linux-kernel - Re: [PATCH v3 4/5] PM: hibernate: add new api pm_transition

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Message-ID: <CAJZ5v0j4BuFi_WPPvW64=42Ww=tM8xwpX6gPz8_HX8fJE_Wv1Q@mail.gmail.com>
Date: Tue, 8 Jul 2025 16:39:28 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Mario Limonciello <mario.limonciello@....com>
Cc: Samuel Zhang <guoqing.zhang@....com>, alexander.deucher@....com, 
	christian.koenig@....com, rafael@...nel.org, len.brown@...el.com, 
	pavel@...nel.org, gregkh@...uxfoundation.org, dakr@...nel.org, 
	airlied@...il.com, simona@...ll.ch, ray.huang@....com, matthew.auld@...el.com, 
	matthew.brost@...el.com, maarten.lankhorst@...ux.intel.com, 
	mripard@...nel.org, tzimmermann@...e.de, lijo.lazar@....com, 
	victor.zhao@....com, haijun.chang@....com, Qing.Ma@....com, 
	Owen.Zhang2@....com, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v3 4/5] PM: hibernate: add new api pm_transition_event()

On Tue, Jul 8, 2025 at 4:37 PM Mario Limonciello
<mario.limonciello@....com> wrote:
>
> On 7/8/2025 3:42 AM, Samuel Zhang wrote:
> > dev_pm_ops.thaw() is called in following cases:
> > * normal case: after hibernation image has been created.
> > * error case 1: creation of a hibernation image has failed.
> > * error case 2: restoration from a hibernation image has failed.
> >
> > For normal case, it is called mainly for resume storage devices for
> > saving the hibernation image. Other devices that are not involved
> > in the image saving do not need to resume the device. But since there's
> > no api to know which case thaw() is called, device drivers can't
> > conditionally resume device in thaw().
> >
> > The new pm_transition_event() is such a api to query if thaw() is called
> > in normal case. The returned value in thaw() is:
> > * PM_EVENT_THAW: normal case, no need to resume non-storage devices.
> > * PM_EVENT_RECOVER: error case, need to resume devices.
> >
> > Signed-off-by: Samuel Zhang <guoqing.zhang@....com>
> > ---
> >   drivers/base/power/main.c |  5 +++++
> >   include/linux/pm.h        | 16 ++++++++++++++++
> >   2 files changed, 21 insertions(+)
> >
> > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> > index 40e1d8d8a589..7e0982caa4d4 100644
> > --- a/drivers/base/power/main.c
> > +++ b/drivers/base/power/main.c
> > @@ -62,6 +62,11 @@ static LIST_HEAD(dpm_noirq_list);
> >
> >   static DEFINE_MUTEX(dpm_list_mtx);
> >   static pm_message_t pm_transition;
> > +int pm_transition_event(void)
> > +{
> > +     return pm_transition.event;
> > +}
> > +EXPORT_SYMBOL_GPL(pm_transition_event);
> >
> >   static int async_error;
> >
> > diff --git a/include/linux/pm.h b/include/linux/pm.h
> > index 78855d794342..d1cb77ede1a2 100644
> > --- a/include/linux/pm.h
> > +++ b/include/linux/pm.h
> > @@ -657,6 +657,22 @@ struct pm_subsys_data {
> >   #define DPM_FLAG_SMART_SUSPEND              BIT(2)
> >   #define DPM_FLAG_MAY_SKIP_RESUME    BIT(3)
> >
> > +/**
> > + * pm_transition_event() - Query the current pm transition event value.
> > + *
> > + * Used to query the reason why thaw() is called. It will be one of 2 values:
> > + *
> > + * PM_EVENT_THAW: normal case.
> > + *           hibernation image has been created.
> > + *
> > + * PM_EVENT_RECOVER: error case.
> > + *           creation of a hibernation image or restoration of the main memory
> > + *           contents from a hibernation image has failed.
>
> I don't believe this documentation is complete.  In the use in this
> series those are two events used, but as this is now exported this might
> be used by other callers later which could use it for other PM_EVENT_*.
>
> So because of this I think it's best to convert the comment in
> include/linux/pm.h to kdoc and then reference that from this kdoc.

+1

> > + *
> > + * Return: PM_EVENT_ messages
> > + */
> > +int pm_transition_event(void);
> > +
> >   struct dev_pm_info {
> >       pm_message_t            power_state;
> >       bool                    can_wakeup:1;
>