diff --git a/drivers/xen/xen-acpi-pad.c b/drivers/xen/xen-acpi-pad.c
index 40c4bc0..f83b754 100644
--- a/drivers/xen/xen-acpi-pad.c
+++ b/drivers/xen/xen-acpi-pad.c
@@ -77,27 +77,14 @@
 	return num;
 }
 
-/* Notify firmware how many CPUs are idle */
-static void acpi_pad_ost(acpi_handle handle, int stat,
-	uint32_t idle_nums)
-{
-	union acpi_object params[3] = {
-		{.type = ACPI_TYPE_INTEGER,},
-		{.type = ACPI_TYPE_INTEGER,},
-		{.type = ACPI_TYPE_BUFFER,},
-	};
-	struct acpi_object_list arg_list = {3, params};
-
-	params[0].integer.value = ACPI_PROCESSOR_AGGREGATOR_NOTIFY;
-	params[1].integer.value =  stat;
-	params[2].buffer.length = 4;
-	params[2].buffer.pointer = (void *)&idle_nums;
-	acpi_evaluate_object(handle, "_OST", &arg_list, NULL);
-}
-
 static void acpi_pad_handle_notify(acpi_handle handle)
 {
 	int idle_nums;
+	struct acpi_buffer param = {
+		.length = 4,
+		.pointer = (void *)&idle_nums,
+	};
+
 
 	mutex_lock(&xen_cpu_lock);
 	idle_nums = acpi_pad_pur(handle);
@@ -109,7 +96,8 @@
 	idle_nums = xen_acpi_pad_idle_cpus(idle_nums)
 		    ?: xen_acpi_pad_idle_cpus_num();
 	if (idle_nums >= 0)
-		acpi_pad_ost(handle, 0, idle_nums);
+		acpi_evaluate_ost(handle, ACPI_PROCESSOR_AGGREGATOR_NOTIFY,
+				  0, &param);
 	mutex_unlock(&xen_cpu_lock);
 }