linux-kernel - Re: [PATCH RFC v3 2/2] pmdomain: core: add support for subdomains using power-domain-map

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Message-ID: <7hjz4tnlg6.fsf@baylibre.com>
Date: Mon, 30 Jun 2025 11:17:13 -0700
From: Kevin Hilman <khilman@...libre.com>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 devicetree@...r.kernel.org, linux-pm@...r.kernel.org,
 arm-scmi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v3 2/2] pmdomain: core: add support for subdomains
 using power-domain-map

Ulf Hansson <ulf.hansson@...aro.org> writes:

> [...]
>
>> I've done an implementation with struct device_node *.  This works
>> better (IMO) than struct of_phandle_args * because the caller (in my
>> case scmi_pm_domain.c) already has device nodes, but not phandle args.
>>
>> The result will be that the pmdomain helper will call
>> pm_genpd_add_subdomain() instead of of_genpd_add_subdomain().
>>
>> Below[1] is the current working version, which includes adding the
>> helper to the PM domain core and showing the usage by the SCMI provider.
>>
>> How does this look?
>
> It's a lot better in my opinion. Although, I have a few comments below.
>
>>
>> Note that doing this at provider creation time instead of
>> <genpd>->attach_dev() time will require some changes to
>> of_parse_phandle_with_args_map() because that function expects to be
>> called for a device that has a `power-domains = <provider>` property,
>> not for the provider itself.  But I have it working with some local
>> changes to make that helper work if called for the provider directly.
>> If you're OK with the PM domains approach, I'll post another rev of this
>> series which includes the OF changes for review by DT maintainers.
>>
>> Kevin
>>
>> [1]
>> ---
>>  drivers/pmdomain/arm/scmi_pm_domain.c | 12 ++++++++--
>>  drivers/pmdomain/core.c               | 34 +++++++++++++++++++++++++++
>>  include/linux/pm_domain.h             | 11 ++++++++-
>>  3 files changed, 54 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/pmdomain/arm/scmi_pm_domain.c b/drivers/pmdomain/arm/scmi_pm_domain.c
>> index a7784a8bb5db..8197447e9d17 100644
>> --- a/drivers/pmdomain/arm/scmi_pm_domain.c
>> +++ b/drivers/pmdomain/arm/scmi_pm_domain.c
>> @@ -54,7 +54,7 @@ static int scmi_pd_power_off(struct generic_pm_domain *domain)
>>
>>  static int scmi_pm_domain_probe(struct scmi_device *sdev)
>>  {
>> -       int num_domains, i;
>> +       int num_domains, i, ret;
>>         struct device *dev = &sdev->dev;
>>         struct device_node *np = dev->of_node;
>>         struct scmi_pm_domain *scmi_pd;
>> @@ -115,7 +115,15 @@ static int scmi_pm_domain_probe(struct scmi_device *sdev)
>>
>>         dev_set_drvdata(dev, scmi_pd_data);
>>
>> -       return of_genpd_add_provider_onecell(np, scmi_pd_data);
>> +       ret = of_genpd_add_provider_onecell(np, scmi_pd_data);
>> +       if (ret)
>> +               return ret;
>> +
>> +       /* check for (optional) subdomain mapping with power-domain-map */
>> +       for (i = 0; i < num_domains; i++, scmi_pd++)
>> +               of_genpd_add_subdomain_map(np, domains[i], i);
>> +
>> +       return ret;
>>  }
>>
>>  static void scmi_pm_domain_remove(struct scmi_device *sdev)
>> diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
>> index 88819659df83..3ede4baa4bee 100644
>> --- a/drivers/pmdomain/core.c
>> +++ b/drivers/pmdomain/core.c
>> @@ -3220,6 +3220,40 @@ int of_genpd_parse_idle_states(struct device_node *dn,
>>  }
>>  EXPORT_SYMBOL_GPL(of_genpd_parse_idle_states);
>>
>> +int of_genpd_add_subdomain_map(struct device_node *np,
>> +                              struct generic_pm_domain *domain,
>> +                              int index)
>
> Providing the struct generic_pm_domain *domain as an in-parameter for
> the child-domain seems unnecessary and limiting to me.
>
> Instead I think we should parse the power-domain-map DT property at
> 'index', to find the corresponding child-domain's specifier/index and
> its corresponding parent-domain.
>
> In other words, we don't need the struct generic_pm_domain *domain as
> an in-parameter, right?

I'm not sure I follow.  The `struct generic pm_domain *domain` is the
SCMI child domain.  From the map, we use the index to find the parent
domain.  And then we add the child as a subdomain of the parent.

Are you suggesting that I (re)parse the DT for to find the child domain
also? 

Thanks for the review & guidance,

Kevin