ACPI: processor: perflib: Fix initial _PPC limit application

JIRA: https://issues.redhat.com/browse/RHEL-114091

commit d33bd88
Author: Jiayi Li <lijiayi@kylinos.cn>
Date: Mon, 21 Jul 2025 15:21:48 +0000

If the BIOS sets a _PPC frequency limit upfront, it will fail to take
effect due to a call ordering issue.  Namely, freq_qos_update_request()
is called before freq_qos_add_request() for the given request causing
the constraint update to be ignored.  The call sequence in question is
as follows:

cpufreq_policy_online()
  acpi_cpufreq_cpu_init()
    acpi_processor_register_performance()
      acpi_processor_get_performance_info()
        acpi_processor_get_platform_limit()
         freq_qos_update_request(&perflib_req) <- inactive QoS request
  blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
                               CPUFREQ_CREATE_POLICY)
    acpi_processor_notifier()
      acpi_processor_ppc_init()
        freq_qos_add_request(&perflib_req) <- QoS request activation

Address this by adding an acpi_processor_get_platform_limit() call
to acpi_processor_ppc_init(), after the perflib_req activation via
freq_qos_add_request(), which causes the initial _PPC limit to be
picked up as appropriate.  However, also ensure that the _PPC limit
will not be picked up in the cases when the cpufreq driver does not
call acpi_processor_register_performance() by adding a pr->performance
check to the related_cpus loop in acpi_processor_ppc_init().

Fixes: d15ce41 ("ACPI: cpufreq: Switch to QoS requests instead of cpufreq notifier")
Signed-off-by: Jiayi Li <lijiayi@kylinos.cn>
Link: https://patch.msgid.link/20250721032606.3459369-1-lijiayi@kylinos.cn
[ rjw: Consolidate pr-related checks in acpi_processor_ppc_init() ]
[ rjw: Subject and changelog adjustments ]
Cc: 5.4+ <stable@vger.kernel.org> # 5.4+: 2d8b39a ACPI: processor: Avoid NULL pointer dereferences at init time
Cc: 5.4+ <stable@vger.kernel.org> # 5.4+: 3000ce3 cpufreq: Use per-policy frequency QoS
Cc: 5.4+ <stable@vger.kernel.org> # 5.4+: a1bb46c ACPI: processor: Add QoS requests for all CPUs
Cc: 5.4+ <stable@vger.kernel.org> # 5.4+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Mark Langsdorf <mlangsdo@redhat.com>

Author: mlangsdorf

drivers/acpi/processor_perflib.c

@@ -172,11 +172,14 @@ void acpi_processor_ppc_init(struct cpufreq_policy *policy)
 {
 	unsigned int cpu;
 
+	if (ignore_ppc == 1)
+		return;
+
 	for_each_cpu(cpu, policy->related_cpus) {
 		struct acpi_processor *pr = per_cpu(processors, cpu);
 		int ret;
 
-		if (!pr)
+		if (!pr || !pr->performance)
 			continue;
 
 		/*
@@ -192,6 +195,11 @@ void acpi_processor_ppc_init(struct cpufreq_policy *policy)
 		if (ret < 0)
 			pr_err("Failed to add freq constraint for CPU%d (%d)\n",
 			       cpu, ret);
+
+		ret = acpi_processor_get_platform_limit(pr);
+		if (ret)
+			pr_err("Failed to update freq constraint for CPU%d (%d)\n",
+			       cpu, ret);
 	}
 }