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

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Message-ID: <CAJZ5v0jEELFB6vb1dtkPgu_3_eew7Y1Jebevfmhye+ZPLk0Jtg@mail.gmail.com>
Date: Tue, 15 Jul 2025 14:46:21 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>, Linux PM <linux-pm@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, Alex Elder <elder@...aro.org>, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>, Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v1] PM: runtime: Take active children into account in pm_runtime_get_if_in_use()

Hi Sakari,

On Tue, Jul 15, 2025 at 9:28 AM Sakari Ailus
<sakari.ailus@...ux.intel.com> wrote:
>
> Hi Rafael,
>
> Thanks for the patch.
>
> On Wed, Jul 09, 2025 at 12:41:45PM +0200, Rafael J. Wysocki 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")
>
> I guess this should be:
>
> Fixes: c111566bea7c ("PM: runtime: Add pm_runtime_get_if_active()")

Technically yes, but that would require specific backport changes for
older "stable" series.

> Should this also be cc'd to stable?

Possibly.

> Reviewed-by: Sakari Ailus <sakari.ailus@...ux.intel.com>

Thank you!

> > 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)) {
> >               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,
>
> Sakari Ailus
>