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

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Message-ID: <7e9488da-d15e-4129-b2d8-ea4de12dd2c8@arm.com>
Date: Thu, 4 Jan 2024 17:27:21 +0000
From: Lukasz Luba <lukasz.luba@....com>
To: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 Viresh Kumar <viresh.kumar@...aro.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 1/4/24 17:11, Dietmar Eggemann wrote:
> 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?

You're referring to the patch 22/23 [1]. Yes, it could be skipped,
but both will go in the same merge window, so not big difference.
I tend to agree that patch 22/23 could belong to this $subject.

As soon as Rafael will merge the core runtime patches, I will
push this small one from this $subject. So it will be in a few
days delay (assuming I would get an Ack from Marek or Krzysztof
for the Exynos patch).

> 
> 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'.
> 
> 
> 

Yes, correct, the rest of API is used (mainly from thermal/dtmp).

[1] 
https://lore.kernel.org/lkml/20240104171553.2080674-23-lukasz.luba@arm.com/