linux-kernel - Re: [RESEND][PATCH v2 3/4] PM: EM: Add em_dev_update_chip

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Date: Wed, 27 Mar 2024 13:55:34 +0100
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Lukasz Luba <lukasz.luba@....com>
Cc: linux-arm-kernel@...ts.infradead.org, sboyd@...nel.org, nm@...com,
 linux-samsung-soc@...r.kernel.org, daniel.lezcano@...aro.org,
 rafael@...nel.org, viresh.kumar@...aro.org, krzysztof.kozlowski@...aro.org,
 alim.akhtar@...sung.com, m.szyprowski@...sung.com, mhiramat@...nel.org,
 linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [RESEND][PATCH v2 3/4] PM: EM: Add em_dev_update_chip_binning()

On 26/03/2024 21:32, Lukasz Luba wrote:
> 
> 
> On 3/26/24 10:09, Dietmar Eggemann wrote:
>> On 22/03/2024 12:08, Lukasz Luba wrote:

[...]

>>> +    return em_recalc_and_update(dev, pd, em_table);
>>> +}
>>> +EXPORT_SYMBOL_GPL(em_dev_update_chip_binning);
>>
>> In the previous version of 'chip-binning' you were using the new EM
>> interface em_dev_compute_costs() (1) which is now replaced by
>> em_recalc_and_update() -> em_compute_costs().
>>
>> https://lkml.kernel.org/r/20231220110339.1065505-2-lukasz.luba@arm.com
>>
>> Which leaves (1) still unused.
>>
>> That was why my concern back then that we shouldn't introduce EM
>> interfaces without a user:
>>
>> https://lkml.kernel.org/r/8fc499cf-fca1-4465-bff7-a93dfd36f3c8@arm.com
>>
>> What happens now with em_dev_compute_costs()?
>>
> 
> For now it's not used, but modules which will create new EMs
> with custom power values will use it. When such a module have
> e.g. 5 EMs for one PD and only switches on one of them, then
> this em_dev_compute_costs() will be used at setup for those
> 5 EMs. Later it won't be used.
> I don't wanted to combine the registration of new EM with
> the compute cost, because that will create overhead in the
> switching to new EM code path. Now we have only ~3us, which
> was the main goal.
> 
> When our scmi-cpufreq get the support for EM update this
> compute cost will be used there.

OK, I see. I checked the reloadable EM test module and
em_dev_compute_costs() is used there like you described it.