Date:	Fri, 15 Nov 2013 15:42:29 +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, tianyu.lan@...el.com, nm@...com,
	jinchoi@...adcom.com, sebastian.capella@...aro.org,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: [PATCH] cpufreq: suspend/resume governors with PM notifiers

This patch adds PM notifiers for handling suspend/resume of cpufreq governors.
This is required for early suspend and late resume of governors.

There are multiple reasons that support this patch:
- Firstly it looks very much logical to stop governors when we know we are going
  into suspend. But the question is when? Is PM notifiers the right place?
  Following reasons are the supporting hands for this decision.
- Nishanth Menon (TI) found an interesting problem on his platform, OMAP. His board
  wasn't working well with suspend/resume as calls for removing non-boot CPUs
  was turning out into a call to drivers ->target() which then tries to play
  with regulators. But regulators and their I2C bus were already suspended and
  this resulted in a failure. This is why we need a PM notifier here.
- Lan Tianyu (Intel) & Jinhyuk Choi (Broadcom) found another issue where
  tunables configuration for clusters/sockets with non-boot CPUs was getting
  lost after suspend/resume, as we were notifying governors with
  CPUFREQ_GOV_POLICY_EXIT on removal of the last cpu for that policy and so
  deallocating memory for tunables.

All above problems get fixed with having a PM notifier in place which will stop
any operation on governor. Hence no need to do any special handling of variables
like (frozen) in suspend/resume paths.

Reported-by: Lan Tianyu <tianyu.lan@...el.com>
Reported-by: Nishanth Menon <nm@...com>
Reported-by: Jinhyuk Choi <jinchoi@...adcom.com>
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---

Hi Guys,

Can you please verify if this fixes issues reported by you? I have tested this
for multiple suspend-resumes on my thinkpad. It doesn't crash :)

 drivers/cpufreq/cpufreq.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 02d534d..c87ced9 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -26,6 +26,7 @@
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
+#include <linux/suspend.h>
 #include <linux/syscore_ops.h>
 #include <linux/tick.h>
 #include <trace/events/power.h>
@@ -47,6 +48,9 @@ static LIST_HEAD(cpufreq_policy_list);
 static DEFINE_PER_CPU(char[CPUFREQ_NAME_LEN], cpufreq_cpu_governor);
 #endif
 
+/* Flag to suspend/resume CPUFreq governors */
+static bool cpufreq_suspended;
+
 static inline bool has_target(void)
 {
 	return cpufreq_driver->target_index || cpufreq_driver->target;
@@ -1462,6 +1466,54 @@ static struct subsys_interface cpufreq_interface = {
 	.remove_dev	= cpufreq_remove_dev,
 };
 
+/*
+ * PM Notifier for suspending governors as some platforms can't change frequency
+ * after this point in suspend cycle. Because some of the devices (like: i2c,
+ * regulators, etc) they use for changing frequency are suspended quickly after
+ * this point.
+ */
+static int cpufreq_pm_notify(struct notifier_block *nb, unsigned long action,
+		void *data)
+{
+	struct cpufreq_policy *policy;
+	unsigned long flags;
+
+	if (!has_target())
+		return NOTIFY_OK;
+
+	if (action == PM_SUSPEND_PREPARE) {
+		pr_debug("%s: Suspending Governors\n", __func__);
+
+		list_for_each_entry(policy, &cpufreq_policy_list, policy_list)
+			if (__cpufreq_governor(policy, CPUFREQ_GOV_STOP))
+				pr_err("%s: Failed to stop governor for policy: %p\n",
+						__func__, policy);
+
+		write_lock_irqsave(&cpufreq_driver_lock, flags);
+		cpufreq_suspended = true;
+		write_unlock_irqrestore(&cpufreq_driver_lock, flags);
+	} else if (action == PM_POST_SUSPEND) {
+		pr_debug("%s: Resuming Governors\n", __func__);
+
+		write_lock_irqsave(&cpufreq_driver_lock, flags);
+		cpufreq_suspended = false;
+		write_unlock_irqrestore(&cpufreq_driver_lock, flags);
+
+		list_for_each_entry(policy, &cpufreq_policy_list, policy_list)
+			if (__cpufreq_governor(policy, CPUFREQ_GOV_START) ||
+					__cpufreq_governor(policy,
+						CPUFREQ_GOV_LIMITS))
+				pr_err("%s: Failed to start governor for policy: %p\n",
+						__func__, policy);
+	}
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block cpufreq_pm_notifier = {
+	.notifier_call = cpufreq_pm_notify,
+};
+
 /**
  * cpufreq_bp_suspend - Prepare the boot CPU for system suspend.
  *
@@ -1752,6 +1804,8 @@ EXPORT_SYMBOL_GPL(cpufreq_driver_target);
 static int __cpufreq_governor(struct cpufreq_policy *policy,
 					unsigned int event)
 {
+	unsigned long flags;
+	bool is_suspended;
 	int ret;
 
 	/* Only must be defined when default governor is known to have latency
@@ -1764,6 +1818,14 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
 	struct cpufreq_governor *gov = NULL;
 #endif
 
+	/* Don't start any governor operations if we are entering suspend */
+	read_lock_irqsave(&cpufreq_driver_lock, flags);
+	is_suspended = cpufreq_suspended;
+	read_unlock_irqrestore(&cpufreq_driver_lock, flags);
+
+	if (is_suspended)
+		return 0;
+
 	if (policy->governor->max_transition_latency &&
 	    policy->cpuinfo.transition_latency >
 	    policy->governor->max_transition_latency) {
@@ -2222,6 +2284,7 @@ static int __init cpufreq_core_init(void)
 	cpufreq_global_kobject = kobject_create();
 	BUG_ON(!cpufreq_global_kobject);
 	register_syscore_ops(&cpufreq_syscore_ops);
+	register_pm_notifier(&cpufreq_pm_notifier);
 
 	return 0;
 }
-- 
1.7.12.rc2.18.g61b472e

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