Date:   Mon, 6 Apr 2020 23:17:21 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Lukasz Luba <lukasz.luba@....com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org, linux-omap@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-imx@....com
Cc:     Morten.Rasmussen@....com, Dietmar.Eggemann@....com,
        javi.merino@....com, cw00.choi@...sung.com,
        b.zolnierkie@...sung.com, rjw@...ysocki.net, sudeep.holla@....com,
        viresh.kumar@...aro.org, nm@...com, sboyd@...nel.org,
        rui.zhang@...el.com, amit.kucheria@...durent.com, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, rostedt@...dmis.org,
        qperret@...gle.com, bsegall@...gle.com, mgorman@...e.de,
        shawnguo@...nel.org, s.hauer@...gutronix.de, festevam@...il.com,
        kernel@...gutronix.de, khilman@...nel.org, agross@...nel.org,
        bjorn.andersson@...aro.org, robh@...nel.org,
        matthias.bgg@...il.com, steven.price@....com,
        tomeu.vizoso@...labora.com, alyssa.rosenzweig@...labora.com,
        airlied@...ux.ie, daniel@...ll.ch, liviu.dudau@....com,
        lorenzo.pieralisi@....com, patrick.bellasi@...bug.net,
        orjan.eide@....com, rdunlap@...radead.org, mka@...omium.org
Subject: Re: [PATCH v5 1/5] PM / EM: add devices to Energy Model

On 06/04/2020 18:07, Lukasz Luba wrote:
> 
> 
> On 4/6/20 3:58 PM, Daniel Lezcano wrote:
>>
>> Hi Lukasz,
>>
>>
>> On 06/04/2020 15:29, Lukasz Luba wrote:
>>> Hi Daniel,
>>>
>>> Thank you for the review.
>>>
>>> On 4/3/20 5:05 PM, Daniel Lezcano wrote:
>>>>
>>>> Hi Lukasz,
>>>>
>>>>
>>>> On 18/03/2020 12:45, Lukasz Luba wrote:
>>>>> Add support of other devices into the Energy Model framework not only
>>>>> the
>>>>> CPUs. Change the interface to be more unified which can handle other
>>>>> devices as well.
>>>>
>>>> thanks for taking care of that. Overall I like the changes in this
>>>> patch
>>>> but it hard to review in details because the patch is too big :/
>>>>
>>>> Could you split this patch into smaller ones?
>>>>
>>>> eg. (at your convenience)
>>>>
>>>>    - One patch renaming s/cap/perf/
>>>>
>>>>    - One patch adding a new function:
>>>>
>>>>       em_dev_register_perf_domain(struct device *dev,
>>>>                  unsigned int nr_states,
>>>>                  struct em_data_callback *cb);
>>>>
>>>>      (+ EXPORT_SYMBOL_GPL)
>>>>
>>>>       And em_register_perf_domain() using it.
>>>>
>>>>    - One converting the em_register_perf_domain() user to
>>>>      em_dev_register_perf_domain
>>>>
>>>>    - One adding the different new 'em' functions
>>>>
>>>>    - And finally one removing em_register_perf_domain().
>>>
>>> I agree and will do the split. I could also break the dependencies
>>> for future easier merge.
>>>
>>>>
>>>>
>>>>> Acked-by: Quentin Perret <qperret@...gle.com>
>>>>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
>>>>> ---
>>>>
>>>> [ ... ]
>>>>
>>>>>    2. Core APIs
>>>>> @@ -70,14 +72,16 @@ CONFIG_ENERGY_MODEL must be enabled to use the EM
>>>>> framework.
>>>>>    Drivers are expected to register performance domains into the EM
>>>>> framework by
>>>>>    calling the following API::
>>>>>    -  int em_register_perf_domain(cpumask_t *span, unsigned int
>>>>> nr_states,
>>>>> -                  struct em_data_callback *cb);
>>>>> +  int em_register_perf_domain(struct device *dev, unsigned int
>>>>> nr_states,
>>>>> +        struct em_data_callback *cb, cpumask_t *cpus);
>>>>
>>>> Isn't possible to get rid of this cpumask by using
>>>> cpufreq_cpu_get() which returns the cpufreq's policy and from their get
>>>> the related cpus ?
>>>
>>> We had similar thoughts with Quentin and I've checked this.
>>
>> Yeah, I suspected you already think about that :)
>>
>>> Unfortunately, if the policy is a 'new policy' [1] it gets
>>> allocated and passed into cpufreq driver ->init(policy) [2].
>>> Then that policy is set into per_cpu pointer for each related_cpu [3]:
>>>
>>> for_each_cpu(j, policy->related_cpus)
>>>      per_cpu(cpufreq_cpu_data, j) = policy;
>>>
>>>   Thus, any calls of functions (i.e. cpufreq_cpu_get()) which try to
>>> take this ptr before [3] won't work.
>>>
>>> We are trying to register EM from cpufreq_driver->init(policy) and the
>>> per_cpu policy is likely to be not populated at that phase.
>>
>> What is the problem of registering at the end of the cpufreq_online ?
> 
> We want to enable driver developers to choose one of two options for the
> registration of Energy Model:
> 1. a simple one via dev_pm_opp_of_register_em(), which uses default
>    callback function calculating power based on: voltage, freq
>    and DT entry 'dynamic-power-coefficient' for each OPP
> 2. a more sophisticated, when driver provides callback function, which
>   will be called from EM for each OPP to ask for related power;
>   This interface could also be used by devices which relay not only
>   on one source of 'voltage', i.e. manipulate body bias or have
>   other controlling voltage for gates in the new 3D transistors. They
>   might provide custom callback function in their cpufreq driver.
>   This is used i.e. in cpufreq drivers which use firmware to get power,
>   like scmi-cpufreq.c;
> 
> To meet this requirement the registration of EM is moved into cpufreq
> drivers, not in the framework i.e cpufreq_online(). If we could limit
> the support for only option 1. then we could move the registration
> call into cpufreq framework and clean the cpufreq drivers.

I'm not sure to get your point but I think a series setting the scene by
moving the dev_pm_opp_of_register_em() to cpufreq_online() and remove
the cpumask may make sense.

Can you send the split version of patch 1/5 as a series without the
other changes ? So we can focus on first ?


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