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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Fri, 27 Aug 2021 14:21:00 +0200
Message-ID: <CAJZ5v0jBBx93WVz4DohwiBTEXhJtpA1=+_vyqE2=iBzm6MrbGw@mail.gmail.com>
Subject: Re: [PATCH v4] PM: sleep: core: Avoid setting power.must_resume to false
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     Prasad Sodagudi <psodagud@codeaurora.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Len Brown <len.brown@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Pavel Machek <pavel@ucw.cz>
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On Fri, Aug 27, 2021 at 10:58 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Mon, Aug 23, 2021 at 08:27:50AM -0700, Prasad Sodagudi wrote:
> > There are variables(power.may_skip_resume and dev->power.must_resume)
> > and DPM_FLAG_MAY_SKIP_RESUME flags to control the resume of devices after
> > a system wide suspend transition.
> >
> > Setting the DPM_FLAG_MAY_SKIP_RESUME flag means that the driver allows
> > its "noirq" and "early" resume callbacks to be skipped if the device
> > can be left in suspend after a system-wide transition into the working
> > state. PM core determines that the driver's "noirq" and "early" resume
> > callbacks should be skipped or not with dev_pm_skip_resume() function by
> > checking power.may_skip_resume variable.
> >
> > power.must_resume variable is getting set to false in __device_suspend()
> > function without checking device's DPM_FLAG_MAY_SKIP_RESUME settings.
> > In problematic scenario, where all the devices in the suspend_late
> > stage are successful and some device can fail to suspend in
> > suspend_noirq phase. So some devices successfully suspended in suspend_late
> > stage are not getting chance to execute __device_suspend_noirq()
> > to set dev->power.must_resume variable to true and not getting
> > resumed in early_resume phase.
> >
> > Add a check for device's DPM_FLAG_MAY_SKIP_RESUME flag before
> > setting power.must_resume variable in __device_suspend function.
> >
> > Fixes: 6e176bf8d461 ("PM: sleep: core: Do not skip callbacks in the resume phase")
> > Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>
> > ---
> >  V3 -> V4: Remove dev->power.usage_count variable check
> >  V2 -> V3: Format issues patch posting
> >  V1 -> V2: Fixed indentation and commit text to include scenario
> >  drivers/base/power/main.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> > index d568772..50e8ea3 100644
> > --- a/drivers/base/power/main.c
> > +++ b/drivers/base/power/main.c
> > @@ -1642,7 +1642,10 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
> >       }
> >
> >       dev->power.may_skip_resume = true;
> > -     dev->power.must_resume = false;
> > +     if (dev_pm_test_driver_flags(dev, DPM_FLAG_MAY_SKIP_RESUME))
> > +             dev->power.must_resume = false;
> > +     else
> > +             dev->power.must_resume = true;
> >
> >       dpm_watchdog_set(&wd, dev);
> >       device_lock(dev);
>
> Seems sane, Rafael, any comments?

Yup, please see my response:
https://lore.kernel.org/linux-pm/CAJZ5v0hAuZmaB6j4qA7P43J4TshBrYa8UsX3KtH7hkxWZPU2wA@mail.gmail.com/T/#t

Cheers!