Re: [PATCH v8 5/6] PM / devfreq: Add PM QoS support

[Leonard Crestez <leonard.crestez@nxp.com>]

On 25.09.2019 05:11, Chanwoo Choi wrote:
> On 19. 9. 24. 오후 7:11, Leonard Crestez wrote:
>> Register notifiers with the PM QoS framework in order to respond to
>> requests for DEV_PM_QOS_MIN_FREQUENCY and DEV_PM_QOS_MAX_FREQUENCY.
>>
>> No notifiers are added by this patch but PM QoS constraints can be
>> imposed externally (for example from other devices).
>>
>> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
>> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
>> ---
>>   drivers/devfreq/devfreq.c | 75 +++++++++++++++++++++++++++++++++++++++
>>   include/linux/devfreq.h   |  5 +++
>>   2 files changed, 80 insertions(+)
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index eee403e70c84..784f3e40536a 100644
>> --- a/drivers/devfreq/devfreq.c
>> +++ b/drivers/devfreq/devfreq.c
>> @@ -22,15 +22,18 @@
>>   #include <linux/platform_device.h>
>>   #include <linux/list.h>
>>   #include <linux/printk.h>
>>   #include <linux/hrtimer.h>
>>   #include <linux/of.h>
>> +#include <linux/pm_qos.h>
>>   #include "governor.h"
>>   
>>   #define CREATE_TRACE_POINTS
>>   #include <trace/events/devfreq.h>
>>   
>> +#define HZ_PER_KHZ	1000
>> +
>>   static struct class *devfreq_class;
>>   
>>   /*
>>    * devfreq core provides delayed work based load monitoring helper
>>    * functions. Governors can use these or can implement their own
>> @@ -109,10 +112,11 @@ static unsigned long find_available_max_freq(struct devfreq *devfreq)
>>   static void get_freq_range(struct devfreq *devfreq,
>>   			   unsigned long *min_freq,
>>   			   unsigned long *max_freq)
>>   {
>>   	unsigned long *freq_table = devfreq->profile->freq_table;
>> +	unsigned long qos_min_freq, qos_max_freq;
>>   
>>   	lockdep_assert_held(&devfreq->lock);
>>   
>>   	/*
>>   	 * Init min/max frequency from freq table.
>> @@ -125,10 +129,18 @@ static void get_freq_range(struct devfreq *devfreq,
>>   	} else {
>>   		*min_freq = freq_table[devfreq->profile->max_state - 1];
>>   		*max_freq = freq_table[0];
>>   	}
>>   
>> +	/* constraints from PM QoS */
> 
> As I commented on patch4,
> 'constraints' -> 'Constraint' because first verb have to be used
> as the sigular verbs.

Already discussed for another patch; I will modify to "Apply constraints 
from PM QoS" instead.

> I prefer to use following comments:
> 
> 	/* Constraint minimum/maximum frequency from PM QoS constraints */
> 
>> +	qos_min_freq = dev_pm_qos_read_value(devfreq->dev.parent,
>> +					     DEV_PM_QOS_MIN_FREQUENCY);
>> +	qos_max_freq = dev_pm_qos_read_value(devfreq->dev.parent,
>> +					     DEV_PM_QOS_MIN_FREQUENCY);
>> +	*min_freq = max(*min_freq, HZ_PER_KHZ * qos_min_freq);
>> +	*max_freq = min(*max_freq, HZ_PER_KHZ * qos_max_freq);
>> +
>>   	/* constraints from sysfs */
>>   	*min_freq = max(*min_freq, devfreq->min_freq);
>>   	*max_freq = min(*max_freq, devfreq->max_freq);
>>   
>>   	/* constraints from OPP interface */
>> @@ -606,10 +618,49 @@ static int devfreq_notifier_call(struct notifier_block *nb, unsigned long type,
>>   	mutex_unlock(&devfreq->lock);
>>   
>>   	return ret;
>>   }
>>   
>> +/**
>> + * qos_notifier_call() - Common handler for QoS constraints.
>> + * @devfreq:    the devfreq instance.
>> + */
>> +static int qos_notifier_call(struct devfreq *devfreq)
>> +{
>> +	int err;
>> +
>> +	mutex_lock(&devfreq->lock);
>> +	err = update_devfreq(devfreq);
>> +	mutex_unlock(&devfreq->lock);
>> +	if (err)
>> +		dev_err(devfreq->dev.parent,
>> +				"failed to update frequency for PM QoS constraints (%d)\n",
> 
> Is it not over 80 char?

Yes but coding style explicitly forbids breaking strings.

>> +				err);
>> +
>> +	return NOTIFY_OK;
>> +}
>> +
>> +/**
>> + * qos_min_notifier_call() - Callback for QoS min_freq changes.
>> + * @nb:		Should be devfreq->nb_min
>> + */
>> +static int qos_min_notifier_call(struct notifier_block *nb,
>> +					 unsigned long val, void *ptr)
>> +{
>> +	return qos_notifier_call(container_of(nb, struct devfreq, nb_min));
>> +}
>> +
>> +/**
>> + * qos_max_notifier_call() - Callback for QoS max_freq changes.
>> + * @nb:		Should be devfreq->nb_max
>> + */
>> +static int qos_max_notifier_call(struct notifier_block *nb,
>> +					 unsigned long val, void *ptr)
>> +{
>> +	return qos_notifier_call(container_of(nb, struct devfreq, nb_max));
>> +}
>> +
>>   /**
>>    * devfreq_dev_release() - Callback for struct device to release the device.
>>    * @dev:	the devfreq device
>>    *
>>    * Remove devfreq from the list and release its resources.
>> @@ -620,10 +671,15 @@ static void devfreq_dev_release(struct device *dev)
>>   
>>   	mutex_lock(&devfreq_list_lock);
>>   	list_del(&devfreq->node);
>>   	mutex_unlock(&devfreq_list_lock);
>>   
>> +	dev_pm_qos_remove_notifier(devfreq->dev.parent, &devfreq->nb_max,
>> +			DEV_PM_QOS_MAX_FREQUENCY);
>> +	dev_pm_qos_remove_notifier(devfreq->dev.parent, &devfreq->nb_min,
>> +			DEV_PM_QOS_MIN_FREQUENCY);
>> +
> 
> Just print error with dev_err() without stopping the release step.
> 
> I prefer to handle the return value if kernel API provides
> the error code.
> 
>>   	if (devfreq->profile->exit)
>>   		devfreq->profile->exit(devfreq->dev.parent);
>>   
>>   	kfree(devfreq->time_in_state);
>>   	kfree(devfreq->trans_table);
>> @@ -733,10 +789,28 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>   	if (err) {
>>   		put_device(&devfreq->dev);
>>   		goto err_out;
>>   	}
>>   
>> +	/*
>> +	 * Register notifiers for updates to min/max_freq after device is
>> +	 * initialized (and we can handle notifications) but before the
>> +	 * governor is started (which should do an initial enforcement of
>> +	 * constraints).
>> +	 */
> 
> My previous comment is not enough why I prefer to remove it. Sorry.
> Actually, until now, the devfreq_add_device() don't have the detailed
> comments because the line code is not too long. But, at the present time,
> devfreq_add_device() is too long. It means that the detailed comment
> are necessary.
> 
> So, I'll add the detailed comment for each step of devfreq_add_device()
> on separate patch to keep the same style. I'll send the patch to you
> for the review.

This is very likely to result in merge conflicts, maybe wait for my 
series to go in first?

>> +	devfreq->nb_min.notifier_call = qos_min_notifier_call;
>> +	err = dev_pm_qos_add_notifier(devfreq->dev.parent, &devfreq->nb_min,
>> +				      DEV_PM_QOS_MIN_FREQUENCY);
>> +	if (err)
>> +		goto err_devfreq;
>> +
>> +	devfreq->nb_max.notifier_call = qos_max_notifier_call;
>> +	err = dev_pm_qos_add_notifier(devfreq->dev.parent, &devfreq->nb_max,
>> +				      DEV_PM_QOS_MAX_FREQUENCY);
>> +	if (err)
>> +		goto err_devfreq;
>> +
>>   	mutex_lock(&devfreq_list_lock);
>>   
>>   	governor = try_then_request_governor(devfreq->governor_name);
>>   	if (IS_ERR(governor)) {
>>   		dev_err(dev, "%s: Unable to find governor for the device\n",
>> @@ -760,10 +834,11 @@ struct devfreq *devfreq_add_device(struct device *dev,
>>   
>>   	return devfreq;
>>   
>>   err_init:
>>   	mutex_unlock(&devfreq_list_lock);
>> +err_devfreq:
>>   	devfreq_remove_device(devfreq);
>>   	return ERR_PTR(err);
>>   
>>   err_dev:
>>   	/*
>> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
>> index c3cbc15fdf08..dac0dffeabb4 100644
>> --- a/include/linux/devfreq.h
>> +++ b/include/linux/devfreq.h
>> @@ -134,10 +134,12 @@ struct devfreq_dev_profile {
>>    * @total_trans:	Number of devfreq transitions
>>    * @trans_table:	Statistics of devfreq transitions
>>    * @time_in_state:	Statistics of devfreq states
>>    * @last_stat_updated:	The last time stat updated
>>    * @transition_notifier_list: list head of DEVFREQ_TRANSITION_NOTIFIER notifier
>> + * @nb_min:		Notifier block for DEV_PM_QOS_MIN_FREQUENCY
>> + * @nb_max:		Notifier block for DEV_PM_QOS_MAX_FREQUENCY
>>    *
>>    * This structure stores the devfreq information for a give device.
>>    *
>>    * Note that when a governor accesses entries in struct devfreq in its
>>    * functions except for the context of callbacks defined in struct
>> @@ -176,10 +178,13 @@ struct devfreq {
>>   	unsigned int *trans_table;
>>   	unsigned long *time_in_state;
>>   	unsigned long last_stat_updated;
>>   
>>   	struct srcu_notifier_head transition_notifier_list;
>> +
>> +	struct notifier_block nb_min;
>> +	struct notifier_block nb_max;
>>   };
>>   
>>   struct devfreq_freqs {
>>   	unsigned long old;
>>   	unsigned long new;
>>
> 
>