linux-kernel - [PATCH] cpufreq: Fix serialization of frequency transitions

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Message-Id: <d367fc6fda0f167678a83e1d70e0cfd240a32cbc.1372759022.git.viresh.kumar@linaro.org>
Date:	Tue,  2 Jul 2013 16:36:28 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	rjw@...k.pl
Cc:	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, robin.randhawa@....com,
	Steve.Bannister@....com, Liviu.Dudau@....com,
	charles.garcia-tobin@....com, arvind.chauhan@....com,
	broonie@...aro.org, Viresh Kumar <viresh.kumar@...aro.org>
Subject: [PATCH] cpufreq: Fix serialization of frequency transitions

Commit 7c30ed ("cpufreq: make sure frequency transitions are serialized")
interacts poorly with systems that have a single core freqency for all
cores.  On such systems we have a single policy for all cores with
several CPUs.  When we do a frequency transition the governor calls the
pre and post change notifiers which causes cpufreq_notify_transition()
per CPU.  Since the policy is the same for all of them all CPUs after
the first and the warnings added are generated by checking a per-policy
flag the warnings will be triggered for all cores after the first.

Fix this by allowing notifier to be called for n times. Where n is the number of
cpus in policy->cpus.

Reported-and-Tested-by: Mark Brown <broonie@...aro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
Hi Rafael,

This is a fix for 3.11.

 drivers/cpufreq/cpufreq.c | 7 ++++---
 include/linux/cpufreq.h   | 2 +-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index b557503..b7bda8d 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -312,11 +312,12 @@ static void __cpufreq_notify_transition(struct cpufreq_policy *policy,
 	switch (state) {
 
 	case CPUFREQ_PRECHANGE:
-		if (WARN(policy->transition_ongoing,
+		if (WARN(policy->transition_ongoing ==
+					cpumask_weight(policy->cpus),
 				"In middle of another frequency transition\n"))
 			return;
 
-		policy->transition_ongoing = true;
+		policy->transition_ongoing++;
 
 		/* detect if the driver reported a value as "old frequency"
 		 * which is not equal to what the cpufreq core thinks is
@@ -341,7 +342,7 @@ static void __cpufreq_notify_transition(struct cpufreq_policy *policy,
 				"No frequency transition in progress\n"))
 			return;
 
-		policy->transition_ongoing = false;
+		policy->transition_ongoing--;
 
 		adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
 		pr_debug("FREQ: %lu - CPU: %lu", (unsigned long)freqs->new,
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 4d7390b..90d5a15 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -119,7 +119,7 @@ struct cpufreq_policy {
 
 	struct kobject		kobj;
 	struct completion	kobj_unregister;
-	bool			transition_ongoing; /* Tracks transition status */
+	int			transition_ongoing; /* Tracks transition status */
 };
 
 #define CPUFREQ_ADJUST			(0)
-- 
1.7.12.rc2.18.g61b472e

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