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

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Message-ID: <CAPDyKFq2-D2vDSK0Z=qjX9vACrtvcYaAWmT=w2iVqwUfhzWD2w@mail.gmail.com>
Date: Mon, 2 Jun 2025 12:04:09 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Kevin Hilman <khilman@...libre.com>
Cc: Rob Herring <robh@...nel.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

On Wed, 28 May 2025 at 23:59, Kevin Hilman <khilman@...libre.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 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>
> ---
>  drivers/pmdomain/core.c | 166 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 166 insertions(+)
>
> diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
> index d6c1ddb807b2..b8e505516f3d 100644
> --- a/drivers/pmdomain/core.c
> +++ b/drivers/pmdomain/core.c
> @@ -2441,6 +2441,9 @@ static LIST_HEAD(of_genpd_providers);
>  /* Mutex to protect the list above. */
>  static DEFINE_MUTEX(of_genpd_mutex);
>
> +static int of_genpd_parse_domains_map(struct device_node *np,
> +                                     struct genpd_onecell_data *data);
> +
>  /**
>   * genpd_xlate_simple() - Xlate function for direct node-domain mapping
>   * @genpdspec: OF phandle args to map into a PM domain
> @@ -2635,6 +2638,14 @@ int of_genpd_add_provider_onecell(struct device_node *np,
>         if (ret < 0)
>                 goto error;
>
> +       /* Parse power-domains-map property for Nexus node mapping */
> +       ret = of_genpd_parse_domains_map(np, data);
> +       if (ret < 0 && ret != -ENOENT) {
> +               pr_err("Failed to parse power-domains-map for %pOF: %d\n", np, ret);
> +               of_genpd_del_provider(np);
> +               goto error;
> +       }

To be consistent with the current way for how we usually add
parent/child-domains in genpd (see of_genpd_add|remove_subdomain), I
suggest we keep this part being specific to each genpd provider
driver, rather than calling this from of_genpd_add_provider_onecell().

That said, I don't mind if we need to export another genpd helper
function along the lines of of_genpd_parse_domains_map() as below.
Also don't forget to consider if there is a corresponding "cleanup"
helper function needed.

[...]

Kind regards
Uffe