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

[Chanwoo Choi <cw00.choi@samsung.com>]

On 19. 9. 26. 오전 6:18, Leonard Crestez wrote:
> 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.

I want to make it within 80 char. How about following comment?

		dev_err(devfreq->dev.parent,
			"failed to update frequency from PM QoS (%d)\n",

>>> +				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;
>>>
>>
>>
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics