linux-kernel - [PATCH V5 2/2] cpufreq: Process remote callbacks from any CPU if the platform permits

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Message-Id: <c121a20eff05565155852c070e83504bf117da3e.1501223897.git.viresh.kumar@linaro.org>
Date:   Fri, 28 Jul 2017 12:16:39 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Rafael Wysocki <rjw@...ysocki.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        smuckle.linux@...il.com, juri.lelli@....com,
        Morten.Rasmussen@....com, patrick.bellasi@....com,
        eas-dev@...ts.linaro.org, skannan@...eaurora.org,
        joelaf@...gle.com, linux-kernel@...r.kernel.org
Subject: [PATCH V5 2/2] 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@...aro.org>
---
 drivers/cpufreq/cpufreq-dt.c |  1 +
 include/linux/cpufreq.h      | 18 ++++++++++++++++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c
index fef3c2160691..d83ab94d041a 100644
--- a/drivers/cpufreq/cpufreq-dt.c
+++ b/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;
 
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index b3b6e8203e82..227cd0f13300 100644
--- a/include/linux/cpufreq.h
+++ b/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;
-- 
2.13.0.71.gd7076ec9c9cb