linux-kernel - [RFC V2 1/6] cpufreq: Replace "max_transition_latency" with "dynamic

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Date:   Thu, 13 Jul 2017 11:10:52 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Rafael Wysocki <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux@...inikbrodowski.net, linux-kernel@...r.kernel.org
Subject: [RFC V2 1/6] cpufreq: Replace "max_transition_latency" with "dynamic_switching"

There is no limitation in the ondemand or conservative governors which
disallow the transition_latency to be greater than 10 ms.

The max_transition_latency field is rather used to disallow automatic
dynamic frequency switching for platforms which didn't wanted these
governors to run.

Replace max_transition_latency with a boolean (dynamic_switching) and
check for transition_latency == CPUFREQ_ETERNAL along with that. This
makes it pretty straight forward to read/understand now.

Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 drivers/cpufreq/cpufreq.c          | 8 ++++----
 drivers/cpufreq/cpufreq_governor.h | 2 +-
 include/linux/cpufreq.h            | 9 ++-------
 3 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 9bf97a366029..dcef293c5e2c 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1988,13 +1988,13 @@ static int cpufreq_init_governor(struct cpufreq_policy *policy)
 	if (!policy->governor)
 		return -EINVAL;
 
-	if (policy->governor->max_transition_latency &&
-	    policy->cpuinfo.transition_latency >
-	    policy->governor->max_transition_latency) {
+	/* Platform doesn't want dynamic frequency switching ? */
+	if (policy->governor->dynamic_switching &&
+	    policy->cpuinfo.transition_latency == CPUFREQ_ETERNAL) {
 		struct cpufreq_governor *gov = cpufreq_fallback_governor();
 
 		if (gov) {
-			pr_warn("%s governor failed, too long transition latency of HW, fallback to %s governor\n",
+			pr_warn("Transition latency set to CPUFREQ_ETERNAL, can't use %s governor. Fallback to %s governor\n",
 				policy->governor->name, gov->name);
 			policy->governor = gov;
 		} else {
diff --git a/drivers/cpufreq/cpufreq_governor.h b/drivers/cpufreq/cpufreq_governor.h
index 0236ec2cd654..7b7839c45fba 100644
--- a/drivers/cpufreq/cpufreq_governor.h
+++ b/drivers/cpufreq/cpufreq_governor.h
@@ -160,7 +160,7 @@ void cpufreq_dbs_governor_limits(struct cpufreq_policy *policy);
 #define CPUFREQ_DBS_GOVERNOR_INITIALIZER(_name_)			\
 	{								\
 		.name = _name_,						\
-		.max_transition_latency	= TRANSITION_LATENCY_LIMIT,	\
+		.dynamic_switching = true,				\
 		.owner = THIS_MODULE,					\
 		.init = cpufreq_dbs_governor_init,			\
 		.exit = cpufreq_dbs_governor_exit,			\
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 905117bd5012..3d8c52b3b5df 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -487,14 +487,10 @@ static inline unsigned long cpufreq_scale(unsigned long old, u_int div,
  * polling frequency is 1000 times the transition latency of the processor. The
  * ondemand governor will work on any processor with transition latency <= 10ms,
  * using appropriate sampling rate.
- *
- * For CPUs with transition latency > 10ms (mostly drivers with CPUFREQ_ETERNAL)
- * the ondemand governor will not work. All times here are in us (microseconds).
  */
 #define MIN_SAMPLING_RATE_RATIO		(2)
 #define LATENCY_MULTIPLIER		(1000)
 #define MIN_LATENCY_MULTIPLIER		(20)
-#define TRANSITION_LATENCY_LIMIT	(10 * 1000 * 1000)
 
 struct cpufreq_governor {
 	char	name[CPUFREQ_NAME_LEN];
@@ -507,9 +503,8 @@ struct cpufreq_governor {
 					 char *buf);
 	int	(*store_setspeed)	(struct cpufreq_policy *policy,
 					 unsigned int freq);
-	unsigned int max_transition_latency; /* HW must be able to switch to
-			next freq faster than this value in nano secs or we
-			will fallback to performance governor */
+	/* For governors which change frequency dynamically by themselves */
+	bool			dynamic_switching;
 	struct list_head	governor_list;
 	struct module		*owner;
 };
-- 
2.13.0.71.gd7076ec9c9cb