linux-kernel - Re: [PATCH v2] PM: sleep: core: Fix runtime PM enabling in device_resume

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Message-ID: <CAPDyKFqzt70rkHaRP62zErkMi2kFC1iY-NHPWjK0FWZSjZ00jA@mail.gmail.com>
Date: Tue, 18 Nov 2025 13:17:19 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: linux-pm@...r.kernel.org, Rose Wu <ya-jou.wu@...iatek.com>, 
	rafael.j.wysocki@...el.com, regressions@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, wsd_upstream <wsd_upstream@...iatek.com>, 
	linux-mediatek@...ts.infradead.org, "artis. chiu" <artis.chiu@...iatek.com>, 
	"Johnny-cc. Kao" <Johnny-cc.Kao@...iatek.com>
Subject: Re: [PATCH v2] PM: sleep: core: Fix runtime PM enabling in device_resume_early()

On Tue, 18 Nov 2025 at 12:48, Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Tuesday, November 18, 2025 9:31:08 AM CET Rose Wu wrote:
> > Hi,
> >
> > On Mon, 2025-11-17 at 19:57 +0100, Rafael J. Wysocki wrote:
> > >
> > > Make two changes to address this problem.
> > >
> > > First, reorder device_suspend_late() to only disable runtime PM for a
> > > device if the power.is_late_suspended flag is going to be set for it.
> > > In all of the other cases, disabling runtime PM for the device is not
> > > in fact necessary.
> > >
> > > Second, make device_resume_early() only enable runtime PM for the
> > > devices with the power.is_late_suspended flag set.
> > >
> >
> > My concern is with the error path in device_suspend_late().
> > If a device fails its dpm_run_callback(), it appears that its
> > power.is_late_suspended flag is not set, potentially leaving its runtime
> > PM disabled during the resume sequence.
>
> Right, pm_runtime_enable() is missing in the error path after calling
> dpm_run_callback().
>
> ---
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> Runtime PM should only be enabled in device_resume_early() if it has
> been disabled for the given device by device_suspend_late().  Otherwise,
> it may cause runtime PM callbacks to run prematurely in some cases
> which leads to further functional issues.
>
> Make two changes to address this problem.
>
> First, reorder device_suspend_late() to only disable runtime PM for a
> device when it is going to look for the device's callback.  In all of
> the other cases, disabling runtime PM for the device is not in fact
> necessary.  However, if the device's callback returns an error and the
> power.is_late_suspended flag is not going to be set, enable runtime
> PM so it only remains disabled when power.is_late_suspended is set.
>
> Second, make device_resume_early() only enable runtime PM for the
> devices with the power.is_late_suspended flag set.
>
> Fixes: 443046d1ad66 ("PM: sleep: Make suspend of devices more asynchronous")
> Reported-by: Rose Wu <ya-jou.wu@...iatek.com>
> Closes: https://lore.kernel.org/linux-pm/70b25dca6f8c2756d78f076f4a7dee7edaaffc33.camel@mediatek.com/
> Cc: 6.16+ <stable@...r.kernel.org> # 6.16+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>
> v1 -> v2: Add pm_runtime_enable() to device_suspend_late() error path (Rose).
>
> ---
>  drivers/base/power/main.c |   15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
>
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -941,11 +941,11 @@ Run:
>
>  Skip:
>         dev->power.is_late_suspended = false;
> +       pm_runtime_enable(dev);
>
>  Out:
>         TRACE_RESUME(error);
>
> -       pm_runtime_enable(dev);
>         complete_all(&dev->power.completion);
>
>         if (error) {
> @@ -1630,12 +1630,6 @@ static void device_suspend_late(struct d
>         TRACE_DEVICE(dev);
>         TRACE_SUSPEND(0);
>
> -       /*
> -        * Disable runtime PM for the device without checking if there is a
> -        * pending resume request for it.
> -        */
> -       __pm_runtime_disable(dev, false);
> -
>         dpm_wait_for_subordinate(dev, async);
>
>         if (READ_ONCE(async_error))
> @@ -1649,6 +1643,12 @@ static void device_suspend_late(struct d
>         if (dev->power.syscore || dev->power.direct_complete)
>                 goto Complete;
>
> +       /*
> +        * Disable runtime PM for the device without checking if there is a
> +        * pending resume request for it.
> +        */
> +       __pm_runtime_disable(dev, false);
> +

Moving this here means we are going to keep runtime pm enabled for
syscore devices during system wide suspend/resume. That's quite a
change in behaviour for a fix for a regression, I think. Not saying
that it can't work though.

Although, perhaps better to call __pm_runtime_disable() a few lines
earlier and use a separate flag to track that we need to call
pm_runtime_enable() in device_resume_early()?

>         if (dev->pm_domain) {
>                 info = "late power domain ";
>                 callback = pm_late_early_op(&dev->pm_domain->ops, state);
> @@ -1679,6 +1679,7 @@ Run:
>                 WRITE_ONCE(async_error, error);
>                 dpm_save_failed_dev(dev_name(dev));
>                 pm_dev_err(dev, state, async ? " async late" : " late", error);
> +               pm_runtime_enable(dev);
>                 goto Complete;
>         }
>         dpm_propagate_wakeup_to_parent(dev);
>
>
>

Kind regards
Uffe