ACPI: processor: perflib: Fix initial _PPC limit application

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: d15ce412737a ("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+: 2d8b39a62a5d ACPI: processor: Avoid NULL pointer dereferences at init time
Cc: 5.4+ <stable@vger.kernel.org> # 5.4+: 3000ce3c52f8 cpufreq: Use per-policy frequency QoS
Cc: 5.4+ <stable@vger.kernel.org> # 5.4+: a1bb46c36ce3 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>

diff --git a/drivers/acpi/processor_perflib.c b/drivers/acpi/processor_perflib.c
index 64b8d1e1959431f43d338095836ecf0b578ba0c2..755003bf3a458b6c8890011a1180c3ee6458d388 100644 (file)
--- a/drivers/acpi/processor_perflib.c
+++ b/drivers/acpi/processor_perflib.c
@@ -173,11 +173,14 @@ 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;
 
                /*
@@ -193,6 +196,11 @@ 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);
        }
 }