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

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

On 19. 9. 26. 오후 10:43, Leonard Crestez wrote:
> On 2019-09-26 4:07 AM, Chanwoo Choi wrote:
>> 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 agree the new comment with 'Apply constraints ... '.
>>
>>>
>>>> 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.
>>
>> How about?
> 
> Modified to dev_warn. This also applies to PATCH 6 so I replied there.
> 
>>>>>    	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?
>>
>> I'll send the separate patch after finished the review of these patches.
>> So, if you agree, please remove this comment on this patch.
>>
>> You can review the detailed comments on separate patch when I send.
> This patch already contains comments and they explain the code being 
> added. Doesn't it make more sense for comments and code to go in together?
> 
> I think the comment is a resonable explanation as to why notifiers are 
> registered at that specific step in the initialization sequence.

If you add this comment on this patch, OK. just I have some comments.

	/*
	 * Register notifiers for updates to min/max_freq after device is
	 * initialized (and we can handle notifications) but before the

I think that 'device is initialized' is not needed.
It is always true, it don't need to add the additional comments.
because dev_pm_qos_add_notifier() must need the 'devfreq->dev'.
The this code prove the call sequence between them.

About 'us', don't use 'we'. The subject is 'devfreq' or other device instead of us.

	 * governor is started (which should do an initial enforcement of
	 * constraints).
 	 */

Actually, it doesn't matter the initialization step between governor
and PM_QOS registration.

If start governor and then register PM_QOS,
the governor can decide the new frequency. And then PM_QOS request
the new constraints for min/max frequency. On request time of PM_QOS,
devfreq can detect this time and then apply the constraints from PM_QOS.

The user of devfreq's PM_QOS must need the phandle or device instance
of devfreq deivce. It means that user of devfreq's PM_QOS can request
the any constraints of PM_QOS_MIN/MAX through PM_QOS interface.

So, it doesn't need to add the following comments
because following comment is not always mandatory.
" governor is started (which should do an initial enforcement of constraints)."

Also, you don't need to use parentheses on comments.

Actually, I think that following comments are enough.

	/* Register PM QoS notifiers for updating to min/max freq */


> 
>>>>> +	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

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