linux-kernel - Re: [PATCH v5] PM / wakeup: show wakeup sources stats in sysfs

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Date:   Tue, 30 Jul 2019 16:31:59 -0700
From:   Tri Vo <trong@...roid.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Stephen Boyd <swboyd@...omium.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        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>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        kbuild test robot <lkp@...el.com>
Subject: Re: [PATCH v5] PM / wakeup: show wakeup sources stats in sysfs

On Tue, Jul 30, 2019 at 4:06 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Wed, Jul 31, 2019 at 12:26 AM Stephen Boyd <swboyd@...omium.org> wrote:
> >
> > Quoting Rafael J. Wysocki (2019-07-30 15:17:55)
> > > On Tuesday, July 30, 2019 8:48:09 PM CEST Stephen Boyd wrote:
> > > > Quoting Tri Vo (2019-07-30 11:39:34)
> > > > > On Mon, Jul 29, 2019 at 10:46 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
> > > > > >
> > > > > > On Tue, Jul 30, 2019 at 4:45 AM Tri Vo <trong@...roid.com> wrote:
> > > > > > > - Device registering the wakeup source is now the parent of the wakeup source.
> > > > > > >   Updated wakeup_source_register()'s signature and its callers accordingly.
> > > > > >
> > > > > > And I really don't like these changes.  Especially having "wakeup"
> > > > > > twice in the path.
> > > > >
> > > > > I can trim it down to /sys/class/wakeup/<ID>/. Does that sound good?
> > > >
> > > > Using the same prefix for the class and the device name is quite common.
> > > > For example, see the input, regulator, tty, tpm, remoteproc, hwmon,
> > > > extcon classes. I'd prefer it was left as /sys/class/wakeup/wakeupN. The
> > > > class name could be changed to wakeup_source perhaps (i.e.
> > > > /sys/class/wakeup_source/wakeupN)?
> > >
> > > Alternatively /sys/class/wakeup/wsN
> > >
> >
> > Or /sys/class/wakeup/eventN? It's your bikeshed to paint.
>
> So actually the underlying problem here is that device_wakeup_enable()
> tries to register a wakeup source and then attach it to the device to
> avoid calling possibly sleeping functions under a spinlock.
>
> However, it should be possible to call wakeup_source_create(name)
> first, then attach the wakeup source to the device (after checking for
> presence), and then invoke wakeup_source_add() (after dropping the
> lock).  If the wakeup source virtual device registration is done in
> wakeup_source_add(), that should avoid the problem altogether without
> having to introduce extra complexity.

This addresses the issue with device_wakeup_enable(), but IIUC we
still have the general problem of multiple devices having the same
name, which leads to name collisions when identifying wakeup sources
with the name only.