PM: Introduce devfreq: generic DVFS framework with device-specific OPPs

With OPPs, a device may have multiple operable frequency and voltage
sets. However, there can be multiple possible operable sets and a system
will need to choose one from them. In order to reduce the power
consumption (by reducing frequency and voltage) without affecting the
performance too much, a Dynamic Voltage and Frequency Scaling (DVFS)
scheme may be used.

This patch introduces the DVFS capability to non-CPU devices with OPPs.
DVFS is a techique whereby the frequency and supplied voltage of a
device is adjusted on-the-fly. DVFS usually sets the frequency as low
as possible with given conditions (such as QoS assurance) and adjusts
voltage according to the chosen frequency in order to reduce power
consumption and heat dissipation.

The generic DVFS for devices, devfreq, may appear quite similar with
/drivers/cpufreq.  However, cpufreq does not allow to have multiple
devices registered and is not suitable to have multiple heterogenous
devices with different (but simple) governors.

Normally, DVFS mechanism controls frequency based on the demand for
the device, and then, chooses voltage based on the chosen frequency.
devfreq also controls the frequency based on the governor's frequency
recommendation and let OPP pick up the pair of frequency and voltage
based on the recommended frequency. Then, the chosen OPP is passed to
device driver's "target" callback.

When PM QoS is going to be used with the devfreq device, the device
driver should enable OPPs that are appropriate with the current PM QoS
requests. In order to do so, the device driver may call opp_enable and
opp_disable at the notifier callback of PM QoS so that PM QoS's
update_target() call enables the appropriate OPPs. Note that at least
one of OPPs should be enabled at any time; be careful when there is a
transition.

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Mike Turquette <mturquette@ti.com>
Acked-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

1 files changed, 532 insertions, 0 deletions

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
new file mode 100644
index 000000000000..f3100b19f798
--- /dev/null
+++ b/drivers/devfreq/devfreq.c
@@ -0,0 +1,532 @@
+/*
+ * devfreq: Generic Dynamic Voltage and Frequency Scaling (DVFS) Framework
+ *          for Non-CPU Devices.
+ *
+ * Copyright (C) 2011 Samsung Electronics
+ *      MyungJoo Ham <myungjoo.ham@samsung.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/errno.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/opp.h>
+#include <linux/devfreq.h>
+#include <linux/workqueue.h>
+#include <linux/platform_device.h>
+#include <linux/list.h>
+#include <linux/printk.h>
+#include <linux/hrtimer.h>
+#include "governor.h"
+
+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.
+ */
+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);
+static DEFINE_MUTEX(devfreq_list_lock);
+
+/**
+ * find_device_devfreq() - find devfreq struct using device pointer
+ * @dev:        device pointer used to lookup device devfreq.
+ *
+ * Search the list of device devfreqs and return the matched device's
+ * devfreq info. devfreq_list_lock should be held by the caller.
+ */
+static struct devfreq *find_device_devfreq(struct device *dev)
+{
+        struct devfreq *tmp_devfreq;
+
+        if (unlikely(IS_ERR_OR_NULL(dev))) {
+                pr_err("DEVFREQ: %s: Invalid parameters\n", __func__);
+                return ERR_PTR(-EINVAL);
+        }
+        WARN(!mutex_is_locked(&devfreq_list_lock),
+             "devfreq_list_lock must be locked.");
+
+        list_for_each_entry(tmp_devfreq, &devfreq_list, node) {
+                if (tmp_devfreq->dev.parent == dev)
+                        return tmp_devfreq;
+        }
+
+        return ERR_PTR(-ENODEV);
+}
+
+/**
+ * update_devfreq() - Reevaluate the device and configure frequency.
+ * @devfreq:    the devfreq instance.
+ *
+ * Note: Lock devfreq->lock before calling update_devfreq
+ *       This function is exported for governors.
+ */
+int update_devfreq(struct devfreq *devfreq)
+{
+        unsigned long freq;
+        int err = 0;
+
+        if (!mutex_is_locked(&devfreq->lock)) {
+                WARN(true, "devfreq->lock must be locked by the caller.\n");
+                return -EINVAL;
+        }
+
+        /* Reevaluate the proper frequency */
+        err = devfreq->governor->get_target_freq(devfreq, &freq);
+        if (err)
+                return err;
+
+        err = devfreq->profile->target(devfreq->dev.parent, &freq);
+        if (err)
+                return err;
+
+        devfreq->previous_freq = freq;
+        return err;
+}
+
+/**
+ * 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)
+ * @type        not used
+ * @devp        not used
+ *
+ * Called by a notifier that uses devfreq->nb.
+ */
+static int devfreq_notifier_call(struct notifier_block *nb, unsigned long type,
+                                 void *devp)
+{
+        struct devfreq *devfreq = container_of(nb, struct devfreq, nb);
+        int ret;
+
+        mutex_lock(&devfreq->lock);
+        ret = update_devfreq(devfreq);
+        mutex_unlock(&devfreq->lock);
+
+        return ret;
+}
+
+/**
+ * _remove_devfreq() - Remove devfreq from the device.
+ * @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");
+                return;
+        }
+
+        if (devfreq->being_removed)
+                return;
+
+        devfreq->being_removed = true;
+
+        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);
+}
+
+/**
+ * devfreq_dev_release() - Callback for struct device to release the device.
+ * @dev:        the devfreq device
+ *
+ * This calls _remove_devfreq() if _remove_devfreq() is not called.
+ * Note that devfreq_dev_release() could be called by _remove_devfreq() as
+ * well as by others unregistering the device.
+ */
+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;
+        }
+}
+
+/**
+ * devfreq_add_device() - Add devfreq feature to the device
+ * @dev:        the device to add devfreq feature.
+ * @profile:    device-specific profile to run devfreq.
+ * @governor:   the policy to choose frequency.
+ * @data:       private data for the governor. The devfreq framework does not
+ *              touch this value.
+ */
+struct devfreq *devfreq_add_device(struct device *dev,
+                                   struct devfreq_dev_profile *profile,
+                                   const struct devfreq_governor *governor,
+                                   void *data)
+{
+        struct devfreq *devfreq;
+        int err = 0;
+
+        if (!dev || !profile || !governor) {
+                dev_err(dev, "%s: Invalid parameters.\n", __func__);
+                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 out;
+                }
+        }
+
+        devfreq = kzalloc(sizeof(struct devfreq), GFP_KERNEL);
+        if (!devfreq) {
+                dev_err(dev, "%s: Unable to create devfreq for the device\n",
+                        __func__);
+                err = -ENOMEM;
+                goto out;
+        }
+
+        mutex_init(&devfreq->lock);
+        mutex_lock(&devfreq->lock);
+        devfreq->dev.parent = dev;
+        devfreq->dev.class = devfreq_class;
+        devfreq->dev.release = devfreq_dev_release;
+        devfreq->profile = profile;
+        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);
+                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);
+
+        if (devfreq_wq && devfreq->next_polling && !polling) {
+                polling = true;
+                queue_delayed_work(devfreq_wq, &devfreq_work,
+                                   devfreq->next_polling);
+        }
+        mutex_unlock(&devfreq_list_lock);
+        goto out;
+err_init:
+        device_unregister(&devfreq->dev);
+err_dev:
+        mutex_unlock(&devfreq->lock);
+        kfree(devfreq);
+out:
+        if (err)
+                return ERR_PTR(err);
+        else
+                return devfreq;
+}
+
+/**
+ * devfreq_remove_device() - Remove devfreq feature from a device.
+ * @devfreq     the devfreq instance to be removed
+ */
+int devfreq_remove_device(struct devfreq *devfreq)
+{
+        if (!devfreq)
+                return -EINVAL;
+
+        if (!devfreq->governor->no_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 (!devfreq->governor->no_central_polling)
+                mutex_unlock(&devfreq_list_lock);
+
+        return 0;
+}
+
+/**
+ * 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_DELAYED_WORK_DEFERRABLE(&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");
+        if (IS_ERR(devfreq_class)) {
+                pr_err("%s: couldn't create class\n", __FILE__);
+                return PTR_ERR(devfreq_class);
+        }
+        return 0;
+}
+subsys_initcall(devfreq_init);
+
+static void __exit devfreq_exit(void)
+{
+        class_destroy(devfreq_class);
+}
+module_exit(devfreq_exit);
+
+/*
+ * The followings are helper functions for devfreq user device drivers with
+ * OPP framework.
+ */
+
+/**
+ * devfreq_recommended_opp() - Helper function to get proper OPP for the
+ *                           freq value given to target callback.
+ * @dev         The devfreq user device. (parent of devfreq)
+ * @freq        The frequency given to target function
+ *
+ */
+struct opp *devfreq_recommended_opp(struct device *dev, unsigned long *freq)
+{
+        struct opp *opp = opp_find_freq_ceil(dev, freq);
+
+        if (opp == ERR_PTR(-ENODEV))
+                opp = opp_find_freq_floor(dev, freq);
+        return opp;
+}
+
+/**
+ * devfreq_register_opp_notifier() - Helper function to get devfreq notified
+ *                                 for any changes in the OPP availability
+ *                                 changes
+ * @dev         The devfreq user device. (parent of devfreq)
+ * @devfreq     The devfreq object.
+ */
+int devfreq_register_opp_notifier(struct device *dev, struct devfreq *devfreq)
+{
+        struct srcu_notifier_head *nh = opp_get_notifier(dev);
+
+        if (IS_ERR(nh))
+                return PTR_ERR(nh);
+        return srcu_notifier_chain_register(nh, &devfreq->nb);
+}
+
+/**
+ * devfreq_unregister_opp_notifier() - Helper function to stop getting devfreq
+ *                                   notified for any changes in the OPP
+ *                                   availability changes anymore.
+ * @dev         The devfreq user device. (parent of devfreq)
+ * @devfreq     The devfreq object.
+ *
+ * At exit() callback of devfreq_dev_profile, this must be included if
+ * devfreq_recommended_opp is used.
+ */
+int devfreq_unregister_opp_notifier(struct device *dev, struct devfreq *devfreq)
+{
+        struct srcu_notifier_head *nh = opp_get_notifier(dev);
+
+        if (IS_ERR(nh))
+                return PTR_ERR(nh);
+        return srcu_notifier_chain_unregister(nh, &devfreq->nb);
+}
+
+MODULE_AUTHOR("MyungJoo Ham <myungjoo.ham@samsung.com>");
+MODULE_DESCRIPTION("devfreq class support");
+MODULE_LICENSE("GPL");