Re: [PATCH 3/5] thermal: devfreq_cooling: add new registration functions with Energy Model

[Lukasz Luba <lukasz.luba@arm.com>]

On 10/7/20 1:07 PM, Ionela Voinescu wrote:
> Hi Lukasz,
> 
> On Monday 21 Sep 2020 at 13:20:05 (+0100), Lukasz Luba wrote:
>> The Energy Model (EM) framework supports devices such as Devfreq. Create
>> new registration functions which automatically register EM for the thermal
>> devfreq_cooling devices. This patch prepares the code for coming changes
>> which are going to replace old power model with the new EM.
>>
>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
>> ---
>>   drivers/thermal/devfreq_cooling.c | 99 ++++++++++++++++++++++++++++++-
>>   include/linux/devfreq_cooling.h   | 22 +++++++
>>   2 files changed, 120 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/thermal/devfreq_cooling.c b/drivers/thermal/devfreq_cooling.c
>> index cf045bd4d16b..7e091e795284 100644
>> --- a/drivers/thermal/devfreq_cooling.c
>> +++ b/drivers/thermal/devfreq_cooling.c
>> @@ -50,6 +50,8 @@ static DEFINE_IDA(devfreq_ida);
>>    * @capped_state:	index to cooling state with in dynamic power budget
>>    * @req_max_freq:	PM QoS request for limiting the maximum frequency
>>    *			of the devfreq device.
>> + * @em:		Energy Model which represents the associated Devfreq device
>                                       ^^^^^^^^^^^^^^^^
> 				     for

I will change it.

>> + * @em_registered:	Devfreq cooling registered the EM and should free it.
>>    */
>>   struct devfreq_cooling_device {
>>   	int id;
>> @@ -63,6 +65,8 @@ struct devfreq_cooling_device {
>>   	u32 res_util;
>>   	int capped_state;
>>   	struct dev_pm_qos_request req_max_freq;
>> +	struct em_perf_domain *em;
>> +	bool em_registered;
>>   };
>>   
>>   static int devfreq_cooling_get_max_state(struct thermal_cooling_device *cdev,
>> @@ -586,22 +590,115 @@ struct thermal_cooling_device *devfreq_cooling_register(struct devfreq *df)
>>   }
>>   EXPORT_SYMBOL_GPL(devfreq_cooling_register);
>>   
>> +/**
>> + * devfreq_cooling_em_register_power() - Register devfreq cooling device with
>> + *		power information and attempt to register Energy Model (EM)
> 
> It took me a while to understand the differences between devfreq
> register functions and it left me with a nagging feeling that we don't
> need all of them. Also, looking over the cpufreq cooling devices, they
> keep their registering interfaces quite simple.

This was discussed in previous series, related to EM core changes.
It was requested to have a helper registration function which would
create EM automatically.

> 
> With the functions added by this patch, the devfreq cooling devices will have:
>   - old:
>         of_devfreq_cooling_register_power
>         of_devfreq_cooling_register
>         devfreq_cooling_register
>         devfreq_cooling_unregister
>   - new:
>         devfreq_cooling_em_register_power
>         devfreq_cooling_em_register
> 
> My question is whether we actually need the two new
> devfreq_cooling_em_register_power() and devfreq_cooling_em_register()?

It is just for consistency, with older scheme. It is only a wrapper, one
line, with default NULL. This scheme is common in thermal and some other
frameworks.

> 
> The power_ops and the em are dependent on one another, so could we
> extend the of_devfreq_cooling_register_power() to do the additional em
> registration. We only need a way to pass the em_cb and I think that
> could fit nicely in devfreq_cooling_power.

No, they aren't 'dependent on one another'. The EM usage doesn't depend
on presence of power_ops. Drivers might not support power_ops, but want
the framework still use EM and do power estimation.

> 
> To be noted that I've reviewed these interfaces in the context of the
> final state of devfreq_cooling.c, after the changes in 4/5.
> 
>> + * @df:		Pointer to devfreq device.
>> + * @dfc_power:	Pointer to devfreq_cooling_power.
>> + * @em_cb:	Callback functions providing the data of the EM
>> + *
>> + * Register a devfreq cooling device and attempt to register Energy Model. The
>> + * available OPPs must be registered for the device.
>> + *
>> + * If @dfc_power is provided, the cooling device is registered with the
>> + * power extensions. If @em_cb is provided it will be called for each OPP to
>> + * calculate power value and cost. If @em_cb is not provided then simple Energy
>> + * Model is going to be used, which requires "dynamic-power-coefficient" a
>> + * devicetree property.
>> + */
>> +struct thermal_cooling_device *
>> +devfreq_cooling_em_register_power(struct devfreq *df,
>> +				  struct devfreq_cooling_power *dfc_power,
>> +				  struct em_data_callback *em_cb)
>> +{
>> +	struct thermal_cooling_device *cdev;
>> +	struct devfreq_cooling_device *dfc;
>> +	struct device_node *np = NULL;
>> +	struct device *dev;
>> +	int nr_opp, ret;
>> +
>> +	if (IS_ERR_OR_NULL(df))
>> +		return ERR_PTR(-EINVAL);
>> +
>> +	dev = df->dev.parent;
>> +
>> +	if (em_cb) {
>> +		nr_opp = dev_pm_opp_get_opp_count(dev);
>> +		if (nr_opp <= 0) {
>> +			dev_err(dev, "No valid OPPs found\n");
>> +			return ERR_PTR(-EINVAL);
>> +		}
>> +
>> +		ret = em_dev_register_perf_domain(dev, nr_opp, em_cb, NULL);
>> +	} else {
>> +		ret = dev_pm_opp_of_register_em(dev, NULL);
>> +	}
>> +
>> +	if (ret)
>> +		dev_warn(dev, "Unable to register EM for devfreq cooling device (%d)\n",
>> +			 ret);
>> +
>> +	if (dev->of_node)
>> +		np = of_node_get(dev->of_node);
>> +
>> +	cdev = of_devfreq_cooling_register_power(np, df, dfc_power);
>> +
>> +	if (np)
>> +		of_node_put(np);
>> +
>> +	if (IS_ERR_OR_NULL(cdev)) {
>> +		if (!ret)
>> +			em_dev_unregister_perf_domain(dev);
>> +	} else {
>> +		dfc = cdev->devdata;
>> +		dfc->em_registered = !ret;
>> +	}
>> +
>> +	return cdev;
>> +}
>> +EXPORT_SYMBOL_GPL(devfreq_cooling_em_register_power);
>> +
>> +/**
>> + * devfreq_cooling_em_register() - Register devfreq cooling device together
>> + *				with Energy Model.
>> + * @df:		Pointer to devfreq device.
>> + * @em_cb:	Callback functions providing the data of the Energy Model
>> + *
>> + * This function attempts to register Energy Model for devfreq device and then
>> + * register the devfreq cooling device.
>> + */
>> +struct thermal_cooling_device *
>> +devfreq_cooling_em_register(struct devfreq *df, struct em_data_callback *em_cb)
>> +{
>> +	return devfreq_cooling_em_register_power(df, NULL, em_cb);
>> +}
>> +EXPORT_SYMBOL_GPL(devfreq_cooling_em_register);
>> +
>>   /**
>>    * devfreq_cooling_unregister() - Unregister devfreq cooling device.
>>    * @cdev: Pointer to devfreq cooling device to unregister.
>> + *
>> + * Unregisters devfreq cooling device and related Energy Model if it was
>> + * present.
>>    */
>>   void devfreq_cooling_unregister(struct thermal_cooling_device *cdev)
>>   {
>>   	struct devfreq_cooling_device *dfc;
>> +	struct device *dev;
>>   
>> -	if (!cdev)
>> +	if (IS_ERR_OR_NULL(cdev))
>>   		return;
>>   
>>   	dfc = cdev->devdata;
>> +	dev = dfc->devfreq->dev.parent;
>>   
>>   	thermal_cooling_device_unregister(dfc->cdev);
>>   	ida_simple_remove(&devfreq_ida, dfc->id);
>>   	dev_pm_qos_remove_request(&dfc->req_max_freq);
>> +
>> +	if (dfc->em_registered)
>> +		em_dev_unregister_perf_domain(dev);
> 
> Nit: Isn't it enough to check if dev->em_pd != NULL to be able to
> unregister the perf_domain? That would remove the need for
> dfc->em_registered.

The devfreq cooling may only unregister the EM if it has registered it.
If any other code did the registration, it should unregister when it
finished using it.

> 
> I suppose one could say that's using implementation details on how the
> EM is built and stored and we should not rely on it, so it's up to you
> if you want to change it.
> 
> Kind regards,
> Ionela.
> 
>> +
>>   	kfree(dfc->power_table);
>>   	kfree(dfc->freq_table);
>>   
>> diff --git a/include/linux/devfreq_cooling.h b/include/linux/devfreq_cooling.h
>> index 9df2dfca68dd..19868fb922f1 100644
>> --- a/include/linux/devfreq_cooling.h
>> +++ b/include/linux/devfreq_cooling.h
>> @@ -11,6 +11,7 @@
>>   #define __DEVFREQ_COOLING_H__
>>   
>>   #include <linux/devfreq.h>
>> +#include <linux/energy_model.h>
>>   #include <linux/thermal.h>
>>   
>>   
>> @@ -65,6 +66,13 @@ struct thermal_cooling_device *
>>   of_devfreq_cooling_register(struct device_node *np, struct devfreq *df);
>>   struct thermal_cooling_device *devfreq_cooling_register(struct devfreq *df);
>>   void devfreq_cooling_unregister(struct thermal_cooling_device *dfc);
>> +struct thermal_cooling_device *
>> +devfreq_cooling_em_register_power(struct devfreq *df,
>> +				  struct devfreq_cooling_power *dfc_power,
>> +				  struct em_data_callback *em_cb);
>> +struct thermal_cooling_device *
>> +devfreq_cooling_em_register(struct devfreq *df,
>> +			    struct em_data_callback *em_cb);
>>   
>>   #else /* !CONFIG_DEVFREQ_THERMAL */
>>   
>> @@ -87,6 +95,20 @@ devfreq_cooling_register(struct devfreq *df)
>>   	return ERR_PTR(-EINVAL);
>>   }
>>   
>> +static inline struct thermal_cooling_device *
>> +devfreq_cooling_em_register_power(struct devfreq *df,
>> +				  struct devfreq_cooling_power *dfc_power,
>> +				  struct em_data_callback *em_cb)
>> +{
>> +	return ERR_PTR(-EINVAL);
>> +}
>> +
>> +static inline struct thermal_cooling_device *
>> +devfreq_cooling_em_register(struct devfreq *df,	struct em_data_callback *em_cb)
>> +{
>> +	return ERR_PTR(-EINVAL);
>> +}
>> +
>>   static inline void
>>   devfreq_cooling_unregister(struct thermal_cooling_device *dfc)
>>   {
>> -- 
>> 2.17.1
>>
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