {
-		/* Proccessor not enabled. */
-		return NULL;
+	for (idx = 0; cpu_num >= 0 && idx < cpu_cnt; idx++) {
+		if (lapic[idx].LapicFlags & ACPI_CPU_FLAGS_ENABLED) {
+			if (cpu_num == 0) {
+				return &lapic[idx];
+			}
+
+			cpu_num--;
+		}
 	}
 
-	return &lapic[cpu_num];
+	return NULL;
 }