Re: [PATCH v2 2/3] pmdomain: core: add support for power-domains-child-ids

[Kevin Hilman <khilman@baylibre.com>]

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

> On Sat, 11 Apr 2026 at 01:44, Kevin Hilman (TI) <khilman@baylibre.com> wrote:
>>
>> Currently, PM domains can only support hierarchy for simple
>> providers (e.g. ones with #power-domain-cells = 0).
>>
>> Add support for oncell providers as well by adding a new property
>> `power-domains-child-ids` to describe the parent/child relationship.
>>
>> For example, an SCMI PM domain provider has multiple domains, each of
>> which might be a child of diffeent parent domains. In this example,
>> the parent domains are MAIN_PD and WKUP_PD:
>>
>>     scmi_pds: protocol@11 {
>>         reg = <0x11>;
>>         #power-domain-cells = <1>;
>>         power-domains = <&MAIN_PD>, <&WKUP_PD>;
>>         power-domains-child-ids = <15>, <19>;
>>     };
>>
>> With this example using the new property, SCMI PM domain 15 becomes a
>> child domain of MAIN_PD, and SCMI domain 19 becomes a child domain of
>> WKUP_PD.
>>
>> To support this feature, add two new core functions
>>
>> - of_genpd_add_child_ids()
>> - of_genpd_remove_child_ids()
>>
>> which can be called by pmdomain providers to add/remove child domains
>> if they support the new property power-domains-child-ids.
>>
>> The add function is "all or nothing".  If it cannot add all of the
>> child domains in the list, it will unwind any additions already made
>> and report a failure.
>>
>> Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>
>> ---
>>  drivers/pmdomain/core.c   | 166 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  include/linux/pm_domain.h |  16 ++++++++++++++++
>>  2 files changed, 182 insertions(+)
>>
>> diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
>> index 61c2277c9ce3..f978477dd546 100644
>> --- a/drivers/pmdomain/core.c
>> +++ b/drivers/pmdomain/core.c
>> @@ -2909,6 +2909,172 @@ static struct generic_pm_domain *genpd_get_from_provider(
>>         return genpd;
>>  }
>>
>> +/**
>> + * of_genpd_add_child_ids() - Parse power-domains-child-ids property
>> + * @np: Device node pointer associated with the PM domain provider.
>> + * @data: Pointer to the onecell data associated with the PM domain provider.
>> + *
>> + * Parse the power-domains and power-domains-child-ids properties to establish
>> + * parent-child relationships for PM domains. The power-domains property lists
>> + * parent domains, and power-domains-child-ids lists which child domain IDs
>> + * should be associated with each parent.
>> + *
>> + * Uses "all or nothing" semantics: either all relationships are established
>> + * successfully, or none are (any partially-added relationships are unwound
>> + * on error).
>> + *
>> + * Returns 0 on success, -ENOENT if properties don't exist, or negative error code.
>> + */
>
> As I mentioned in my earlier reply for the previous version, returning
> a specific error code when the property doesn't exist will complicate
> handling for the caller. Moreover, we also need to make sure we don't
> returning the same error code (-ENOENT) for a different error further
> down the execution path in of_genpd_add_child_ids(). Otherwise it
> would the caller treat the error code in the wrong way.
>
> To me, there are two better ways to address this. For both options,
> of_genpd_add_child_ids() should return 0 when
> "power-domains-child-ids" is missing.
>
> 1) Add another helper function that checks if
> "power-domains-child-ids" exists. The caller can then use this to
> pre-parse the property and decide whether to treat it as an error.
>
> 2) As I suggested earlier, let of_genpd_add_child_ids() return the
> number of assigned parents/children, while still using the all or
> nothing approach, of course.

OK, I like (2) better.  I'll respin with that approach.

Kevin