Re: [PATCH v2 2/3] pmdomain: core: add genpd_for_each_child() helper

[Ulf Hansson]

On Fri, 6 Feb 2026 at 01:30, Kevin Hilman (TI) <khilman@xxxxxxxxxxxx> wrote:
>
> Add a new internal helper function genpd_for_each_child() that recursively
> iterates over all devices in a PM domain and its child domains (subdomains).
> This helper is useful for governors and other core PM domain code that needs
> to examine or apply operations to all devices within a domain hierarchy.
>
> The function takes a callback that is invoked for each device, and supports
> early termination if the callback returns a non-zero value.
>
> The helper is defined in a new internal header drivers/pmdomain/core.h and
> implemented in drivers/pmdomain/core.c, making it available to other PM
> domain subsystem components.

I think it's important to state that this isn't for pmdomain providers
to use, but only for the core and the governor. Perhaps add a comment
about that too in the function description.

That said, if there is only one user, perhaps adding a helper isn't
worth it after all?

>
> The first user of this helper is the cpu_system_power_down_ok() governor
> function, which uses it to check device QoS latency constraints across the
> entire domain hierarchy.
>
> Signed-off-by: Kevin Hilman (TI) <khilman@xxxxxxxxxxxx>
> ---
>  drivers/pmdomain/core.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>  drivers/pmdomain/core.h | 17 +++++++++++++++++
>  2 files changed, 59 insertions(+)
>
> diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
> index bf82775f6a67..41c987fc5c5a 100644
> --- a/drivers/pmdomain/core.c
> +++ b/drivers/pmdomain/core.c
> @@ -24,6 +24,8 @@
>  #include <linux/cpu.h>
>  #include <linux/debugfs.h>
>
> +#include "core.h"
> +
>  /* Provides a unique ID for each genpd device */
>  static DEFINE_IDA(genpd_ida);
>
> @@ -281,6 +283,46 @@ static void genpd_sd_counter_inc(struct generic_pm_domain *genpd)
>         smp_mb__after_atomic();
>  }
>
> +/**
> + * genpd_for_each_child - Recursively iterate over all devices
> + *                        in a PM domain and its subdomains.
> + * @genpd: PM domain to iterate over.
> + * @fn: Callback function to invoke for each device.
> + * @data: Data to pass to the callback function.
> + *
> + * This function recursively walks through all devices in the given PM domain
> + * and all devices in its child PM domains (subdomains). For each device found,
> + * the callback function @fn is invoked with the device and @data as arguments.
> + *
> + * Returns: 0 on success, or the first non-zero value returned by @fn.
> + */
> +int genpd_for_each_child(struct generic_pm_domain *genpd,
> +                        int (*fn)(struct device *dev, void *data),
> +                        void *data)
> +{
> +       struct pm_domain_data *pdd;
> +       struct gpd_link *link;
> +       int ret;
> +
> +       /* First, iterate over all devices in this domain */
> +       list_for_each_entry(pdd, &genpd->dev_list, list_node) {
> +               ret = fn(pdd->dev, data);
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       /* Then, recursively iterate over all child domains (subdomains) */
> +       list_for_each_entry(link, &genpd->parent_links, parent_node) {
> +               struct generic_pm_domain *child_pd = link->child;
> +
> +               ret = genpd_for_each_child(child_pd, fn, data);
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       return 0;
> +}
> +
>  #ifdef CONFIG_DEBUG_FS
>  static struct dentry *genpd_debugfs_dir;
>
> diff --git a/drivers/pmdomain/core.h b/drivers/pmdomain/core.h
> new file mode 100644
> index 000000000000..7061891d31fb
> --- /dev/null
> +++ b/drivers/pmdomain/core.h
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Internal header for PM domain core
> + *
> + * Copyright (C) 2011 Rafael J. Wysocki <rjw@xxxxxxx>, Renesas Electronics Corp.
> + */
> +
> +#ifndef __PM_DOMAIN_CORE_H__
> +#define __PM_DOMAIN_CORE_H__
> +
> +#include <linux/pm_domain.h>
> +
> +int genpd_for_each_child(struct generic_pm_domain *genpd,
> +                        int (*fn)(struct device *dev, void *data),
> +                        void *data);
> +
> +#endif /* __PM_DOMAIN_CORE_H__ */
>
> --
> 2.51.0
>

Kind regards
Uffe