int dev_pm_opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
{
	struct device_opp *dev_opp = NULL;
	struct dev_pm_opp *opp, *new_opp;
	struct list_head *head;

	/* allocate new OPP node */
	new_opp = kzalloc(sizeof(*new_opp), GFP_KERNEL);
	if (!new_opp) {
		dev_warn(dev, "%s: Unable to create new OPP node\n", __func__);
		return -ENOMEM;
	}

	/* Hold our list modification lock here */
	mutex_lock(&dev_opp_list_lock);

	/* Check for existing list for 'dev' */
	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp)) {
		/*
		 * Allocate a new device OPP table. In the infrequent case
		 * where a new device is needed to be added, we pay this
		 * penalty.
		 */
		dev_opp = kzalloc(sizeof(struct device_opp), GFP_KERNEL);
		if (!dev_opp) {
			mutex_unlock(&dev_opp_list_lock);
			kfree(new_opp);
			dev_warn(dev,
				"%s: Unable to create device OPP structure\n",
				__func__);
			return -ENOMEM;
		}

		dev_opp->dev = dev;
		srcu_init_notifier_head(&dev_opp->head);
		INIT_LIST_HEAD(&dev_opp->opp_list);

		/* Secure the device list modification */
		list_add_rcu(&dev_opp->node, &dev_opp_list);
	}

	/* populate the opp table */
	new_opp->dev_opp = dev_opp;
	new_opp->rate = freq;
	new_opp->u_volt = u_volt;
	new_opp->available = true;

	/*
	 * Insert new OPP in order of increasing frequency
	 * and discard if already present
	 */
	head = &dev_opp->opp_list;
	list_for_each_entry_rcu(opp, &dev_opp->opp_list, node) {
		if (new_opp->rate <= opp->rate)
			break;
		else
			head = &opp->node;
	}

	/* Duplicate OPPs ? */
	if (new_opp->rate == opp->rate) {
		int ret = opp->available && new_opp->u_volt == opp->u_volt ?
			0 : -EEXIST;

		dev_warn(dev, "%s: duplicate OPPs detected. Existing: freq: %lu, volt: %lu, enabled: %d. New: freq: %lu, volt: %lu, enabled: %d\n",
			 __func__, opp->rate, opp->u_volt, opp->available,
			 new_opp->rate, new_opp->u_volt, new_opp->available);
		mutex_unlock(&dev_opp_list_lock);
		kfree(new_opp);
		return ret;
	}

	list_add_rcu(&new_opp->node, head);
	mutex_unlock(&dev_opp_list_lock);

	/*
	 * Notify the changes in the availability of the operable
	 * frequency/voltage list.
	 */
	srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_ADD, new_opp);
	return 0;
}

static int opp_set_availability(struct device *dev, unsigned long freq,
		bool availability_req)
{
	struct device_opp *tmp_dev_opp, *dev_opp = ERR_PTR(-ENODEV);
	struct dev_pm_opp *new_opp, *tmp_opp, *opp = ERR_PTR(-ENODEV);
	int r = 0;

	/* keep the node allocated */
	new_opp = kmalloc(sizeof(*new_opp), GFP_KERNEL);
	if (!new_opp) {
		dev_warn(dev, "%s: Unable to create OPP\n", __func__);
		return -ENOMEM;
	}

	mutex_lock(&dev_opp_list_lock);

	/* Find the device_opp */
	list_for_each_entry(tmp_dev_opp, &dev_opp_list, node) {
		if (dev == tmp_dev_opp->dev) {
			dev_opp = tmp_dev_opp;
			break;
		}
	}
	if (IS_ERR(dev_opp)) {
		r = PTR_ERR(dev_opp);
		dev_warn(dev, "%s: Device OPP not found (%d)\n", __func__, r);
		goto unlock;
	}

	/* Do we have the frequency? */
	list_for_each_entry(tmp_opp, &dev_opp->opp_list, node) {
		if (tmp_opp->rate == freq) {
			opp = tmp_opp;
			break;
		}
	}
	if (IS_ERR(opp)) {
		r = PTR_ERR(opp);
		goto unlock;
	}

	/* Is update really needed? */
	if (opp->available == availability_req)
		goto unlock;
	/* copy the old data over */
	*new_opp = *opp;

	/* plug in new node */
	new_opp->available = availability_req;

	list_replace_rcu(&opp->node, &new_opp->node);
	mutex_unlock(&dev_opp_list_lock);
	kfree_rcu(opp, head);

	/* Notify the change of the OPP availability */
	if (availability_req)
		srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_ENABLE,
					 new_opp);
	else
		srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_DISABLE,
					 new_opp);

	return 0;

unlock:
	mutex_unlock(&dev_opp_list_lock);
	kfree(new_opp);
	return r;
}

• of_init_opp_table（从dt中初始化opp table）
  

cpu@0 { compatible = "arm,cortex-a9";
	reg = <0>;
	next-level-cache = <&L2>;
	operating-points = < 
                  /* kHz    uV */ 
                  792000  1100000 
                  396000  950000 
                  198000  850000 
           >; 
}; 

int of_init_opp_table(struct device *dev)
{
	const struct property *prop;
	const __be32 *val;
	int nr;

	prop = of_find_property(dev->of_node, "operating-points", NULL);
	if (!prop)
		return -ENODEV;
	if (!prop->value)
		return -ENODATA;

	/*
	 * Each OPP is a set of tuples consisting of frequency and
	 * voltage like <freq-kHz vol-uV>.
	 */
	nr = prop->length / sizeof(u32);
	if (nr % 2) {
		dev_err(dev, "%s: Invalid OPP list\n", __func__);
		return -EINVAL;
	}

	val = prop->value;
	while (nr) {
		unsigned long freq = be32_to_cpup(val++) * 1000;
		unsigned long volt = be32_to_cpup(val++);

		if (dev_pm_opp_add(dev, freq, volt))
			dev_warn(dev, "%s: Failed to add OPP %ld\n",
				 __func__, freq);
		nr -= 2;
	}

	return 0;
}