linux-kernel - Re: [PATCH v1] PM: runtime: Take active children into account in pm_runtime_get_if_in

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Message-ID: <CAPDyKFpGH=ZUyQ0wbkEKVLxknm59hDX6DNm9hXpuqzHCpoe-KQ@mail.gmail.com>
Date: Wed, 9 Jul 2025 13:46:19 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Linux PM <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Sakari Ailus <sakari.ailus@...ux.intel.com>, Alex Elder <elder@...aro.org>, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH v1] PM: runtime: Take active children into account in pm_runtime_get_if_in_use()

On Wed, 9 Jul 2025 at 12:41, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> For all practical purposes, there is no difference between the situation
> in which a given device is not ignoring children and its active child
> count is nonzero and the situation in which its runtime PM usage counter
> is nonzero.  However, pm_runtime_get_if_in_use() will only increment the
> device's usage counter and return 1 in the latter case.
>
> For consistency, make it do so in the former case either by adjusting
> pm_runtime_get_conditional() and update the related kerneldoc comments
> accordingly.
>
> Fixes: c0ef3df8dbae ("PM: runtime: Simplify pm_runtime_get_if_active() usage")
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/base/power/runtime.c |   27 ++++++++++++++++++---------
>  1 file changed, 18 insertions(+), 9 deletions(-)
>
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -1203,10 +1203,12 @@
>   *
>   * Return -EINVAL if runtime PM is disabled for @dev.
>   *
> - * Otherwise, if the runtime PM status of @dev is %RPM_ACTIVE and either
> - * @ign_usage_count is %true or the runtime PM usage counter of @dev is not
> - * zero, increment the usage counter of @dev and return 1. Otherwise, return 0
> - * without changing the usage counter.
> + * Otherwise, if its runtime PM status is %RPM_ACTIVE and (1) @ign_usage_count
> + * is set, or (2) @dev is not ignoring children and its active child count is
> + * nonero, or (3) the runtime PM usage counter of @dev is not zero, increment
> + * the usage counter of @dev and return 1.
> + *
> + * Otherwise, return 0 without changing the usage counter.
>   *
>   * If @ign_usage_count is %true, this function can be used to prevent suspending
>   * the device when its runtime PM status is %RPM_ACTIVE.
> @@ -1228,7 +1230,8 @@
>                 retval = -EINVAL;
>         } else if (dev->power.runtime_status != RPM_ACTIVE) {
>                 retval = 0;
> -       } else if (ign_usage_count) {
> +       } else if (ign_usage_count || (!dev->power.ignore_children &&
> +                  atomic_read(&dev->power.child_count) > 0)) {

I am not sure I understand why this is needed, sorry.

If someone and somehow we have "dev->power.runtime_status ==
RPM_ACTIVE", then the dev's parents/childrens and suppliers/consumers
should have been reference counted correctly already. Otherwise it
should not have been possible to set the runtime_status to RPM_ACTIVE
in the first place, right?

>                 retval = 1;
>                 atomic_inc(&dev->power.usage_count);
>         } else {
> @@ -1261,10 +1264,16 @@
>   * @dev: Target device.
>   *
>   * Increment the runtime PM usage counter of @dev if its runtime PM status is
> - * %RPM_ACTIVE and its runtime PM usage counter is greater than 0, in which case
> - * it returns 1. If the device is in a different state or its usage_count is 0,
> - * 0 is returned. -EINVAL is returned if runtime PM is disabled for the device,
> - * in which case also the usage_count will remain unmodified.
> + * %RPM_ACTIVE and its runtime PM usage counter is greater than 0 or it is not
> + * ignoring children and its active child count is nonzero.  1 is returned in
> + * this case.
> + *
> + * If @dev is in a different state or it is not in use (that is, its usage
> + * counter is 0, or it is ignoring children, or its active child count is 0),
> + * 0 is returned.
> + *
> + * -EINVAL is returned if runtime PM is disabled for the device, in which case
> + * also the usage counter of @dev is not updated.
>   */
>  int pm_runtime_get_if_in_use(struct device *dev)
>  {
>
>
>

Kind regards
Uffe