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

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Date:   Fri, 16 Aug 2019 14:17:23 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Tri Vo <trong@...roid.com>
Cc:     Tony Lindgren <tony@...mide.com>,
        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 8:37 PM Tri Vo <trong@...roid.com> wrote:
>
> 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.

Well, OK

I'm going to drop the entire series from linux-next at this point and
let's start over.

Also note that all of this is not an issue until we start to add
children under the device passed to device_set_wakeup_enable() and
friends so maybe that is not a good idea after all?