[2/2] PM / devfreq: Generic cpufreq governor

This devfreq governor is a generic implementation that can scale any
devfreq device based on the current CPU frequency of all ONLINE CPUs. It
allows for specifying CPU freq to devfreq mapping for specific devices.
When such a mapping is not present, it defaults to scaling the device
frequency in proportion to the CPU frequency.

Change-Id: I7f786b9059435afe85b9ec8c504a4655731ee20e
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
---
 .../bindings/devfreq/devfreq-cpufreq.txt           |  53 ++
 drivers/devfreq/Kconfig                            |   8 +
 drivers/devfreq/Makefile                           |   1 +
 drivers/devfreq/governor_cpufreq.c                 | 628 +++++++++++++++++++++
 4 files changed, 690 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/devfreq/devfreq-cpufreq.txt
 create mode 100644 drivers/devfreq/governor_cpufreq.c

On Fri, May 18, 2018 at 01:24:48AM -0700, Saravana Kannan wrote:
> This devfreq governor is a generic implementation that can scale any
> devfreq device based on the current CPU frequency of all ONLINE CPUs. It
> allows for specifying CPU freq to devfreq mapping for specific devices.
> When such a mapping is not present, it defaults to scaling the device
> frequency in proportion to the CPU frequency.
> 
> Change-Id: I7f786b9059435afe85b9ec8c504a4655731ee20e

drop this.

> Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
> ---
>  .../bindings/devfreq/devfreq-cpufreq.txt           |  53 ++

Please split bindings to separate patch.

>  drivers/devfreq/Kconfig                            |   8 +
>  drivers/devfreq/Makefile                           |   1 +
>  drivers/devfreq/governor_cpufreq.c                 | 628 +++++++++++++++++++++
>  4 files changed, 690 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/devfreq/devfreq-cpufreq.txt
>  create mode 100644 drivers/devfreq/governor_cpufreq.c
> 
> diff --git a/Documentation/devicetree/bindings/devfreq/devfreq-cpufreq.txt b/Documentation/devicetree/bindings/devfreq/devfreq-cpufreq.txt
> new file mode 100644
> index 0000000..6537538
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/devfreq/devfreq-cpufreq.txt
> @@ -0,0 +1,53 @@
> +Devfreq CPUfreq governor
> +
> +devfreq-cpufreq is a parent device that contains one or more child devices.
> +Each child device provides CPU frequency to device frequency mapping for a
> +specific device. Examples of devices that could use this are: DDR, cache and
> +CCI.
> +
> +Parent device name shall be "devfreq-cpufreq".

I don't really understand any of this and how it relates to the other 
QCom cpufreq and devfreq bindings. Seems like this all needs some 
discussion amongst the PM folks first.

Rob
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>Many CPU architectures have caches that can scale independent of the CPUs.
>Frequency scaling of the caches is necessary to make sure the cache is not
>a performance bottleneck that leads to poor performance and power. The same
>idea applies for RAM/DDR.
>
>To achieve this, this patch series adds a generic devfreq governor that can
>listen to the frequency transitions of each CPU frequency domain and then
>adjusts the frequency of the cache (or any devfreq device) based on the
>frequency of the CPUs.

I agree that we have some hardware pieces that want to configure
frequencies based on the CPUfreq.

Creating a devfreq governor that configures devfreq-freq
based on incoming events (CPUFreq-transition-event in this case)
is indeed a good idea.

However, I would like to ask the followings:
The overall code appears to be overly complex compared what you need.
- Do you really need to revive "CPUFREQ POLICY" events for this?
especially when you are going to look at "first CPU" only?


Cheers,
MyungJoo

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Chanwoo,

Friendly reminder for a review. I've addressed your comments on v1 of 
this patch.

-Saravana


On 05/18/2018 01:24 AM, Saravana Kannan wrote:
> This devfreq governor is a generic implementation that can scale any
> devfreq device based on the current CPU frequency of all ONLINE CPUs. It
> allows for specifying CPU freq to devfreq mapping for specific devices.
> When such a mapping is not present, it defaults to scaling the device
> frequency in proportion to the CPU frequency.
>
> Change-Id: I7f786b9059435afe85b9ec8c504a4655731ee20e
> Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
> ---
>   .../bindings/devfreq/devfreq-cpufreq.txt           |  53 ++
>   drivers/devfreq/Kconfig                            |   8 +
>   drivers/devfreq/Makefile                           |   1 +
>   drivers/devfreq/governor_cpufreq.c                 | 628 +++++++++++++++++++++
>   4 files changed, 690 insertions(+)
>   create mode 100644 Documentation/devicetree/bindings/devfreq/devfreq-cpufreq.txt
>   create mode 100644 drivers/devfreq/governor_cpufreq.c
>
> diff --git a/Documentation/devicetree/bindings/devfreq/devfreq-cpufreq.txt b/Documentation/devicetree/bindings/devfreq/devfreq-cpufreq.txt
> new file mode 100644
> index 0000000..6537538
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/devfreq/devfreq-cpufreq.txt
> @@ -0,0 +1,53 @@
> +Devfreq CPUfreq governor
> +
> +devfreq-cpufreq is a parent device that contains one or more child devices.
> +Each child device provides CPU frequency to device frequency mapping for a
> +specific device. Examples of devices that could use this are: DDR, cache and
> +CCI.
> +
> +Parent device name shall be "devfreq-cpufreq".
> +
> +Required child device properties:
> +- cpu-to-dev-map, or cpu-to-dev-map-<X>:
> +			A list of tuples where each tuple consists of a
> +			CPU frequency (KHz) and the corresponding device
> +			frequency. CPU frequencies not listed in the table
> +			will use the device frequency that corresponds to the
> +			next rounded up CPU frequency.
> +			Use "cpu-to-dev-map" if all CPUs in the system should
> +			share same mapping.
> +			Use cpu-to-dev-map-<cpuid> to describe different
> +			mappings for different CPUs. The property should be
> +			listed only for the first CPU if multiple CPUs are
> +			synchronous.
> +- target-dev:		Phandle to device that this mapping applies to.
> +
> +Example:
> +	devfreq-cpufreq {
> +		cpubw-cpufreq {
> +			target-dev = <&cpubw>;
> +			cpu-to-dev-map =
> +				<  300000  1144 >,
> +				<  422400  2288 >,
> +				<  652800  3051 >,
> +				<  883200  5996 >,
> +				< 1190400  8056 >,
> +				< 1497600 10101 >,
> +				< 1728000 12145 >,
> +				< 2649600 16250 >;
> +		};
> +
> +		cache-cpufreq {
> +			target-dev = <&cache>;
> +			cpu-to-dev-map =
> +				<  300000  300000 >,
> +				<  422400  422400 >,
> +				<  652800  499200 >,
> +				<  883200  576000 >,
> +				<  960000  960000 >,
> +				< 1497600 1036800 >,
> +				< 1574400 1574400 >,
> +				< 1728000 1651200 >,
> +				< 2649600 1728000 >;
> +		};
> +	};
> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
> index 8503018..5eeb33f 100644
> --- a/drivers/devfreq/Kconfig
> +++ b/drivers/devfreq/Kconfig
> @@ -73,6 +73,14 @@ config DEVFREQ_GOV_PASSIVE
>   	  through sysfs entries. The passive governor recommends that
>   	  devfreq device uses the OPP table to get the frequency/voltage.
>   
> +config DEVFREQ_GOV_CPUFREQ
> +	tristate "CPUfreq"
> +	depends on CPU_FREQ
> +	help
> +	  Chooses frequency based on the online CPUs' current frequency and a
> +	  CPU frequency to device frequency mapping table(s). This governor
> +	  can be useful for controlling devices such as DDR, cache, CCI, etc.
> +
>   comment "DEVFREQ Drivers"
>   
>   config ARM_EXYNOS_BUS_DEVFREQ
> diff --git a/drivers/devfreq/Makefile b/drivers/devfreq/Makefile
> index f1cc8990..cafe7c2 100644
> --- a/drivers/devfreq/Makefile
> +++ b/drivers/devfreq/Makefile
> @@ -6,6 +6,7 @@ obj-$(CONFIG_DEVFREQ_GOV_PERFORMANCE)	+= governor_performance.o
>   obj-$(CONFIG_DEVFREQ_GOV_POWERSAVE)	+= governor_powersave.o
>   obj-$(CONFIG_DEVFREQ_GOV_USERSPACE)	+= governor_userspace.o
>   obj-$(CONFIG_DEVFREQ_GOV_PASSIVE)	+= governor_passive.o
> +obj-$(CONFIG_DEVFREQ_GOV_CPUFREQ)	+= governor_cpufreq.o
>   
>   # DEVFREQ Drivers
>   obj-$(CONFIG_ARM_EXYNOS_BUS_DEVFREQ)	+= exynos-bus.o
> diff --git a/drivers/devfreq/governor_cpufreq.c b/drivers/devfreq/governor_cpufreq.c
> new file mode 100644
> index 0000000..8f8ea26
> --- /dev/null
> +++ b/drivers/devfreq/governor_cpufreq.c
> @@ -0,0 +1,628 @@
> +/*
> + * Copyright (c) 2014-2015, 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) "dev-cpufreq: " fmt
> +
> +#include <linux/devfreq.h>
> +#include <linux/cpu.h>
> +#include <linux/cpufreq.h>
> +#include <linux/cpumask.h>
> +#include <linux/slab.h>
> +#include <linux/platform_device.h>
> +#include <linux/of.h>
> +#include <linux/module.h>
> +#include "governor.h"
> +
> +struct cpu_state {
> +	unsigned int freq;
> +	unsigned int min_freq;
> +	unsigned int max_freq;
> +	bool on;
> +	unsigned int first_cpu;
> +};
> +static struct cpu_state *state[NR_CPUS];
> +static int cpufreq_cnt;
> +
> +struct freq_map {
> +	unsigned int cpu_khz;
> +	unsigned int target_freq;
> +};
> +
> +struct devfreq_node {
> +	struct devfreq *df;
> +	void *orig_data;
> +	struct device *dev;
> +	struct device_node *of_node;
> +	struct list_head list;
> +	struct freq_map **map;
> +	struct freq_map *common_map;
> +};
> +static LIST_HEAD(devfreq_list);
> +static DEFINE_MUTEX(state_lock);
> +static DEFINE_MUTEX(cpufreq_reg_lock);
> +
> +static void update_all_devfreqs(void)
> +{
> +	struct devfreq_node *node;
> +
> +	list_for_each_entry(node, &devfreq_list, list) {
> +		struct devfreq *df = node->df;
> +		if (!node->df)
> +			continue;
> +		mutex_lock(&df->lock);
> +		update_devfreq(df);
> +		mutex_unlock(&df->lock);
> +
> +	}
> +}
> +
> +static struct devfreq_node *find_devfreq_node(struct device *dev)
> +{
> +	struct devfreq_node *node;
> +
> +	list_for_each_entry(node, &devfreq_list, list)
> +		if (node->dev == dev || node->of_node == dev->of_node)
> +			return node;
> +
> +	return NULL;
> +}
> +
> +/* ==================== cpufreq part ==================== */
> +static void add_policy(struct cpufreq_policy *policy)
> +{
> +	struct cpu_state *new_state;
> +	unsigned int cpu, first_cpu;
> +
> +	if (state[policy->cpu]) {
> +		state[policy->cpu]->freq = policy->cur;
> +		state[policy->cpu]->on = true;
> +	} else {
> +		new_state = kzalloc(sizeof(struct cpu_state), GFP_KERNEL);
> +		if (!new_state)
> +			return;
> +
> +		first_cpu = cpumask_first(policy->related_cpus);
> +		new_state->first_cpu = first_cpu;
> +		new_state->freq = policy->cur;
> +		new_state->min_freq = policy->cpuinfo.min_freq;
> +		new_state->max_freq = policy->cpuinfo.max_freq;
> +		new_state->on = true;
> +
> +		for_each_cpu(cpu, policy->related_cpus)
> +			state[cpu] = new_state;
> +	}
> +}
> +
> +static int cpufreq_policy_notifier(struct notifier_block *nb,
> +		unsigned long event, void *data)
> +{
> +	struct cpufreq_policy *policy = data;
> +
> +	switch (event) {
> +	case CPUFREQ_CREATE_POLICY:
> +		mutex_lock(&state_lock);
> +		add_policy(policy);
> +		update_all_devfreqs();
> +		mutex_unlock(&state_lock);
> +		break;
> +
> +	case CPUFREQ_REMOVE_POLICY:
> +		mutex_lock(&state_lock);
> +		if (state[policy->cpu]) {
> +			state[policy->cpu]->on = false;
> +			update_all_devfreqs();
> +		}
> +		mutex_unlock(&state_lock);
> +		break;
> +	}
> +
> +	return 0;
> +}
> +
> +static struct notifier_block cpufreq_policy_nb = {
> +	.notifier_call = cpufreq_policy_notifier
> +};
> +
> +static int cpufreq_trans_notifier(struct notifier_block *nb,
> +		unsigned long event, void *data)
> +{
> +	struct cpufreq_freqs *freq = data;
> +	struct cpu_state *s;
> +
> +	if (event != CPUFREQ_POSTCHANGE)
> +		return 0;
> +
> +	mutex_lock(&state_lock);
> +
> +	s = state[freq->cpu];
> +	if (!s)
> +		goto out;
> +
> +	if (s->freq != freq->new) {
> +		s->freq = freq->new;
> +		update_all_devfreqs();
> +	}
> +
> +out:
> +	mutex_unlock(&state_lock);
> +	return 0;
> +}
> +
> +static struct notifier_block cpufreq_trans_nb = {
> +	.notifier_call = cpufreq_trans_notifier
> +};
> +
> +static int register_cpufreq(void)
> +{
> +	int ret = 0;
> +	unsigned int cpu;
> +	struct cpufreq_policy *policy;
> +
> +	mutex_lock(&cpufreq_reg_lock);
> +
> +	if (cpufreq_cnt)
> +		goto cnt_not_zero;
> +
> +	get_online_cpus();
> +	ret = cpufreq_register_notifier(&cpufreq_policy_nb,
> +				CPUFREQ_POLICY_NOTIFIER);
> +	if (ret)
> +		goto out;
> +
> +	ret = cpufreq_register_notifier(&cpufreq_trans_nb,
> +				CPUFREQ_TRANSITION_NOTIFIER);
> +	if (ret) {
> +		cpufreq_unregister_notifier(&cpufreq_policy_nb,
> +				CPUFREQ_POLICY_NOTIFIER);
> +		goto out;
> +	}
> +
> +	for_each_online_cpu(cpu) {
> +		policy = cpufreq_cpu_get(cpu);
> +		if (policy) {
> +			add_policy(policy);
> +			cpufreq_cpu_put(policy);
> +		}
> +	}
> +out:
> +	put_online_cpus();
> +cnt_not_zero:
> +	if (!ret)
> +		cpufreq_cnt++;
> +	mutex_unlock(&cpufreq_reg_lock);
> +	return ret;
> +}
> +
> +static int unregister_cpufreq(void)
> +{
> +	int ret = 0;
> +	int cpu;
> +
> +	mutex_lock(&cpufreq_reg_lock);
> +
> +	if (cpufreq_cnt > 1)
> +		goto out;
> +
> +	cpufreq_unregister_notifier(&cpufreq_policy_nb,
> +				CPUFREQ_POLICY_NOTIFIER);
> +	cpufreq_unregister_notifier(&cpufreq_trans_nb,
> +				CPUFREQ_TRANSITION_NOTIFIER);
> +
> +	for (cpu = ARRAY_SIZE(state) - 1; cpu >= 0; cpu--) {
> +		if (!state[cpu])
> +			continue;
> +		if (state[cpu]->first_cpu == cpu)
> +			kfree(state[cpu]);
> +		state[cpu] = NULL;
> +	}
> +
> +out:
> +	cpufreq_cnt--;
> +	mutex_unlock(&cpufreq_reg_lock);
> +	return ret;
> +}
> +
> +/* ==================== devfreq part ==================== */
> +
> +static unsigned int interpolate_freq(struct devfreq *df, unsigned int cpu)
> +{
> +	unsigned long *freq_table = df->profile->freq_table;
> +	unsigned int cpu_min = state[cpu]->min_freq;
> +	unsigned int cpu_max = state[cpu]->max_freq;
> +	unsigned int cpu_freq = state[cpu]->freq;
> +	unsigned int dev_min, dev_max, cpu_percent;
> +
> +	if (freq_table) {
> +		dev_min = freq_table[0];
> +		dev_max = freq_table[df->profile->max_state - 1];
> +	} else {
> +		if (df->max_freq <= df->min_freq)
> +			return 0;
> +		dev_min = df->min_freq;
> +		dev_max = df->max_freq;
> +	}
> +
> +	cpu_percent = ((cpu_freq - cpu_min) * 100) / (cpu_max - cpu_min);
> +	return dev_min + mult_frac(dev_max - dev_min, cpu_percent, 100);
> +}
> +
> +static unsigned int cpu_to_dev_freq(struct devfreq *df, unsigned int cpu)
> +{
> +	struct freq_map *map = NULL;
> +	unsigned int cpu_khz = 0, freq;
> +	struct devfreq_node *n = df->data;
> +
> +	if (!state[cpu] || !state[cpu]->on || state[cpu]->first_cpu != cpu) {
> +		freq = 0;
> +		goto out;
> +	}
> +
> +	if (n->common_map)
> +		map = n->common_map;
> +	else if (n->map)
> +		map = n->map[cpu];
> +
> +	cpu_khz = state[cpu]->freq;
> +
> +	if (!map) {
> +		freq = interpolate_freq(df, cpu);
> +		goto out;
> +	}
> +
> +	while (map->cpu_khz && map->cpu_khz < cpu_khz)
> +		map++;
> +	if (!map->cpu_khz)
> +		map--;
> +	freq = map->target_freq;
> +
> +out:
> +	dev_dbg(df->dev.parent, "CPU%u: %d -> dev: %u\n", cpu, cpu_khz, freq);
> +	return freq;
> +}
> +
> +static int devfreq_cpufreq_get_freq(struct devfreq *df,
> +					unsigned long *freq)
> +{
> +	unsigned int cpu, tgt_freq = 0;
> +	struct devfreq_node *node;
> +
> +	node = df->data;
> +	if (!node) {
> +		pr_err("Unable to find devfreq node!\n");
> +		return -ENODEV;
> +	}
> +
> +	for_each_possible_cpu(cpu)
> +		tgt_freq = max(tgt_freq, cpu_to_dev_freq(df, cpu));
> +
> +	*freq = tgt_freq;
> +	return 0;
> +}
> +
> +static unsigned int show_table(char *buf, unsigned int len,
> +				struct freq_map *map)
> +{
> +	unsigned int cnt = 0;
> +
> +	cnt += snprintf(buf + cnt, len - cnt, "CPU freq\tDevice freq\n");
> +
> +	while (map->cpu_khz && cnt < len) {
> +		cnt += snprintf(buf + cnt, len - cnt, "%8u\t%11u\n",
> +				map->cpu_khz, map->target_freq);
> +		map++;
> +	}
> +	if (cnt < len)
> +		cnt += snprintf(buf + cnt, len - cnt, "\n");
> +
> +	return cnt;
> +}
> +
> +static ssize_t show_map(struct device *dev, struct device_attribute *attr,
> +			char *buf)
> +{
> +	struct devfreq *df = to_devfreq(dev);
> +	struct devfreq_node *n = df->data;
> +	struct freq_map *map;
> +	unsigned int cnt = 0, cpu;
> +
> +	mutex_lock(&state_lock);
> +	if (n->common_map) {
> +		map = n->common_map;
> +		cnt += snprintf(buf + cnt, PAGE_SIZE - cnt,
> +				"Common table for all CPUs:\n");
> +		cnt += show_table(buf + cnt, PAGE_SIZE - cnt, map);
> +	} else if (n->map) {
> +		for_each_possible_cpu(cpu) {
> +			map = n->map[cpu];
> +			if (!map)
> +				continue;
> +			cnt += snprintf(buf + cnt, PAGE_SIZE - cnt,
> +					"CPU %u:\n", cpu);
> +			if (cnt >= PAGE_SIZE)
> +				break;
> +			cnt += show_table(buf + cnt, PAGE_SIZE - cnt, map);
> +			if (cnt >= PAGE_SIZE)
> +				break;
> +		}
> +	} else {
> +		cnt += snprintf(buf + cnt, PAGE_SIZE - cnt,
> +				"Device freq interpolated based on CPU freq\n");
> +	}
> +	mutex_unlock(&state_lock);
> +
> +	return cnt;
> +}
> +
> +static DEVICE_ATTR(freq_map, 0444, show_map, NULL);
> +static struct attribute *dev_attr[] = {
> +	&dev_attr_freq_map.attr,
> +	NULL,
> +};
> +
> +static struct attribute_group dev_attr_group = {
> +	.name = "cpufreq",
> +	.attrs = dev_attr,
> +};
> +
> +static int devfreq_cpufreq_gov_start(struct devfreq *devfreq)
> +{
> +	int ret = 0;
> +	struct devfreq_node *node;
> +	bool alloc = false;
> +
> +	ret = register_cpufreq();
> +	if (ret)
> +		return ret;
> +
> +	ret = sysfs_create_group(&devfreq->dev.kobj, &dev_attr_group);
> +	if (ret) {
> +		unregister_cpufreq();
> +		return ret;
> +	}
> +
> +	mutex_lock(&state_lock);
> +
> +	node = find_devfreq_node(devfreq->dev.parent);
> +	if (node == NULL) {
> +		node = kzalloc(sizeof(struct devfreq_node), GFP_KERNEL);
> +		if (!node) {
> +			pr_err("Out of memory!\n");
> +			ret = -ENOMEM;
> +			goto alloc_fail;
> +		}
> +		alloc = true;
> +		node->dev = devfreq->dev.parent;
> +		list_add_tail(&node->list, &devfreq_list);
> +	}
> +	node->df = devfreq;
> +	node->orig_data = devfreq->data;
> +	devfreq->data = node;
> +
> +	mutex_lock(&devfreq->lock);
> +	ret = update_devfreq(devfreq);
> +	mutex_unlock(&devfreq->lock);
> +	if (ret) {
> +		pr_err("Freq update failed!\n");
> +		goto update_fail;
> +	}
> +
> +	mutex_unlock(&state_lock);
> +	return 0;
> +
> +update_fail:
> +	devfreq->data = node->orig_data;
> +	if (alloc) {
> +		list_del(&node->list);
> +		kfree(node);
> +	}
> +alloc_fail:
> +	mutex_unlock(&state_lock);
> +	sysfs_remove_group(&devfreq->dev.kobj, &dev_attr_group);
> +	unregister_cpufreq();
> +	return ret;
> +}
> +
> +static void devfreq_cpufreq_gov_stop(struct devfreq *devfreq)
> +{
> +	struct devfreq_node *node = devfreq->data;
> +
> +	mutex_lock(&state_lock);
> +	devfreq->data = node->orig_data;
> +	if (node->map || node->common_map) {
> +		node->df = NULL;
> +	} else {
> +		list_del(&node->list);
> +		kfree(node);
> +	}
> +	mutex_unlock(&state_lock);
> +
> +	sysfs_remove_group(&devfreq->dev.kobj, &dev_attr_group);
> +	unregister_cpufreq();
> +}
> +
> +static int devfreq_cpufreq_ev_handler(struct devfreq *devfreq,
> +					unsigned int event, void *data)
> +{
> +	int ret;
> +
> +	switch (event) {
> +	case DEVFREQ_GOV_START:
> +
> +		ret = devfreq_cpufreq_gov_start(devfreq);
> +		if (ret) {
> +			pr_err("Governor start failed!\n");
> +			return ret;
> +		}
> +		pr_debug("Enabled dev CPUfreq governor\n");
> +		break;
> +
> +	case DEVFREQ_GOV_STOP:
> +
> +		devfreq_cpufreq_gov_stop(devfreq);
> +		pr_debug("Disabled dev CPUfreq governor\n");
> +		break;
> +	}
> +
> +	return 0;
> +}
> +
> +static struct devfreq_governor devfreq_cpufreq = {
> +	.name = "cpufreq",
> +	.get_target_freq = devfreq_cpufreq_get_freq,
> +	.event_handler = devfreq_cpufreq_ev_handler,
> +};
> +
> +#define NUM_COLS	2
> +static struct freq_map *read_tbl(struct device_node *of_node, char *prop_name)
> +{
> +	int len, nf, i, j;
> +	u32 data;
> +	struct freq_map *tbl;
> +
> +	if (!of_find_property(of_node, prop_name, &len))
> +		return NULL;
> +	len /= sizeof(data);
> +
> +	if (len % NUM_COLS || len == 0)
> +		return NULL;
> +	nf = len / NUM_COLS;
> +
> +	tbl = kzalloc((nf + 1) * sizeof(*tbl), GFP_KERNEL);
> +	if (!tbl)
> +		return NULL;
> +
> +	for (i = 0, j = 0; i < nf; i++, j += 2) {
> +		of_property_read_u32_index(of_node, prop_name, j, &data);
> +		tbl[i].cpu_khz = data;
> +
> +		of_property_read_u32_index(of_node, prop_name, j + 1, &data);
> +		tbl[i].target_freq = data;
> +	}
> +	tbl[i].cpu_khz = 0;
> +
> +	return tbl;
> +}
> +
> +#define PROP_TARGET "target-dev"
> +#define PROP_TABLE "cpu-to-dev-map"
> +static int add_table_from_of(struct device_node *of_node)
> +{
> +	struct device_node *target_of_node;
> +	struct devfreq_node *node;
> +	struct freq_map *common_tbl;
> +	struct freq_map **tbl_list = NULL;
> +	static char prop_name[] = PROP_TABLE "-999999";
> +	int cpu, ret, cnt = 0, prop_sz = ARRAY_SIZE(prop_name);
> +
> +	target_of_node = of_parse_phandle(of_node, PROP_TARGET, 0);
> +	if (!target_of_node)
> +		return -EINVAL;
> +
> +	node = kzalloc(sizeof(struct devfreq_node), GFP_KERNEL);
> +	if (!node)
> +		return -ENOMEM;
> +
> +	common_tbl = read_tbl(of_node, PROP_TABLE);
> +	if (!common_tbl) {
> +		tbl_list = kzalloc(sizeof(*tbl_list) * NR_CPUS, GFP_KERNEL);
> +		if (!tbl_list) {
> +			ret = -ENOMEM;
> +			goto err_list;
> +		}
> +
> +		for_each_possible_cpu(cpu) {
> +			ret = snprintf(prop_name, prop_sz, "%s-%d",
> +					PROP_TABLE, cpu);
> +			if (ret >= prop_sz) {
> +				pr_warn("More CPUs than I can handle!\n");
> +				pr_warn("Skipping rest of the tables!\n");
> +				break;
> +			}
> +			tbl_list[cpu] = read_tbl(of_node, prop_name);
> +			if (tbl_list[cpu])
> +				cnt++;
> +		}
> +	}
> +	if (!common_tbl && !cnt) {
> +		ret = -EINVAL;
> +		goto err_tbl;
> +	}
> +
> +	mutex_lock(&state_lock);
> +	node->of_node = target_of_node;
> +	node->map = tbl_list;
> +	node->common_map = common_tbl;
> +	list_add_tail(&node->list, &devfreq_list);
> +	mutex_unlock(&state_lock);
> +
> +	return 0;
> +err_tbl:
> +	kfree(tbl_list);
> +err_list:
> +	kfree(node);
> +	return ret;
> +}
> +
> +static int __init devfreq_cpufreq_init(void)
> +{
> +	int ret;
> +	struct device_node *of_par, *of_child;
> +
> +	of_par = of_find_node_by_name(NULL, "devfreq-cpufreq");
> +	if (of_par) {
> +		for_each_child_of_node(of_par, of_child) {
> +			ret = add_table_from_of(of_child);
> +			if (ret)
> +				pr_err("Parsing %s failed!\n", of_child->name);
> +			else
> +				pr_debug("Parsed %s.\n", of_child->name);
> +		}
> +		of_node_put(of_par);
> +	} else {
> +		pr_info("No tables parsed from DT.\n");
> +	}
> +
> +	ret = devfreq_add_governor(&devfreq_cpufreq);
> +	if (ret) {
> +		pr_err("Governor add failed!\n");
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +subsys_initcall(devfreq_cpufreq_init);
> +
> +static void __exit devfreq_cpufreq_exit(void)
> +{
> +	int ret, cpu;
> +	struct devfreq_node *node, *tmp;
> +
> +	ret = devfreq_remove_governor(&devfreq_cpufreq);
> +	if (ret)
> +		pr_err("Governor remove failed!\n");
> +
> +	mutex_lock(&state_lock);
> +	list_for_each_entry_safe(node, tmp, &devfreq_list, list) {
> +		kfree(node->common_map);
> +		for_each_possible_cpu(cpu)
> +			kfree(node->map[cpu]);
> +		kfree(node->map);
> +		list_del(&node->list);
> +		kfree(node);
> +	}
> +	mutex_unlock(&state_lock);
> +}
> +module_exit(devfreq_cpufreq_exit);
> +
> +MODULE_DESCRIPTION("CPU freq based generic governor for devfreq devices");
> +MODULE_LICENSE("GPL v2");

On 05/27/2018 11:00 PM, MyungJoo Ham wrote:
>> Many CPU architectures have caches that can scale independent of the CPUs.
>> Frequency scaling of the caches is necessary to make sure the cache is not
>> a performance bottleneck that leads to poor performance and power. The same
>> idea applies for RAM/DDR.
>>
>> To achieve this, this patch series adds a generic devfreq governor that can
>> listen to the frequency transitions of each CPU frequency domain and then
>> adjusts the frequency of the cache (or any devfreq device) based on the
>> frequency of the CPUs.
> I agree that we have some hardware pieces that want to configure
> frequencies based on the CPUfreq.
>
> Creating a devfreq governor that configures devfreq-freq
> based on incoming events (CPUFreq-transition-event in this case)
> is indeed a good idea.
>
> However, I would like to ask the followings:
> The overall code appears to be overly complex compared what you need.
> - Do you really need to revive "CPUFREQ POLICY" events for this?
> especially when you are going to look at "first CPU" only?
>
>
> Cheers,
> MyungJoo
>
Sorry, didn't notice this email earlier. My message filters seem to be 
messed up.

The POLICY notifiers are necessary for cases when all CPUs in a policy 
are hotplugged off -- we need to ignore their frequencies to avoid 
getting the devfreq device stuck at a high frequency. Looking at "first 
CPU" is just an optimization to ignore multiple transition notifiers for 
the each CPU in a policy -- we'd want to do that even if we don't have 
policy notifiers. Not having policy notifier won't really simplify the 
code by much. We'd be forced to check for policy->related_cpus for every 
transition notifier call if the CPU state hasn't been already initialized.

-Saravana