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

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

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.

>>>> +	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;
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