PM: EM: Add function for registering a PD without capacity update

JIRA: https://issues.redhat.com/browse/RHEL-112493

commit e042354
Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Date:   Fri Sep 5 15:44:45 2025 +0200

    PM: EM: Add function for registering a PD without capacity update

    The intel_pstate driver manages CPU capacity changes itself and it does
    not need an update of the capacity of all CPUs in the system to be
    carried out after registering a PD.

    Moreover, in some configurations (for instance, an SMT-capable
    hybrid x86 system booted with nosmt in the kernel command line) the
    em_check_capacity_update() call at the end of em_dev_register_perf_domain()
    always fails and reschedules itself to run once again in 1 s, so
    effectively it runs in vain every 1 s forever.

    To address this, introduce a new variant of em_dev_register_perf_domain(),
    called em_dev_register_pd_no_update(), that does not invoke
    em_check_capacity_update(), and make intel_pstate use it instead of the
    original.

    Fixes: 7b010f9 ("cpufreq: intel_pstate: EAS support for hybrid platforms")
    Closes: https://lore.kernel.org/linux-pm/40212796-734c-4140-8a85-854f72b8144d@panix.com/
    Reported-by: Kenneth R. Crudup <kenny@panix.com>
    Tested-by: Kenneth R. Crudup <kenny@panix.com>
    Cc: 6.16+ <stable@vger.kernel.org> # 6.16+
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Signed-off-by: David Arcari <darcari@redhat.com>

Author: darcari

drivers/cpufreq/intel_pstate.c

@@ -1035,8 +1035,8 @@ static bool hybrid_register_perf_domain(unsigned int cpu)
 	if (!cpu_dev)
 		return false;
 
-	if (em_dev_register_perf_domain(cpu_dev, HYBRID_EM_STATE_COUNT, &cb,
-					cpumask_of(cpu), false))
+	if (em_dev_register_pd_no_update(cpu_dev, HYBRID_EM_STATE_COUNT, &cb,
+					 cpumask_of(cpu), false))
 		return false;
 
 	cpudata->pd_registered = true;

include/linux/energy_model.h

@@ -171,6 +171,9 @@ int em_dev_update_perf_domain(struct device *dev,
 int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
 				const struct em_data_callback *cb,
 				const cpumask_t *cpus, bool microwatts);
+int em_dev_register_pd_no_update(struct device *dev, unsigned int nr_states,
+				 const struct em_data_callback *cb,
+				 const cpumask_t *cpus, bool microwatts);
 void em_dev_unregister_perf_domain(struct device *dev);
 struct em_perf_table *em_table_alloc(struct em_perf_domain *pd);
 void em_table_free(struct em_perf_table *table);
@@ -351,6 +354,13 @@ int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
 {
 	return -EINVAL;
 }
+static inline
+int em_dev_register_pd_no_update(struct device *dev, unsigned int nr_states,
+				 const struct em_data_callback *cb,
+				 const cpumask_t *cpus, bool microwatts)
+{
+	return -EINVAL;
+}
 static inline void em_dev_unregister_perf_domain(struct device *dev)
 {
 }

kernel/power/energy_model.c

@@ -619,6 +619,30 @@ EXPORT_SYMBOL_GPL(em_cpu_get);
 int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
 				const struct em_data_callback *cb,
 				const cpumask_t *cpus, bool microwatts)
+{
+	int ret = em_dev_register_pd_no_update(dev, nr_states, cb, cpus, microwatts);
+
+	if (_is_cpu_device(dev))
+		em_check_capacity_update();
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(em_dev_register_perf_domain);
+
+/**
+ * em_dev_register_pd_no_update() - Register a perf domain for a device
+ * @dev : Device to register the PD for
+ * @nr_states : Number of performance states in the new PD
+ * @cb : Callback functions for populating the energy model
+ * @cpus : CPUs to include in the new PD (mandatory if @dev is a CPU device)
+ * @microwatts : Whether or not the power values in the EM will be in uW
+ *
+ * Like em_dev_register_perf_domain(), but does not trigger a CPU capacity
+ * update after registering the PD, even if @dev is a CPU device.
+ */
+int em_dev_register_pd_no_update(struct device *dev, unsigned int nr_states,
+				 const struct em_data_callback *cb,
+				 const cpumask_t *cpus, bool microwatts)
 {
 	struct em_perf_table *em_table;
 	unsigned long cap, prev_cap = 0;
@@ -703,12 +727,9 @@ int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
 unlock:
 	mutex_unlock(&em_pd_mutex);
 
-	if (_is_cpu_device(dev))
-		em_check_capacity_update();
-
 	return ret;
 }
-EXPORT_SYMBOL_GPL(em_dev_register_perf_domain);
+EXPORT_SYMBOL_GPL(em_dev_register_pd_no_update);
 
 /**
  * em_dev_unregister_perf_domain() - Unregister Energy Model (EM) for a device