[RFC][PATCH v0.1 4/6] PM: EM: Introduce em_dev_expand_perf_domain()

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Introduce a helper function for adding a CPU to an existing EM perf
domain.

Subsequently, this will be used by the intel_pstate driver to add new
CPUs to existing perf domains when those CPUs go online for the first
time after the initialization of the driver.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 include/linux/energy_model.h |    5 +++++
 kernel/power/energy_model.c  |   32 ++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

Index: linux-pm/kernel/power/energy_model.c
===================================================================
--- linux-pm.orig/kernel/power/energy_model.c
+++ linux-pm/kernel/power/energy_model.c
@@ -696,6 +696,38 @@ void em_dev_unregister_perf_domain(struc
 }
 EXPORT_SYMBOL_GPL(em_dev_unregister_perf_domain);
 
+/**
+ * em_dev_expand_perf_domain() - Expand CPU perf domain
+ * @dev: CPU device of a CPU in the perf domain.
+ * @new_cpu: CPU to add to the perf domain.
+ */
+int em_dev_expand_perf_domain(struct device *dev, int new_cpu)
+{
+	struct device *new_cpu_dev;
+	struct em_perf_domain *pd;
+
+	if (IS_ERR_OR_NULL(dev) || !_is_cpu_device(dev))
+		return -EINVAL;
+
+	new_cpu_dev = get_cpu_device(new_cpu);
+	if (!new_cpu_dev)
+		return -EINVAL;
+
+	guard(mutex)(&em_pd_mutex);
+
+	if (em_pd_get(new_cpu_dev))
+		return -EEXIST;
+
+	pd = em_pd_get(dev);
+	if (!pd)
+		return -EINVAL;
+
+	cpumask_set_cpu(new_cpu, em_span_cpus(pd));
+	new_cpu_dev->em_pd = pd;
+
+	return 0;
+}
+
 static struct em_perf_table __rcu *em_table_dup(struct em_perf_domain *pd)
 {
 	struct em_perf_table __rcu *em_table;
Index: linux-pm/include/linux/energy_model.h
===================================================================
--- linux-pm.orig/include/linux/energy_model.h
+++ linux-pm/include/linux/energy_model.h
@@ -172,6 +172,7 @@ int em_dev_register_perf_domain(struct d
 				struct em_data_callback *cb, cpumask_t *span,
 				bool microwatts);
 void em_dev_unregister_perf_domain(struct device *dev);
+int em_dev_expand_perf_domain(struct device *dev, int new_cpu);
 struct em_perf_table __rcu *em_table_alloc(struct em_perf_domain *pd);
 void em_table_free(struct em_perf_table __rcu *table);
 int em_dev_compute_costs(struct device *dev, struct em_perf_state *table,
@@ -354,6 +355,10 @@ int em_dev_register_perf_domain(struct d
 static inline void em_dev_unregister_perf_domain(struct device *dev)
 {
 }
+static inline int em_dev_expand_perf_domain(struct device *dev, int new_cpu)
+{
+	return -EINVAL;
+}
 static inline struct em_perf_domain *em_cpu_get(int cpu)
 {
 	return NULL;