linux-kernel - Re: "PM / wakeup: Show wakeup sources stats in sysfs" causes boot warnings

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Date:   Wed, 14 Aug 2019 11:37:05 -0700
From:   Tri Vo <trong@...roid.com>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Stephen Boyd <swboyd@...omium.org>, Qian Cai <cai@....pw>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: "PM / wakeup: Show wakeup sources stats in sysfs" causes boot warnings

On Wed, Aug 14, 2019 at 1:40 AM Tony Lindgren <tony@...mide.com> wrote:
>
> * Stephen Boyd <swboyd@...omium.org> [691231 23:00]:
> > I also notice that device_set_wakeup_capable() has a check to see if the
> > device is registered yet and it skips creating sysfs entries for the
> > device if it isn't created in sysfs yet. Why? Just so it can be called
> > before the device is created? I guess the same logic is handled by
> > dpm_sysfs_add() if the device is registered after calling
> > device_set_wakeup_*().
>
> Hmm just guessing.. It's maybe because drivers can enable and disable
> the wakeup capability at any point for example like driver/net drivers
> do based on WOL etc?
>
> > There's two approaches I see:
> >
> >       1) Do a similar check for device_set_wakeup_enable() and skip
> >       adding the wakeup class until dpm_sysfs_add().
> >
> >       2) Find each case where this happens and only call wakeup APIs
> >       on the device after the device is added.
> >
> > I guess it's better to let devices have wakeup modified on them before
> > they're registered with the device core?
>
> I think we should at least initially handle case #1 above as multiple
> places otherwise seem to break. Then maybe we could add a warning to
> help fix all the #2 cases if needed?

Makes sense. For case#1, we could also just register the wakeup source
without specifying the parent device if the latter hasn't been
registered yet. Userspace won't be able to associate a wakeup source
to the parent device. But I think it's a reasonable fix, assuming we
want to fix devices not being added before calling wakeup APIs #2.