cpufreq: Process remote callbacks from any CPU if the platform permits

On many platforms, CPUs can do DVFS across cpufreq policies. i.e CPU
from policy-A can change frequency of CPUs belonging to policy-B.

This is quite common in case of ARM platforms where we don't
configure any per-cpu register.

Add a flag to identify such platforms and update
cpufreq_can_do_remote_dvfs() to allow remote callbacks if this flag is
set.

Also enable the flag for cpufreq-dt driver which is used only on ARM
platforms currently.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Saravana Kannan <skannan@codeaurora.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/cpufreq-dt.c

@@ -274,6 +274,7 @@ static int cpufreq_init(struct cpufreq_policy *policy)
 		transition_latency = CPUFREQ_ETERNAL;
 
 	policy->cpuinfo.transition_latency = transition_latency;
+	policy->dvfs_possible_from_any_cpu = true;
 
 	return 0;
 

include/linux/cpufreq.h

@@ -127,6 +127,15 @@ struct cpufreq_policy {
 	 */
 	unsigned int		transition_delay_us;
 
+	/*
+	 * Remote DVFS flag (Not added to the driver structure as we don't want
+	 * to access another structure from scheduler hotpath).
+	 *
+	 * Should be set if CPUs can do DVFS on behalf of other CPUs from
+	 * different cpufreq policies.
+	 */
+	bool			dvfs_possible_from_any_cpu;
+
 	 /* Cached frequency lookup from cpufreq_driver_resolve_freq. */
 	unsigned int cached_target_freq;
 	int cached_resolved_idx;
@@ -564,8 +573,13 @@ struct governor_attr {
 
 static inline bool cpufreq_can_do_remote_dvfs(struct cpufreq_policy *policy)
 {
-	/* Allow remote callbacks only on the CPUs sharing cpufreq policy */
-	if (cpumask_test_cpu(smp_processor_id(), policy->cpus))
+	/*
+	 * Allow remote callbacks if:
+	 * - dvfs_possible_from_any_cpu flag is set
+	 * - the local and remote CPUs share cpufreq policy
+	 */
+	if (policy->dvfs_possible_from_any_cpu ||
+	    cpumask_test_cpu(smp_processor_id(), policy->cpus))
 		return true;
 
 	return false;