ACPI: processor: perflib: Avoid updating frequency QoS unnecessarily

Modify acpi_processor_get_platform_limit() to avoid updating its
frequency QoS request when the _PPC return value has not changed
by comparing that value to the previous _PPC return value stored in
the performance_platform_limit field of the struct acpi_processor
corresponding to the given CPU.

While at it, do the _PPC return value check against the state count
earlier, to avoid setting performance_platform_limit to an invalid
value, and make acpi_processor_ppc_init() use FREQ_QOS_MAX_DEFAULT_VALUE
as the "no limit" frequency QoS for consistency.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/processor_perflib.c

@@ -76,13 +76,16 @@ static int acpi_processor_get_platform_limit(struct acpi_processor *pr)
 
 	index = ppc;
 
+	if (pr->performance_platform_limit == index ||
+	    ppc >= pr->performance->state_count)
+		return 0;
+
 	pr_debug("CPU %d: _PPC is %d - frequency %s limited\n", pr->id,
 		 index, index ? "is" : "is not");
 
 	pr->performance_platform_limit = index;
 
-	if (ppc >= pr->performance->state_count ||
-	    unlikely(!freq_qos_request_active(&pr->perflib_req)))
+	if (unlikely(!freq_qos_request_active(&pr->perflib_req)))
 		return 0;
 
 	/*
@@ -178,9 +181,16 @@ void acpi_processor_ppc_init(struct cpufreq_policy *policy)
 		if (!pr)
 			continue;
 
+		/*
+		 * Reset performance_platform_limit in case there is a stale
+		 * value in it, so as to make it match the "no limit" QoS value
+		 * below.
+		 */
+		pr->performance_platform_limit = 0;
+
 		ret = freq_qos_add_request(&policy->constraints,
-					   &pr->perflib_req,
-					   FREQ_QOS_MAX, INT_MAX);
+					   &pr->perflib_req, FREQ_QOS_MAX,
+					   FREQ_QOS_MAX_DEFAULT_VALUE);
 		if (ret < 0)
 			pr_err("Failed to add freq constraint for CPU%d (%d)\n",
 			       cpu, ret);