linux-kernel - [PATCH 1/2] cpufreq: Allow light-weight tear down on CPU offline operation

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Date:   Mon, 11 Feb 2019 14:11:35 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Rafael Wysocki <rjw@...ysocki.net>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] cpufreq: Allow light-weight tear down on CPU offline operation

The cpufreq core doesn't remove the cpufreq policy anymore on CPU
offline operation, rather that happens when the CPU device gets
unregistered from the kernel. This allows faster recovery when the CPU
comes back online. This is also very useful during system wide
suspend/resume where we offline all non-boot CPUs during suspend and
then bring them back on resume.

This commit takes the same idea a step ahead to allow drivers to do
light weight tear-down during CPU offline operation.

A new callback is introduced, light_weight_exit(), which gets called
when all the CPUs of a policy are removed/offlined and the existing
exit() callback gets called when the policy gets freed.

Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 drivers/cpufreq/cpufreq.c | 16 +++++++++++-----
 include/linux/cpufreq.h   |  1 +
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 96a69c67a545..215a8bfc78bb 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1421,11 +1421,12 @@ static int cpufreq_offline(unsigned int cpu)
 		cpufreq_exit_governor(policy);
 
 	/*
-	 * Perform the ->exit() even during light-weight tear-down,
-	 * since this is a core component, and is essential for the
-	 * subsequent light-weight ->init() to succeed.
+	 * Perform the ->light_weight_exit() during light-weight tear-down, as
+	 * that allows fast recovery when the CPU comes back.
 	 */
-	if (cpufreq_driver->exit) {
+	if (cpufreq_driver->light_weight_exit) {
+		cpufreq_driver->light_weight_exit(policy);
+	} else if (cpufreq_driver->exit) {
 		cpufreq_driver->exit(policy);
 		policy->freq_table = NULL;
 	}
@@ -1454,8 +1455,13 @@ static void cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif)
 	cpumask_clear_cpu(cpu, policy->real_cpus);
 	remove_cpu_dev_symlink(policy, dev);
 
-	if (cpumask_empty(policy->real_cpus))
+	if (cpumask_empty(policy->real_cpus)) {
+		/* We did light-weight exit earlier, do full tear down now */
+		if (cpufreq_driver->light_weight_exit)
+			cpufreq_driver->exit(policy);
+
 		cpufreq_policy_free(policy);
+	}
 }
 
 /**
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 9db074ecbbd7..36ce31516041 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -325,6 +325,7 @@ struct cpufreq_driver {
 	/* optional */
 	int		(*bios_limit)(int cpu, unsigned int *limit);
 
+	int		(*light_weight_exit)(struct cpufreq_policy *policy);
 	int		(*exit)(struct cpufreq_policy *policy);
 	void		(*stop_cpu)(struct cpufreq_policy *policy);
 	int		(*suspend)(struct cpufreq_policy *policy);
-- 
2.20.1.321.g9e740568ce00