linux-kernel - Re: [PATCH 13/13] cpufreq: make sure frequency transitions are serialized

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Date:	Mon, 24 Jun 2013 18:38:17 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <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,
	dave.martin@....com
Subject: Re: [PATCH 13/13] cpufreq: make sure frequency transitions are serialized

On 24 June 2013 17:13, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Wednesday, June 19, 2013 02:23:07 PM Viresh Kumar wrote:
>>       case CPUFREQ_POSTCHANGE:
>> +             WARN_ON(!transition_ongoing--);
>
> Shouldn't we try to avoid going into the negative range here?

What about this patch? Find it attached to apply.

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 2d53f47..6624694 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -107,6 +107,9 @@ static void handle_update(struct work_struct *work);
 static BLOCKING_NOTIFIER_HEAD(cpufreq_policy_notifier_list);
 static struct srcu_notifier_head cpufreq_transition_notifier_list;

+/* Tracks status of transition */
+static int transition_ongoing;
+
 static bool init_cpufreq_transition_notifier_list_called;
 static int __init init_cpufreq_transition_notifier_list(void)
 {
@@ -264,6 +267,13 @@ void __cpufreq_notify_transition(struct
cpufreq_policy *policy,
        switch (state) {

        case CPUFREQ_PRECHANGE:
+               if (transition_ongoing) {
+                       WARN(1, "In middle of another frequency transition\n");
+                       return;
+               }
+
+               transition_ongoing++;
+
                /* detect if the driver reported a value as "old frequency"
                 * which is not equal to what the cpufreq core thinks is
                 * "old frequency".
@@ -283,6 +293,13 @@ void __cpufreq_notify_transition(struct
cpufreq_policy *policy,
                break;

        case CPUFREQ_POSTCHANGE:
+               if (!transition_ongoing) {
+                       WARN(1, "No frequency transition in progress\n");
+                       return;
+               }
+
+               transition_ongoing--;
+
                adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
                pr_debug("FREQ: %lu - CPU: %lu", (unsigned long)freqs->new,
                        (unsigned long)freqs->cpu);
@@ -1458,6 +1475,8 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy,

        if (cpufreq_disabled())
                return -ENODEV;
+       if (transition_ongoing)
+               return -EBUSY;

        /* Make sure that target_freq is within supported range */
        if (target_freq > policy->max)

Download attachment "0001-cpufreq-make-sure-frequency-transitions-are-serializ.patch" of type "application/octet-stream" (2571 bytes)