PM / devfreq: Core updates to support devices which can idle

Prepare devfreq core framework to support devices which
can idle. When device idleness is detected perhaps through
runtime-pm, need some mechanism to suspend devfreq load
monitoring and resume back when device is online. Present
code continues monitoring unless device is removed from
devfreq core.

This patch introduces following design changes,

 - use per device work instead of global work to monitor device
   load. This enables suspend/resume of device devfreq and
   reduces monitoring code complexity.
 - decouple delayed work based load monitoring logic from core
   by introducing helpers functions to be used by governors. This
   provides flexibility for governors either to use delayed work
   based monitoring functions or to implement their own mechanism.
 - devfreq core interacts with governors via events to perform
   specific actions. These events include start/stop devfreq.
   This sets ground for adding suspend/resume events.

The devfreq apis are not modified and are kept intact.

Signed-off-by: Rajagopal Venkat <rajagopal.venkat@linaro.org>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 189 insertions, 253 deletions

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index b146d76f04cf..1aaf1aeb1f1d 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -30,17 +30,11 @@
 struct class *devfreq_class;
 
 /*
- * devfreq_work periodically monitors every registered device.
- * The minimum polling interval is one jiffy. The polling interval is
- * determined by the minimum polling period among all polling devfreq
- * devices. The resolution of polling interval is one jiffy.
+ * devfreq core provides delayed work based load monitoring helper
+ * functions. Governors can use these or can implement their own
+ * monitoring mechanism.
  */
-static bool polling;
 static struct workqueue_struct *devfreq_wq;
-static struct delayed_work devfreq_work;
-
-/* wait removing if this is to be removed */
-static struct devfreq *wait_remove_device;
 
 /* The list of all device-devfreq */
 static LIST_HEAD(devfreq_list);
@@ -72,6 +66,8 @@ static struct devfreq *find_device_devfreq(struct device *dev)
 	return ERR_PTR(-ENODEV);
 }
 
+/* Load monitoring helper functions for governors use */
+
 /**
  * update_devfreq() - Reevaluate the device and configure frequency.
  * @devfreq:	the devfreq instance.
@@ -121,6 +117,152 @@ int update_devfreq(struct devfreq *devfreq)
 }
 
 /**
+ * devfreq_monitor() - Periodically poll devfreq objects.
+ * @work:	the work struct used to run devfreq_monitor periodically.
+ *
+ */
+static void devfreq_monitor(struct work_struct *work)
+{
+	int err;
+	struct devfreq *devfreq = container_of(work,
+					struct devfreq, work.work);
+
+	mutex_lock(&devfreq->lock);
+	err = update_devfreq(devfreq);
+	if (err)
+		dev_err(&devfreq->dev, "dvfs failed with (%d) error\n", err);
+
+	queue_delayed_work(devfreq_wq, &devfreq->work,
+				msecs_to_jiffies(devfreq->profile->polling_ms));
+	mutex_unlock(&devfreq->lock);
+}
+
+/**
+ * devfreq_monitor_start() - Start load monitoring of devfreq instance
+ * @devfreq:	the devfreq instance.
+ *
+ * Helper function for starting devfreq device load monitoing. By
+ * default delayed work based monitoring is supported. Function
+ * to be called from governor in response to DEVFREQ_GOV_START
+ * event when device is added to devfreq framework.
+ */
+void devfreq_monitor_start(struct devfreq *devfreq)
+{
+	INIT_DEFERRABLE_WORK(&devfreq->work, devfreq_monitor);
+	if (devfreq->profile->polling_ms)
+		queue_delayed_work(devfreq_wq, &devfreq->work,
+			msecs_to_jiffies(devfreq->profile->polling_ms));
+}
+
+/**
+ * devfreq_monitor_stop() - Stop load monitoring of a devfreq instance
+ * @devfreq:	the devfreq instance.
+ *
+ * Helper function to stop devfreq device load monitoing. Function
+ * to be called from governor in response to DEVFREQ_GOV_STOP
+ * event when device is removed from devfreq framework.
+ */
+void devfreq_monitor_stop(struct devfreq *devfreq)
+{
+	cancel_delayed_work_sync(&devfreq->work);
+}
+
+/**
+ * devfreq_monitor_suspend() - Suspend load monitoring of a devfreq instance
+ * @devfreq:	the devfreq instance.
+ *
+ * Helper function to suspend devfreq device load monitoing. Function
+ * to be called from governor in response to DEVFREQ_GOV_SUSPEND
+ * event or when polling interval is set to zero.
+ *
+ * Note: Though this function is same as devfreq_monitor_stop(),
+ * intentionally kept separate to provide hooks for collecting
+ * transition statistics.
+ */
+void devfreq_monitor_suspend(struct devfreq *devfreq)
+{
+	mutex_lock(&devfreq->lock);
+	if (devfreq->stop_polling) {
+		mutex_unlock(&devfreq->lock);
+		return;
+	}
+
+	devfreq->stop_polling = true;
+	mutex_unlock(&devfreq->lock);
+	cancel_delayed_work_sync(&devfreq->work);
+}
+
+/**
+ * devfreq_monitor_resume() - Resume load monitoring of a devfreq instance
+ * @devfreq:    the devfreq instance.
+ *
+ * Helper function to resume devfreq device load monitoing. Function
+ * to be called from governor in response to DEVFREQ_GOV_RESUME
+ * event or when polling interval is set to non-zero.
+ */
+void devfreq_monitor_resume(struct devfreq *devfreq)
+{
+	mutex_lock(&devfreq->lock);
+	if (!devfreq->stop_polling)
+		goto out;
+
+	if (!delayed_work_pending(&devfreq->work) &&
+			devfreq->profile->polling_ms)
+		queue_delayed_work(devfreq_wq, &devfreq->work,
+			msecs_to_jiffies(devfreq->profile->polling_ms));
+	devfreq->stop_polling = false;
+
+out:
+	mutex_unlock(&devfreq->lock);
+}
+
+/**
+ * devfreq_interval_update() - Update device devfreq monitoring interval
+ * @devfreq:    the devfreq instance.
+ * @delay:      new polling interval to be set.
+ *
+ * Helper function to set new load monitoring polling interval. Function
+ * to be called from governor in response to DEVFREQ_GOV_INTERVAL event.
+ */
+void devfreq_interval_update(struct devfreq *devfreq, unsigned int *delay)
+{
+	unsigned int cur_delay = devfreq->profile->polling_ms;
+	unsigned int new_delay = *delay;
+
+	mutex_lock(&devfreq->lock);
+	devfreq->profile->polling_ms = new_delay;
+
+	if (devfreq->stop_polling)
+		goto out;
+
+	/* if new delay is zero, stop polling */
+	if (!new_delay) {
+		mutex_unlock(&devfreq->lock);
+		cancel_delayed_work_sync(&devfreq->work);
+		return;
+	}
+
+	/* if current delay is zero, start polling with new delay */
+	if (!cur_delay) {
+		queue_delayed_work(devfreq_wq, &devfreq->work,
+			msecs_to_jiffies(devfreq->profile->polling_ms));
+		goto out;
+	}
+
+	/* if current delay is greater than new delay, restart polling */
+	if (cur_delay > new_delay) {
+		mutex_unlock(&devfreq->lock);
+		cancel_delayed_work_sync(&devfreq->work);
+		mutex_lock(&devfreq->lock);
+		if (!devfreq->stop_polling)
+			queue_delayed_work(devfreq_wq, &devfreq->work,
+			      msecs_to_jiffies(devfreq->profile->polling_ms));
+	}
+out:
+	mutex_unlock(&devfreq->lock);
+}
+
+/**
  * devfreq_notifier_call() - Notify that the device frequency requirements
  *			   has been changed out of devfreq framework.
  * @nb		the notifier_block (supposed to be devfreq->nb)
@@ -143,59 +285,32 @@ static int devfreq_notifier_call(struct notifier_block *nb, unsigned long type,
 }
 
 /**
- * _remove_devfreq() - Remove devfreq from the device.
+ * _remove_devfreq() - Remove devfreq from the list and release its resources.
  * @devfreq:	the devfreq struct
  * @skip:	skip calling device_unregister().
- *
- * Note that the caller should lock devfreq->lock before calling
- * this. _remove_devfreq() will unlock it and free devfreq
- * internally. devfreq_list_lock should be locked by the caller
- * as well (not relased at return)
- *
- * Lock usage:
- * devfreq->lock: locked before call.
- *		  unlocked at return (and freed)
- * devfreq_list_lock: locked before call.
- *		      kept locked at return.
- *		      if devfreq is centrally polled.
- *
- * Freed memory:
- * devfreq
  */
 static void _remove_devfreq(struct devfreq *devfreq, bool skip)
 {
-	if (!mutex_is_locked(&devfreq->lock)) {
-		WARN(true, "devfreq->lock must be locked by the caller.\n");
-		return;
-	}
-	if (!devfreq->governor->no_central_polling &&
-	    !mutex_is_locked(&devfreq_list_lock)) {
-		WARN(true, "devfreq_list_lock must be locked by the caller.\n");
+	mutex_lock(&devfreq_list_lock);
+	if (IS_ERR(find_device_devfreq(devfreq->dev.parent))) {
+		mutex_unlock(&devfreq_list_lock);
+		dev_warn(&devfreq->dev, "releasing devfreq which doesn't exist\n");
 		return;
 	}
+	list_del(&devfreq->node);
+	mutex_unlock(&devfreq_list_lock);
 
-	if (devfreq->being_removed)
-		return;
-
-	devfreq->being_removed = true;
+	devfreq->governor->event_handler(devfreq, DEVFREQ_GOV_STOP, NULL);
 
 	if (devfreq->profile->exit)
 		devfreq->profile->exit(devfreq->dev.parent);
 
-	if (devfreq->governor->exit)
-		devfreq->governor->exit(devfreq);
-
 	if (!skip && get_device(&devfreq->dev)) {
 		device_unregister(&devfreq->dev);
 		put_device(&devfreq->dev);
 	}
 
-	if (!devfreq->governor->no_central_polling)
-		list_del(&devfreq->node);
-
-	mutex_unlock(&devfreq->lock);
 	mutex_destroy(&devfreq->lock);
-
 	kfree(devfreq);
 }
 
@@ -210,130 +325,8 @@ static void _remove_devfreq(struct devfreq *devfreq, bool skip)
 static void devfreq_dev_release(struct device *dev)
 {
 	struct devfreq *devfreq = to_devfreq(dev);
-	bool central_polling = !devfreq->governor->no_central_polling;
-
-	/*
-	 * If devfreq_dev_release() was called by device_unregister() of
-	 * _remove_devfreq(), we cannot mutex_lock(&devfreq->lock) and
-	 * being_removed is already set. This also partially checks the case
-	 * where devfreq_dev_release() is called from a thread other than
-	 * the one called _remove_devfreq(); however, this case is
-	 * dealt completely with another following being_removed check.
-	 *
-	 * Because being_removed is never being
-	 * unset, we do not need to worry about race conditions on
-	 * being_removed.
-	 */
-	if (devfreq->being_removed)
-		return;
 
-	if (central_polling)
-		mutex_lock(&devfreq_list_lock);
-
-	mutex_lock(&devfreq->lock);
-
-	/*
-	 * Check being_removed flag again for the case where
-	 * devfreq_dev_release() was called in a thread other than the one
-	 * possibly called _remove_devfreq().
-	 */
-	if (devfreq->being_removed) {
-		mutex_unlock(&devfreq->lock);
-		goto out;
-	}
-
-	/* devfreq->lock is unlocked and removed in _removed_devfreq() */
 	_remove_devfreq(devfreq, true);
-
-out:
-	if (central_polling)
-		mutex_unlock(&devfreq_list_lock);
-}
-
-/**
- * devfreq_monitor() - Periodically poll devfreq objects.
- * @work: the work struct used to run devfreq_monitor periodically.
- *
- */
-static void devfreq_monitor(struct work_struct *work)
-{
-	static unsigned long last_polled_at;
-	struct devfreq *devfreq, *tmp;
-	int error;
-	unsigned long jiffies_passed;
-	unsigned long next_jiffies = ULONG_MAX, now = jiffies;
-	struct device *dev;
-
-	/* Initially last_polled_at = 0, polling every device at bootup */
-	jiffies_passed = now - last_polled_at;
-	last_polled_at = now;
-	if (jiffies_passed == 0)
-		jiffies_passed = 1;
-
-	mutex_lock(&devfreq_list_lock);
-	list_for_each_entry_safe(devfreq, tmp, &devfreq_list, node) {
-		mutex_lock(&devfreq->lock);
-		dev = devfreq->dev.parent;
-
-		/* Do not remove tmp for a while */
-		wait_remove_device = tmp;
-
-		if (devfreq->governor->no_central_polling ||
-		    devfreq->next_polling == 0) {
-			mutex_unlock(&devfreq->lock);
-			continue;
-		}
-		mutex_unlock(&devfreq_list_lock);
-
-		/*
-		 * Reduce more next_polling if devfreq_wq took an extra
-		 * delay. (i.e., CPU has been idled.)
-		 */
-		if (devfreq->next_polling <= jiffies_passed) {
-			error = update_devfreq(devfreq);
-
-			/* Remove a devfreq with an error. */
-			if (error && error != -EAGAIN) {
-
-				dev_err(dev, "Due to update_devfreq error(%d), devfreq(%s) is removed from the device\n",
-					error, devfreq->governor->name);
-
-				/*
-				 * Unlock devfreq before locking the list
-				 * in order to avoid deadlock with
-				 * find_device_devfreq or others
-				 */
-				mutex_unlock(&devfreq->lock);
-				mutex_lock(&devfreq_list_lock);
-				/* Check if devfreq is already removed */
-				if (IS_ERR(find_device_devfreq(dev)))
-					continue;
-				mutex_lock(&devfreq->lock);
-				/* This unlocks devfreq->lock and free it */
-				_remove_devfreq(devfreq, false);
-				continue;
-			}
-			devfreq->next_polling = devfreq->polling_jiffies;
-		} else {
-			devfreq->next_polling -= jiffies_passed;
-		}
-
-		if (devfreq->next_polling)
-			next_jiffies = (next_jiffies > devfreq->next_polling) ?
-					devfreq->next_polling : next_jiffies;
-
-		mutex_unlock(&devfreq->lock);
-		mutex_lock(&devfreq_list_lock);
-	}
-	wait_remove_device = NULL;
-	mutex_unlock(&devfreq_list_lock);
-
-	if (next_jiffies > 0 && next_jiffies < ULONG_MAX) {
-		polling = true;
-		queue_delayed_work(devfreq_wq, &devfreq_work, next_jiffies);
-	} else {
-		polling = false;
-	}
 }
 
 /**
@@ -357,16 +350,13 @@ struct devfreq *devfreq_add_device(struct device *dev,
 		return ERR_PTR(-EINVAL);
 	}
 
-
-	if (!governor->no_central_polling) {
-		mutex_lock(&devfreq_list_lock);
-		devfreq = find_device_devfreq(dev);
-		mutex_unlock(&devfreq_list_lock);
-		if (!IS_ERR(devfreq)) {
-			dev_err(dev, "%s: Unable to create devfreq for the device. It already has one.\n", __func__);
-			err = -EINVAL;
-			goto err_out;
-		}
+	mutex_lock(&devfreq_list_lock);
+	devfreq = find_device_devfreq(dev);
+	mutex_unlock(&devfreq_list_lock);
+	if (!IS_ERR(devfreq)) {
+		dev_err(dev, "%s: Unable to create devfreq for the device. It already has one.\n", __func__);
+		err = -EINVAL;
+		goto err_out;
 	}
 
 	devfreq = kzalloc(sizeof(struct devfreq), GFP_KERNEL);
@@ -386,48 +376,41 @@ struct devfreq *devfreq_add_device(struct device *dev,
 	devfreq->governor = governor;
 	devfreq->previous_freq = profile->initial_freq;
 	devfreq->data = data;
-	devfreq->next_polling = devfreq->polling_jiffies
-			      = msecs_to_jiffies(devfreq->profile->polling_ms);
 	devfreq->nb.notifier_call = devfreq_notifier_call;
 
 	dev_set_name(&devfreq->dev, dev_name(dev));
 	err = device_register(&devfreq->dev);
 	if (err) {
 		put_device(&devfreq->dev);
+		mutex_unlock(&devfreq->lock);
 		goto err_dev;
 	}
 
-	if (governor->init)
-		err = governor->init(devfreq);
-	if (err)
-		goto err_init;
-
 	mutex_unlock(&devfreq->lock);
 
-	if (governor->no_central_polling)
-		goto out;
-
 	mutex_lock(&devfreq_list_lock);
-
 	list_add(&devfreq->node, &devfreq_list);
+	mutex_unlock(&devfreq_list_lock);
 
-	if (devfreq_wq && devfreq->next_polling && !polling) {
-		polling = true;
-		queue_delayed_work(devfreq_wq, &devfreq_work,
-				   devfreq->next_polling);
+	err = devfreq->governor->event_handler(devfreq,
+				DEVFREQ_GOV_START, NULL);
+	if (err) {
+		dev_err(dev, "%s: Unable to start governor for the device\n",
+			__func__);
+		goto err_init;
 	}
-	mutex_unlock(&devfreq_list_lock);
-out:
+
 	return devfreq;
 
 err_init:
+	list_del(&devfreq->node);
 	device_unregister(&devfreq->dev);
 err_dev:
-	mutex_unlock(&devfreq->lock);
 	kfree(devfreq);
 err_out:
 	return ERR_PTR(err);
 }
+EXPORT_SYMBOL(devfreq_add_device);
 
 /**
  * devfreq_remove_device() - Remove devfreq feature from a device.
@@ -435,30 +418,14 @@ err_out:
  */
 int devfreq_remove_device(struct devfreq *devfreq)
 {
-	bool central_polling;
-
 	if (!devfreq)
 		return -EINVAL;
 
-	central_polling = !devfreq->governor->no_central_polling;
-
-	if (central_polling) {
-		mutex_lock(&devfreq_list_lock);
-		while (wait_remove_device == devfreq) {
-			mutex_unlock(&devfreq_list_lock);
-			schedule();
-			mutex_lock(&devfreq_list_lock);
-		}
-	}
-
-	mutex_lock(&devfreq->lock);
-	_remove_devfreq(devfreq, false); /* it unlocks devfreq->lock */
-
-	if (central_polling)
-		mutex_unlock(&devfreq_list_lock);
+	_remove_devfreq(devfreq, false);
 
 	return 0;
 }
+EXPORT_SYMBOL(devfreq_remove_device);
 
 static ssize_t show_governor(struct device *dev,
 			     struct device_attribute *attr, char *buf)
@@ -490,35 +457,13 @@ static ssize_t store_polling_interval(struct device *dev,
 	if (ret != 1)
 		goto out;
 
-	mutex_lock(&df->lock);
-	df->profile->polling_ms = value;
-	df->next_polling = df->polling_jiffies
-			 = msecs_to_jiffies(value);
-	mutex_unlock(&df->lock);
-
+	df->governor->event_handler(df, DEVFREQ_GOV_INTERVAL, &value);
 	ret = count;
 
-	if (df->governor->no_central_polling)
-		goto out;
-
-	mutex_lock(&devfreq_list_lock);
-	if (df->next_polling > 0 && !polling) {
-		polling = true;
-		queue_delayed_work(devfreq_wq, &devfreq_work,
-				   df->next_polling);
-	}
-	mutex_unlock(&devfreq_list_lock);
 out:
 	return ret;
 }
 
-static ssize_t show_central_polling(struct device *dev,
-				    struct device_attribute *attr, char *buf)
-{
-	return sprintf(buf, "%d\n",
-		       !to_devfreq(dev)->governor->no_central_polling);
-}
-
 static ssize_t store_min_freq(struct device *dev, struct device_attribute *attr,
 			      const char *buf, size_t count)
 {
@@ -590,7 +535,6 @@ static ssize_t show_max_freq(struct device *dev, struct device_attribute *attr,
 static struct device_attribute devfreq_attrs[] = {
 	__ATTR(governor, S_IRUGO, show_governor, NULL),
 	__ATTR(cur_freq, S_IRUGO, show_freq, NULL),
-	__ATTR(central_polling, S_IRUGO, show_central_polling, NULL),
 	__ATTR(polling_interval, S_IRUGO | S_IWUSR, show_polling_interval,
 	       store_polling_interval),
 	__ATTR(min_freq, S_IRUGO | S_IWUSR, show_min_freq, store_min_freq),
@@ -598,23 +542,6 @@ static struct device_attribute devfreq_attrs[] = {
 	{ },
 };
 
-/**
- * devfreq_start_polling() - Initialize data structure for devfreq framework and
- *			   start polling registered devfreq devices.
- */
-static int __init devfreq_start_polling(void)
-{
-	mutex_lock(&devfreq_list_lock);
-	polling = false;
-	devfreq_wq = create_freezable_workqueue("devfreq_wq");
-	INIT_DEFERRABLE_WORK(&devfreq_work, devfreq_monitor);
-	mutex_unlock(&devfreq_list_lock);
-
-	devfreq_monitor(&devfreq_work.work);
-	return 0;
-}
-late_initcall(devfreq_start_polling);
-
 static int __init devfreq_init(void)
 {
 	devfreq_class = class_create(THIS_MODULE, "devfreq");
@@ -622,7 +549,15 @@ static int __init devfreq_init(void)
 		pr_err("%s: couldn't create class\n", __FILE__);
 		return PTR_ERR(devfreq_class);
 	}
+
+	devfreq_wq = create_freezable_workqueue("devfreq_wq");
+	if (IS_ERR(devfreq_wq)) {
+		class_destroy(devfreq_class);
+		pr_err("%s: couldn't create workqueue\n", __FILE__);
+		return PTR_ERR(devfreq_wq);
+	}
 	devfreq_class->dev_attrs = devfreq_attrs;
+
 	return 0;
 }
 subsys_initcall(devfreq_init);
@@ -630,6 +565,7 @@ subsys_initcall(devfreq_init);
 static void __exit devfreq_exit(void)
 {
 	class_destroy(devfreq_class);
+	destroy_workqueue(devfreq_wq);
 }
 module_exit(devfreq_exit);