linux-kernel - Re: [PATCH 1/2] OPP: Add API to update EM after adjustment of voltage for OPPs

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Message-ID: <a42ae8dd-383c-43c0-88b4-101303d6f548@arm.com>
Date: Thu, 4 Jan 2024 18:11:56 +0100
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Lukasz Luba <lukasz.luba@....com>, Viresh Kumar <viresh.kumar@...aro.org>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, sboyd@...nel.org, nm@...com,
 linux-samsung-soc@...r.kernel.org, daniel.lezcano@...aro.org,
 rafael@...nel.org, krzysztof.kozlowski@...aro.org, alim.akhtar@...sung.com,
 m.szyprowski@...sung.com, xuewen.yan94@...il.com, mhiramat@...nel.org,
 qyousef@...alina.io, wvw@...gle.com
Subject: Re: [PATCH 1/2] OPP: Add API to update EM after adjustment of voltage
 for OPPs

On 04/01/2024 11:38, Lukasz Luba wrote:
> Hi Viresh,
> 
> On 12/26/23 05:12, Viresh Kumar wrote:
>> On 20-12-23, 11:03, Lukasz Luba wrote:
>>> There are device drivers which can modify voltage values for OPPs. It
>>> could be due to the chip binning and those drivers have specific chip
>>> knowledge about this. This adjustment can happen after Energy Model is
>>> registered, thus EM can have stale data about power.
>>>
>>> Introduce new API function which can be used by device driver which
>>> adjusted the voltage for OPPs. The implementation takes care about
>>> calculating needed internal details in the new EM table ('cost' field).
>>> It plugs in the new EM table to the framework so other subsystems would
>>> use the correct data.
>>>
>>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
>>> ---
>>>   drivers/opp/of.c       | 69 ++++++++++++++++++++++++++++++++++++++++++
>>>   include/linux/pm_opp.h |  6 ++++
>>>   2 files changed, 75 insertions(+)
>>>
>>> diff --git a/drivers/opp/of.c b/drivers/opp/of.c
>>> index 81fa27599d58..992434c0b711 100644
>>> --- a/drivers/opp/of.c
>>> +++ b/drivers/opp/of.c
>>> @@ -1596,3 +1596,72 @@ int dev_pm_opp_of_register_em(struct device
>>> *dev, struct cpumask *cpus)
>>>       return ret;
>>>   }
>>>   EXPORT_SYMBOL_GPL(dev_pm_opp_of_register_em);
>>> +
>>> +/**
>>> + * dev_pm_opp_of_update_em() - Update Energy Model with new power
>>> values
>>> + * @dev        : Device for which an Energy Model has to be registered
>>> + *
>>> + * This uses the "dynamic-power-coefficient" devicetree property to
>>> calculate
>>> + * power values for EM. It uses the new adjusted voltage values
>>> known for OPPs
>>> + * which have changed after boot.
>>> + */
>>> +int dev_pm_opp_of_update_em(struct device *dev)
>>
>> I don't see anything OPP or OF related in this function, I don't think
>> it needs
>> to be part of the OPP core. You just want to reuse _get_power() I
>> guess, which
>> can be exported then.
>>
>> This should really be part of the EM core instead.
>>
> 
> Thank you for having a look at this. OK, that makes sense.
> When I finish the EM runtime modification core features and get them
> merged, I'll continue to work on this patch set. I'll try to follow
> your comment here and export that function (with a different name
> probably).

Just to make sure: If this is the case then you could also add
em_dev_compute_costs() with this new patch instead providing it with the
'Introduce runtime modifiable Energy Model' patch-set?

This would keep dev_pm_opp_of_update_em() and em_dev_compute_costs()
together. IIRC, all the other new EM interfaces you already use with
your 'modifiable EM' use case: '[PATCH v5 14/23] PM: EM: Support late
CPUs booting and capacity adjustment'.