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

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Message-ID: <CANA+-vCoCuMtSKCfnav9NSwrzX7of9iLbppNX+pcymBp19kgQQ@mail.gmail.com>
Date:   Thu, 1 Aug 2019 12:50:25 -0700
From:   Tri Vo <trong@...roid.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.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>,
        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 4:45 PM Stephen Boyd <swboyd@...omium.org> wrote:
>
> Quoting Rafael J. Wysocki (2019-07-31 16:10:38)
> > 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:
> > > >
> > > > 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?
> >
> > That's kind of fair enough, but having two different identification
> > schemes for wakeup sources will end up confusing.
>
> I understand your concern about the IDA now. Thanks for clarifying.
>
> How about we name the devices 'wakeupN' with the IDA when they're
> registered with a non-NULL device pointer and then name them whatever
> the name argument is when the device pointer is NULL. If we have this,
> we should be able to drop the name attribute in sysfs and figure out the
> name either by looking at the device name in /sys/class/wakeup/ if it
> isn't 'wakeupN', or follow the symlink to the device in /sys/devices/
> and look at the parent device name there.

This makes it difficult for userspace to query the name a wakeup
source, as it now has to first figure out if a wakeup source is
associated with a device or not. The criteria for that is also
awkward, userspase has to check if directory path contains "wakeupN",
then it's a virtual wakeup source.

IMO it's cleaner to consistently have /sys/class/wakeup/wakeupN/name
for every wakeup source.