linux-kernel - Re: [PATCH v6] PM / wakeup: show wakeup sources stats in sysfs

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Message-ID: <CANA+-vDikTE21qOYcvtduqaqPkEaK+8d46A1ReV5VDEZ_O49ww@mail.gmail.com>
Date:   Wed, 31 Jul 2019 16:27:23 -0700
From:   Tri Vo <trong@...roid.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Stephen Boyd <swboyd@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        Ravi Chandra Sadineni <ravisadineni@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>
Subject: Re: [PATCH v6] PM / wakeup: show wakeup sources stats in sysfs

On Wed, Jul 31, 2019 at 4:10 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Aug 1, 2019 at 12:59 AM Tri Vo <trong@...roid.com> wrote:
> >
> > On Wed, Jul 31, 2019 at 3:42 PM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > >
> > > On Thursday, August 1, 2019 12:31:16 AM CEST Tri Vo wrote:
> > > > On Wed, Jul 31, 2019 at 3:17 PM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > > > >
> > > > > On Wednesday, July 31, 2019 11:59:32 PM CEST Stephen Boyd wrote:
> > > > > > Quoting Tri Vo (2019-07-31 14:55:14)
> > > > > > > +/**
> > > > > > > + * wakeup_source_sysfs_add - Add wakeup_source attributes to sysfs.
> > > > > > > + * @parent: Device given wakeup source is associated with (or NULL if virtual).
> > > > > > > + * @ws: Wakeup source to be added in sysfs.
> > > > > > > + */
> > > > > > > +int wakeup_source_sysfs_add(struct device *parent, struct wakeup_source *ws)
> > > > > > > +{
> > > > > > > +       struct device *dev;
> > > > > > > +       int id;
> > > > > > > +
> > > > > > > +       id = ida_alloc(&wakeup_ida, GFP_KERNEL);
> > > > >
> > > > > So can anyone remind me why the IDA thing is needed here at all?
> > > >
> > > > IDA is used to generate the directory name ("ws%d", ID) that is unique
> > > > among wakeup_sources. That is what ends up in
> > > > /sys/class/wakeup/ws<ID>/* path.
> > >
> > > That's not my point (see below).
> > >
> > > > > > > +       if (id < 0)
> > > > > > > +               return id;
> > > > > > > +       ws->id = id;
> > > > > > > +
> > > > > > > +       dev = device_create_with_groups(wakeup_class, parent, MKDEV(0, 0), ws,
> > > > > > > +                                       wakeup_source_groups, "ws%d",
> > > > > >
> > > > > > I thought the name was going to still be 'wakeupN'?
> > > > >
> > > > > So can't we prefix the wakeup source name with something like "wakeup:" or similar here?
> > > >
> > > > "ws%d" here is the name in the sysfs path rather than the name of the
> > > > wakeup source. Wakeup source name is not altered in this patch.
> > > >
> > >
> > > So why wouldn't something like this suffice:
> > >
> > > dev = device_create_with_groups(wakeup_class, parent, MKDEV(0, 0), ws,
> > >                                 wakeup_source_groups, "wakeup:%s", ws->name);
> > >
> > > ?
> >
> > ws->name is inherited from the device name. IIUC device names are not
> > guaranteed to be unique. So if different devices with the same name
> > register wakeup sources, there is an error.
>
> OK
>
> So I guess the names are retained for backwards compatibility with
> existing user space that may be using them?

Yes, in Android we do rely on the name to aggregate statistics across
a fleet of devices. That wouldn't be possible with just the id, as
those are generated at dynamically runtime.
>
> That's kind of fair enough, but having two different identification
> schemes for wakeup sources will end up confusing.

It's not without precedent though. rtc, input, and other devices have
a similar scheme.