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Subject: Re: [PATCH 1/4] PM / EM: and devices to Energy Model
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Quentin Perret <qperret@google.com>
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References: <20200116152032.11301-1-lukasz.luba@arm.com>
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 <40587d98-0e8d-cbac-dbf5-d26501d47a8c@arm.com>
 <20200120150918.GA164543@google.com>
 <8332c4ac-2a7d-1e2d-76e9-7c979a666257@arm.com>
From:   Lukasz Luba <lukasz.luba@arm.com>
Message-ID: <b02da0ed-9e0b-36db-9813-daa334cbf2ba@arm.com>
Date:   Mon, 20 Jan 2020 18:38:41 +0000
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On 1/20/20 6:27 PM, Dietmar Eggemann wrote:
> On 20/01/2020 16:09, Quentin Perret wrote:
>> Hey Lukasz,
>>
>> On Monday 20 Jan 2020 at 14:52:07 (+0000), Lukasz Luba wrote:
>>> On 1/17/20 10:54 AM, Quentin Perret wrote:
>>>> Suggested alternative: have two registration functions like so:
>>>>
>>>> 	int em_register_dev_pd(struct device *dev, unsigned int nr_states,
>>>> 			       struct em_data_callback *cb);
>>>> 	int em_register_cpu_pd(cpumask_t *span, unsigned int nr_states,
>>>> 			       struct em_data_callback *cb);
>>>
>>> Interesting, in the internal review Dietmar asked me to remove these two
>>> functions. I had the same idea, which would simplify a bit the
>>> registration and it does not need to check the dev->bus if it is CPU.
>>>
>>> Unfortunately, we would need also two function in drivers/opp/of.c:
>>> dev_pm_opp_of_register_cpu_em(policy->cpus);
>>> and
>>> dev_pm_opp_of_register_dev_em(dev);
>>>
>>> Thus, I have created only one registration function, which you can see
>>> in this patch set.
>>
>> Right, I can see how having a unified API would be appealing, but the
>> OPP dependency is a nono, so we'll need to work around one way or
>> another.
>>
>> FWIW, I don't think having separate APIs for CPUs and other devices is
>> that bad given that we already have entirely different frameworks to
>> drive their respective frequencies. And the _cpu variants are basically
>> just wrappers around the _dev ones, so not too bad either IMO :).
> 
> It's true that we need the policy->cpus cpumask only for cpu devices and
> we have it available when we call em_register_perf_domain()
> [scmi-cpufreq.c driver] or the OPP wrapper dev_pm_opp_of_register_em()
> [e.g. cpufreq-dt.c driver].
> 
> And we shouldn't make EM code dependent on OPP.
> 
> But can't we add 'struct cpumask *mask' as an additional argument to
> both which can be set to NULL for (devfreq) devices?
> 
> We can check in em_register_perf_domain() that we got a valid cpumask
> for a cpu device and ignore it for (devfreq) devices.
> 

I think we could avoid this additional argument 'cpumask'. I have
checked the cpufreq_cpu_get function, which should do be good for this:

---------->8-------------------------
static int _get_sharing_cpus(struct device *cpu_dev, struct cpumask *span)
{
         struct cpufreq_policy *policy;

         policy = cpufreq_cpu_get(cpu_dev->id);
         if (policy) {
                 cpumask_copy(span, policy->cpus);
                 cpufreq_cpu_put(policy);
                 return 0;
         } else {
                 return -EINVAL;
         }
}
--------------------------8<-------------------------------

It would be a replacement for:
ret = dev_pm_opp_get_sharing_cpus(dev, span);

Regards,
Lukasz