linux-kernel - Re: [PATCH RFC v2 2/2] pmdomain: core: use DT map to support hierarchy

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Message-ID: <7h1prnqn3v.fsf@baylibre.com>
Date: Fri, 13 Jun 2025 15:43:16 -0700
From: Kevin Hilman <khilman@...libre.com>
To: Rob Herring <robh@...nel.org>
Cc: Ulf Hansson <ulf.hansson@...aro.org>, Krzysztof Kozlowski
 <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, "Rafael J.
 Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 arm-scmi@...r.kernel.org
Subject: Re: [PATCH RFC v2 2/2] pmdomain: core: use DT map to support hierarchy

Kevin Hilman <khilman@...libre.com> writes:

> Hi Rob,
>
> Rob Herring <robh@...nel.org> writes:
>
>> On Wed, May 28, 2025 at 02:58:52PM -0700, Kevin Hilman 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 support for a nexus
>>> node map, as described in section 2.5.1 of the DT spec.
>>> 
>>> For example, an SCMI PM domain provider might be a subdomain of
>>> multiple 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-domain-map = <15 &MAIN_PD>,
>>>                            <19 &WKUP_PD>;
>>>     };
>>> 
>>> With the new map, child domain 15 (scmi_pds 15) becomes a
>>> subdomain of MAIN_PD, and child domain 19 (scmi_pds 19) becomes a
>>> subdomain of WKUP_PD.
>>> 
>>> Signed-off-by: Kevin Hilman <khilman@...libre.com>
>
> [...]
>
>>> +/**
>>> + * of_genpd_parse_domains_map() - Parse power-domains-map property for Nexus mapping
>>> + * @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-map property to establish parent-child relationships
>>> + * for PM domains using Nexus node mapping as defined in the device tree
>>> + * specification section v2.5.1.
>>> + *
>>> + * The power-domains-map property format is:
>>> + * power-domains-map = <child_specifier target_phandle [target_specifier]>, ...;
>>> + *
>>> + * Where:
>>> + * - child_specifier: The child domain ID that should be mapped
>>> + * - target_phandle: Phandle to the parent PM domain provider
>>> + * - target_specifier: Optional arguments for the parent provider (if it has #power-domain-cells > 0)
>>> + *
>>> + * Returns 0 on success, -ENOENT if property doesn't exist, or negative error code.
>>> + */
>>> +static int of_genpd_parse_domains_map(struct device_node *np,
>>> +				      struct genpd_onecell_data *data)
>>> +{
>>> +	struct of_phandle_args parent_args;
>>> +	struct generic_pm_domain *parent_genpd, *child_genpd;
>>> +	u32 *map_entries;
>>> +	int map_len, child_cells, i, ret;
>>> +	u32 child_id;
>>> +
>>> +	/* Check if power-domains-map property exists */
>>> +	map_len = of_property_count_u32_elems(np, "power-domains-map");
>>> +	if (map_len <= 0)
>>> +		return -ENOENT;
>>
>> Don't implement your own map parsing. Use or extend 
>> of_parse_phandle_with_args_map().
>
> So I've been wrestling with this for a bit, and I need some guidance.
> TBH, these "nexus node maps" and of_parse_phandle_with_args_map() are
> breaking my brain.

OK, nevermind.  I *think* I have a better grasp on how they should be used
now.  I've submitted a v3 of the RFC[1], but could defintely still use
some guidance.

Kevin

[1] https://lore.kernel.org/linux-pm/20250613-pmdomain-hierarchy-onecell-v3-0-5c770676fce7@baylibre.com/