drivers/devfreq/governor_bw_hwmon.c - kernel/msm.git - Git at Google

 /*
  * Copyright (c) 2013-2014, The Linux Foundation. All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 and
  * only version 2 as published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  */

 #define pr_fmt(fmt) "bw-hwmon: " fmt

 #include <linux/kernel.h>
 #include <linux/sizes.h>
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/io.h>
 #include <linux/delay.h>
 #include <linux/ktime.h>
 #include <linux/time.h>
 #include <linux/err.h>
 #include <linux/errno.h>
 #include <linux/mutex.h>
 #include <linux/interrupt.h>
 #include <linux/platform_device.h>
 #include <linux/of.h>
 #include <linux/devfreq.h>
 #include "governor.h"
 #include "governor_bw_hwmon.h"

 struct hwmon_node {
 	unsigned int tolerance_percent;
 	unsigned int guard_band_mbps;
 	unsigned int decay_rate;
 	unsigned int io_percent;
 	unsigned int bw_step;
 	unsigned long prev_ab;
 	unsigned long *dev_ab;
 	ktime_t prev_ts;
 	bool mon_started;
 	struct list_head list;
 	void *orig_data;
 	struct bw_hwmon *hw;
 	struct devfreq_governor *gov;
 	struct attribute_group *attr_grp;
 };

 static LIST_HEAD(hwmon_list);
 static DEFINE_MUTEX(list_lock);

 static int use_cnt;
 static DEFINE_MUTEX(state_lock);

 #define show_attr(name) \
 static ssize_t show_##name(struct device *dev,				\
 			struct device_attribute *attr, char *buf)	\
 {									\
 	struct devfreq *df = to_devfreq(dev);				\
 	struct hwmon_node *hw = df->data;				\
 	return snprintf(buf, PAGE_SIZE, "%u\n", hw->name);		\
 }

 #define store_attr(name, _min, _max) \
 static ssize_t store_##name(struct device *dev,				\
 			struct device_attribute *attr, const char *buf,	\
 			size_t count)					\
 {									\
 	struct devfreq *df = to_devfreq(dev);				\
 	struct hwmon_node *hw = df->data;				\
 	int ret;							\
 	unsigned int val;						\
 	ret = sscanf(buf, "%u", &val);					\
 	if (ret != 1)							\
 		return -EINVAL;						\
 	val = max(val, _min);						\
 	val = min(val, _max);						\
 	hw->name = val;							\
 	return count;							\
 }

 #define gov_attr(__attr, min, max)	\
 show_attr(__attr)			\
 store_attr(__attr, min, max)		\
 static DEVICE_ATTR(__attr, 0644, show_##__attr, store_##__attr)

 #define MIN_MS	10U
 #define MAX_MS	500U

 static unsigned long measure_bw_and_set_irq(struct hwmon_node *node)
 {
 	ktime_t ts;
 	unsigned int us;
 	unsigned long mbps;
 	struct bw_hwmon *hw = node->hw;

 	/*
 	 * Since we are stopping the counters, we don't want this short work
 	 * to be interrupted by other tasks and cause the measurements to be
 	 * wrong. Not blocking interrupts to avoid affecting interrupt
 	 * latency and since they should be short anyway because they run in
 	 * atomic context.
 	 */
 	preempt_disable();

 	ts = ktime_get();
 	us = ktime_to_us(ktime_sub(ts, node->prev_ts));
 	if (!us)
 		us = 1;

 	mbps = hw->meas_bw_and_set_irq(hw, node->tolerance_percent, us);
 	node->prev_ts = ts;

 	preempt_enable();

 	dev_dbg(hw->df->dev.parent, "BW MBps = %6lu, period = %u\n", mbps, us);

 	return mbps;
 }

 static void compute_bw(struct hwmon_node *node, int mbps,
 			unsigned long *freq, unsigned long *ab)
 {
 	int new_bw;

 	mbps += node->guard_band_mbps;

 	if (mbps > node->prev_ab) {
 		new_bw = mbps;
 	} else {
 		new_bw = mbps * node->decay_rate
 			+ node->prev_ab * (100 - node->decay_rate);
 		new_bw /= 100;
 	}

 	node->prev_ab = new_bw;
 	if (ab)
 		*ab = roundup(new_bw, node->bw_step);
 	*freq = (new_bw * 100) / node->io_percent;
 }

 static struct hwmon_node *find_hwmon_node(struct devfreq *df)
 {
 	struct hwmon_node *node, *found = NULL;

 	mutex_lock(&list_lock);
 	list_for_each_entry(node, &hwmon_list, list)
 		if (node->hw->dev == df->dev.parent ||
 		    node->hw->of_node == df->dev.parent->of_node ||
 		    node->gov == df->governor) {
 			found = node;
 			break;
 		}
 	mutex_unlock(&list_lock);

 	return found;
 }

 #define TOO_SOON_US	(1 * USEC_PER_MSEC)
 int update_bw_hwmon(struct bw_hwmon *hwmon)
 {
 	struct devfreq *df;
 	struct hwmon_node *node;
 	ktime_t ts;
 	unsigned int us;
 	int ret;

 	if (!hwmon)
 		return -EINVAL;
 	df = hwmon->df;
 	if (!df)
 		return -ENODEV;
 	node = find_hwmon_node(df);
 	if (!node)
 		return -ENODEV;

 	if (!node->mon_started)
 		return -EBUSY;

 	dev_dbg(df->dev.parent, "Got update request\n");
 	devfreq_monitor_stop(df);

 	/*
 	 * Don't recalc bandwidth if the interrupt comes right after a
 	 * previous bandwidth calculation.  This is done for two reasons:
 	 *
 	 * 1. Sampling the BW during a very short duration can result in a
 	 *    very inaccurate measurement due to very short bursts.
 	 * 2. This can only happen if the limit was hit very close to the end
 	 *    of the previous sample period. Which means the current BW
 	 *    estimate is not very off and doesn't need to be readjusted.
 	 */
 	ts = ktime_get();
 	us = ktime_to_us(ktime_sub(ts, node->prev_ts));
 	if (us > TOO_SOON_US) {
 		mutex_lock(&df->lock);
 		ret = update_devfreq(df);
 		if (ret)
 			dev_err(df->dev.parent,
 				"Unable to update freq on request!\n");
 		mutex_unlock(&df->lock);
 	}

 	devfreq_monitor_start(df);

 	return 0;
 }

 static int start_monitoring(struct devfreq *df)
 {
 	int ret = 0;
 	unsigned long mbps;
 	struct device *dev = df->dev.parent;
 	struct hwmon_node *node;
 	struct bw_hwmon *hw;
 	struct devfreq_dev_status stat;

 	node = find_hwmon_node(df);
 	if (!node) {
 		dev_err(dev, "Unable to find HW monitor!\n");
 		return -ENODEV;
 	}
 	hw = node->hw;

 	stat.private_data = NULL;
 	if (df->profile->get_dev_status)
 		ret = df->profile->get_dev_status(df->dev.parent, &stat);
 	if (ret || !stat.private_data)
 		dev_warn(dev, "Device doesn't take AB votes!\n");
 	else
 		node->dev_ab = stat.private_data;

 	hw->df = df;
 	node->orig_data = df->data;
 	df->data = node;

 	node->prev_ts = ktime_get();
 	node->prev_ab = 0;
 	mbps = (df->previous_freq * node->io_percent) / 100;
 	ret = hw->start_hwmon(hw, mbps);
 	if (ret) {
 		dev_err(dev, "Unable to start HW monitor!\n");
 		goto err_start;
 	}

 	devfreq_monitor_start(df);
 	node->mon_started = true;

 	ret = sysfs_create_group(&df->dev.kobj, node->attr_grp);
 	if (ret)
 		goto err_sysfs;

 	return 0;

 err_sysfs:
 	node->mon_started = false;
 	devfreq_monitor_stop(df);
 	hw->stop_hwmon(hw);
 err_start:
 	df->data = node->orig_data;
 	node->orig_data = NULL;
 	hw->df = NULL;
 	node->dev_ab = NULL;
 	return ret;
 }

 static void stop_monitoring(struct devfreq *df)
 {
 	struct hwmon_node *node = df->data;
 	struct bw_hwmon *hw = node->hw;

 	sysfs_remove_group(&df->dev.kobj, node->attr_grp);
 	node->mon_started = false;
 	devfreq_monitor_stop(df);
 	hw->stop_hwmon(hw);
 	df->data = node->orig_data;
 	node->orig_data = NULL;
 	hw->df = NULL;
 	/*
 	 * Not all governors know about this additional extended device
 	 * configuration. To avoid leaving the extended configuration at a
 	 * stale state, set it to 0 and let the next governor take it from
 	 * there.
 	 */
 	if (node->dev_ab)
 		*node->dev_ab = 0;
 	node->dev_ab = NULL;
 }

 static int devfreq_bw_hwmon_get_freq(struct devfreq *df,
 					unsigned long *freq,
 					u32 *flag)
 {
 	unsigned long mbps;
 	struct hwmon_node *node = df->data;

 	mbps = measure_bw_and_set_irq(node);
 	compute_bw(node, mbps, freq, node->dev_ab);

 	return 0;
 }

 gov_attr(tolerance_percent, 0U, 30U);
 gov_attr(guard_band_mbps, 0U, 2000U);
 gov_attr(decay_rate, 0U, 100U);
 gov_attr(io_percent, 1U, 100U);
 gov_attr(bw_step, 50U, 1000U);

 static struct attribute *dev_attr[] = {
 	&dev_attr_tolerance_percent.attr,
 	&dev_attr_guard_band_mbps.attr,
 	&dev_attr_decay_rate.attr,
 	&dev_attr_io_percent.attr,
 	&dev_attr_bw_step.attr,
 	NULL,
 };

 static struct attribute_group dev_attr_group = {
 	.name = "bw_hwmon",
 	.attrs = dev_attr,
 };

 static int devfreq_bw_hwmon_ev_handler(struct devfreq *df,
 					unsigned int event, void *data)
 {
 	int ret;
 	unsigned int sample_ms;

 	switch (event) {
 	case DEVFREQ_GOV_START:
 		sample_ms = df->profile->polling_ms;
 		sample_ms = max(MIN_MS, sample_ms);
 		sample_ms = min(MAX_MS, sample_ms);
 		df->profile->polling_ms = sample_ms;

 		ret = start_monitoring(df);
 		if (ret)
 			return ret;

 		dev_dbg(df->dev.parent,
 			"Enabled dev BW HW monitor governor\n");
 		break;

 	case DEVFREQ_GOV_STOP:
 		stop_monitoring(df);
 		dev_dbg(df->dev.parent,
 			"Disabled dev BW HW monitor governor\n");
 		break;

 	case DEVFREQ_GOV_INTERVAL:
 		sample_ms = *(unsigned int *)data;
 		sample_ms = max(MIN_MS, sample_ms);
 		sample_ms = min(MAX_MS, sample_ms);
 		devfreq_interval_update(df, &sample_ms);
 		break;
 	}

 	return 0;
 }

 static struct devfreq_governor devfreq_gov_bw_hwmon = {
 	.name = "bw_hwmon",
 	.get_target_freq = devfreq_bw_hwmon_get_freq,
 	.event_handler = devfreq_bw_hwmon_ev_handler,
 };

 int register_bw_hwmon(struct device *dev, struct bw_hwmon *hwmon)
 {
 	int ret = 0;
 	struct hwmon_node *node;
 	struct attribute_group *attr_grp;

 	if (!hwmon->gov && !hwmon->dev && !hwmon->of_node)
 		return -EINVAL;

 	node = devm_kzalloc(dev, sizeof(*node), GFP_KERNEL);
 	if (!node) {
 		dev_err(dev, "Unable to register gov. Out of memory!\n");
 		return -ENOMEM;
 	}

 	if (hwmon->gov) {
 		attr_grp = devm_kzalloc(dev, sizeof(*attr_grp), GFP_KERNEL);
 		if (!attr_grp)
 			return -ENOMEM;

 		hwmon->gov->get_target_freq = devfreq_bw_hwmon_get_freq;
 		hwmon->gov->event_handler = devfreq_bw_hwmon_ev_handler;
 		attr_grp->name = hwmon->gov->name;
 		attr_grp->attrs = dev_attr;

 		node->gov = hwmon->gov;
 		node->attr_grp = attr_grp;
 	} else {
 		node->gov = &devfreq_gov_bw_hwmon;
 		node->attr_grp = &dev_attr_group;
 	}

 	node->tolerance_percent = 10;
 	node->guard_band_mbps = 100;
 	node->decay_rate = 90;
 	node->io_percent = 16;
 	node->bw_step = 190;
 	node->hw = hwmon;

 	mutex_lock(&list_lock);
 	list_add_tail(&node->list, &hwmon_list);
 	mutex_unlock(&list_lock);

 	if (hwmon->gov) {
 		ret = devfreq_add_governor(hwmon->gov);
 	} else {
 		mutex_lock(&state_lock);
 		if (!use_cnt)
 			ret = devfreq_add_governor(&devfreq_gov_bw_hwmon);
 		if (!ret)
 			use_cnt++;
 		mutex_unlock(&state_lock);
 	}

 	if (!ret)
 		dev_info(dev, "BW HWmon governor registered.\n");
 	else
 		dev_err(dev, "BW HWmon governor registration failed!\n");

 	return ret;
 }

 MODULE_DESCRIPTION("HW monitor based dev DDR bandwidth voting driver");
 MODULE_LICENSE("GPL v2");
	/*
	* Copyright (c) 2013-2014, The Linux Foundation. All rights reserved.
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License version 2 and
	* only version 2 as published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*/

	#define pr_fmt(fmt) "bw-hwmon: " fmt

	#include <linux/kernel.h>
	#include <linux/sizes.h>
	#include <linux/module.h>
	#include <linux/init.h>
	#include <linux/io.h>
	#include <linux/delay.h>
	#include <linux/ktime.h>
	#include <linux/time.h>
	#include <linux/err.h>
	#include <linux/errno.h>
	#include <linux/mutex.h>
	#include <linux/interrupt.h>
	#include <linux/platform_device.h>
	#include <linux/of.h>
	#include <linux/devfreq.h>
	#include "governor.h"
	#include "governor_bw_hwmon.h"

	struct hwmon_node {
	unsigned int tolerance_percent;
	unsigned int guard_band_mbps;
	unsigned int decay_rate;
	unsigned int io_percent;
	unsigned int bw_step;
	unsigned long prev_ab;
	unsigned long *dev_ab;
	ktime_t prev_ts;
	bool mon_started;
	struct list_head list;
	void *orig_data;
	struct bw_hwmon *hw;
	struct devfreq_governor *gov;
	struct attribute_group *attr_grp;
	};

	static LIST_HEAD(hwmon_list);
	static DEFINE_MUTEX(list_lock);

	static int use_cnt;
	static DEFINE_MUTEX(state_lock);

	#define show_attr(name) \
	static ssize_t show_##name(struct device *dev, \
	struct device_attribute attr, char buf) \
	{ \
	struct devfreq *df = to_devfreq(dev); \
	struct hwmon_node *hw = df->data; \
	return snprintf(buf, PAGE_SIZE, "%u\n", hw->name); \
	}

	#define store_attr(name, _min, _max) \
	static ssize_t store_##name(struct device *dev, \
	struct device_attribute attr, const char buf, \
	size_t count) \
	{ \
	struct devfreq *df = to_devfreq(dev); \
	struct hwmon_node *hw = df->data; \
	int ret; \
	unsigned int val; \
	ret = sscanf(buf, "%u", &val); \
	if (ret != 1) \
	return -EINVAL; \
	val = max(val, _min); \
	val = min(val, _max); \
	hw->name = val; \
	return count; \
	}

	#define gov_attr(__attr, min, max) \
	show_attr(__attr) \
	store_attr(__attr, min, max) \
	static DEVICE_ATTR(__attr, 0644, show_##__attr, store_##__attr)

	#define MIN_MS 10U
	#define MAX_MS 500U

	static unsigned long measure_bw_and_set_irq(struct hwmon_node *node)
	{
	ktime_t ts;
	unsigned int us;
	unsigned long mbps;
	struct bw_hwmon *hw = node->hw;

	/*
	* Since we are stopping the counters, we don't want this short work
	* to be interrupted by other tasks and cause the measurements to be
	* wrong. Not blocking interrupts to avoid affecting interrupt
	* latency and since they should be short anyway because they run in
	* atomic context.
	*/
	preempt_disable();

	ts = ktime_get();
	us = ktime_to_us(ktime_sub(ts, node->prev_ts));
	if (!us)
	us = 1;

	mbps = hw->meas_bw_and_set_irq(hw, node->tolerance_percent, us);
	node->prev_ts = ts;

	preempt_enable();

	dev_dbg(hw->df->dev.parent, "BW MBps = %6lu, period = %u\n", mbps, us);

	return mbps;
	}

	static void compute_bw(struct hwmon_node *node, int mbps,
	unsigned long freq, unsigned long ab)
	{
	int new_bw;

	mbps += node->guard_band_mbps;

	if (mbps > node->prev_ab) {
	new_bw = mbps;
	} else {
	new_bw = mbps * node->decay_rate
	+ node->prev_ab * (100 - node->decay_rate);
	new_bw /= 100;
	}

	node->prev_ab = new_bw;
	if (ab)
	*ab = roundup(new_bw, node->bw_step);
	freq = (new_bw 100) / node->io_percent;
	}

	static struct hwmon_node find_hwmon_node(struct devfreq df)
	{
	struct hwmon_node node, found = NULL;

	mutex_lock(&list_lock);
	list_for_each_entry(node, &hwmon_list, list)
	if (node->hw->dev == df->dev.parent \|\|
	node->hw->of_node == df->dev.parent->of_node \|\|
	node->gov == df->governor) {
	found = node;
	break;
	}
	mutex_unlock(&list_lock);

	return found;
	}

	#define TOO_SOON_US (1 * USEC_PER_MSEC)
	int update_bw_hwmon(struct bw_hwmon *hwmon)
	{
	struct devfreq *df;
	struct hwmon_node *node;
	ktime_t ts;
	unsigned int us;
	int ret;

	if (!hwmon)
	return -EINVAL;
	df = hwmon->df;
	if (!df)
	return -ENODEV;
	node = find_hwmon_node(df);
	if (!node)
	return -ENODEV;

	if (!node->mon_started)
	return -EBUSY;

	dev_dbg(df->dev.parent, "Got update request\n");
	devfreq_monitor_stop(df);

	/*
	* Don't recalc bandwidth if the interrupt comes right after a
	* previous bandwidth calculation. This is done for two reasons:
	*
	* 1. Sampling the BW during a very short duration can result in a
	* very inaccurate measurement due to very short bursts.
	* 2. This can only happen if the limit was hit very close to the end
	* of the previous sample period. Which means the current BW
	* estimate is not very off and doesn't need to be readjusted.
	*/
	ts = ktime_get();
	us = ktime_to_us(ktime_sub(ts, node->prev_ts));
	if (us > TOO_SOON_US) {
	mutex_lock(&df->lock);
	ret = update_devfreq(df);
	if (ret)
	dev_err(df->dev.parent,
	"Unable to update freq on request!\n");
	mutex_unlock(&df->lock);
	}

	devfreq_monitor_start(df);

	return 0;
	}

	static int start_monitoring(struct devfreq *df)
	{
	int ret = 0;
	unsigned long mbps;
	struct device *dev = df->dev.parent;
	struct hwmon_node *node;
	struct bw_hwmon *hw;
	struct devfreq_dev_status stat;

	node = find_hwmon_node(df);
	if (!node) {
	dev_err(dev, "Unable to find HW monitor!\n");
	return -ENODEV;
	}
	hw = node->hw;

	stat.private_data = NULL;
	if (df->profile->get_dev_status)
	ret = df->profile->get_dev_status(df->dev.parent, &stat);
	if (ret \|\| !stat.private_data)
	dev_warn(dev, "Device doesn't take AB votes!\n");
	else
	node->dev_ab = stat.private_data;

	hw->df = df;
	node->orig_data = df->data;
	df->data = node;

	node->prev_ts = ktime_get();
	node->prev_ab = 0;
	mbps = (df->previous_freq * node->io_percent) / 100;
	ret = hw->start_hwmon(hw, mbps);
	if (ret) {
	dev_err(dev, "Unable to start HW monitor!\n");
	goto err_start;
	}

	devfreq_monitor_start(df);
	node->mon_started = true;

	ret = sysfs_create_group(&df->dev.kobj, node->attr_grp);
	if (ret)
	goto err_sysfs;

	return 0;

	err_sysfs:
	node->mon_started = false;
	devfreq_monitor_stop(df);
	hw->stop_hwmon(hw);
	err_start:
	df->data = node->orig_data;
	node->orig_data = NULL;
	hw->df = NULL;
	node->dev_ab = NULL;
	return ret;
	}

	static void stop_monitoring(struct devfreq *df)
	{
	struct hwmon_node *node = df->data;
	struct bw_hwmon *hw = node->hw;

	sysfs_remove_group(&df->dev.kobj, node->attr_grp);
	node->mon_started = false;
	devfreq_monitor_stop(df);
	hw->stop_hwmon(hw);
	df->data = node->orig_data;
	node->orig_data = NULL;
	hw->df = NULL;
	/*
	* Not all governors know about this additional extended device
	* configuration. To avoid leaving the extended configuration at a
	* stale state, set it to 0 and let the next governor take it from
	* there.
	*/
	if (node->dev_ab)
	*node->dev_ab = 0;
	node->dev_ab = NULL;
	}

	static int devfreq_bw_hwmon_get_freq(struct devfreq *df,
	unsigned long *freq,
	u32 *flag)
	{
	unsigned long mbps;
	struct hwmon_node *node = df->data;

	mbps = measure_bw_and_set_irq(node);
	compute_bw(node, mbps, freq, node->dev_ab);

	return 0;
	}

	gov_attr(tolerance_percent, 0U, 30U);
	gov_attr(guard_band_mbps, 0U, 2000U);
	gov_attr(decay_rate, 0U, 100U);
	gov_attr(io_percent, 1U, 100U);
	gov_attr(bw_step, 50U, 1000U);

	static struct attribute *dev_attr[] = {
	&dev_attr_tolerance_percent.attr,
	&dev_attr_guard_band_mbps.attr,
	&dev_attr_decay_rate.attr,
	&dev_attr_io_percent.attr,
	&dev_attr_bw_step.attr,
	NULL,
	};

	static struct attribute_group dev_attr_group = {
	.name = "bw_hwmon",
	.attrs = dev_attr,
	};

	static int devfreq_bw_hwmon_ev_handler(struct devfreq *df,
	unsigned int event, void *data)
	{
	int ret;
	unsigned int sample_ms;

	switch (event) {
	case DEVFREQ_GOV_START:
	sample_ms = df->profile->polling_ms;
	sample_ms = max(MIN_MS, sample_ms);
	sample_ms = min(MAX_MS, sample_ms);
	df->profile->polling_ms = sample_ms;

	ret = start_monitoring(df);
	if (ret)
	return ret;

	dev_dbg(df->dev.parent,
	"Enabled dev BW HW monitor governor\n");
	break;

	case DEVFREQ_GOV_STOP:
	stop_monitoring(df);
	dev_dbg(df->dev.parent,
	"Disabled dev BW HW monitor governor\n");
	break;

	case DEVFREQ_GOV_INTERVAL:
	sample_ms = (unsigned int )data;
	sample_ms = max(MIN_MS, sample_ms);
	sample_ms = min(MAX_MS, sample_ms);
	devfreq_interval_update(df, &sample_ms);
	break;
	}

	return 0;
	}

	static struct devfreq_governor devfreq_gov_bw_hwmon = {
	.name = "bw_hwmon",
	.get_target_freq = devfreq_bw_hwmon_get_freq,
	.event_handler = devfreq_bw_hwmon_ev_handler,
	};

	int register_bw_hwmon(struct device dev, struct bw_hwmon hwmon)
	{
	int ret = 0;
	struct hwmon_node *node;
	struct attribute_group *attr_grp;

	if (!hwmon->gov && !hwmon->dev && !hwmon->of_node)
	return -EINVAL;

	node = devm_kzalloc(dev, sizeof(*node), GFP_KERNEL);
	if (!node) {
	dev_err(dev, "Unable to register gov. Out of memory!\n");
	return -ENOMEM;
	}

	if (hwmon->gov) {
	attr_grp = devm_kzalloc(dev, sizeof(*attr_grp), GFP_KERNEL);
	if (!attr_grp)
	return -ENOMEM;

	hwmon->gov->get_target_freq = devfreq_bw_hwmon_get_freq;
	hwmon->gov->event_handler = devfreq_bw_hwmon_ev_handler;
	attr_grp->name = hwmon->gov->name;
	attr_grp->attrs = dev_attr;

	node->gov = hwmon->gov;
	node->attr_grp = attr_grp;
	} else {
	node->gov = &devfreq_gov_bw_hwmon;
	node->attr_grp = &dev_attr_group;
	}

	node->tolerance_percent = 10;
	node->guard_band_mbps = 100;
	node->decay_rate = 90;
	node->io_percent = 16;
	node->bw_step = 190;
	node->hw = hwmon;

	mutex_lock(&list_lock);
	list_add_tail(&node->list, &hwmon_list);
	mutex_unlock(&list_lock);

	if (hwmon->gov) {
	ret = devfreq_add_governor(hwmon->gov);
	} else {
	mutex_lock(&state_lock);
	if (!use_cnt)
	ret = devfreq_add_governor(&devfreq_gov_bw_hwmon);
	if (!ret)
	use_cnt++;
	mutex_unlock(&state_lock);
	}

	if (!ret)
	dev_info(dev, "BW HWmon governor registered.\n");
	else
	dev_err(dev, "BW HWmon governor registration failed!\n");

	return ret;
	}

	MODULE_DESCRIPTION("HW monitor based dev DDR bandwidth voting driver");
	MODULE_LICENSE("GPL v2");