linux-kernel - Re: [PATCH v2 1/2] PM / wakeup: Add callback for wake-up change notification

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Message-ID: <CAMuHMdUYtao4fgQUwBArZG1y+yfbwHE0SHuM6v2NGnhY7GSjkA@mail.gmail.com>
Date:   Tue, 26 Jun 2018 12:29:16 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Mark Brown <broonie@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Marek Vasut <marek.vasut+renesas@...il.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] PM / wakeup: Add callback for wake-up change notification

Hi Rafael,

On Tue, Jun 26, 2018 at 12:17 PM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Tuesday, June 26, 2018 12:06:16 PM CEST Geert Uytterhoeven wrote:
> > On Wed, Jun 20, 2018 at 3:25 PM Mark Brown <broonie@...nel.org> wrote:
> > > On Wed, Jun 20, 2018 at 02:15:38PM +0200, Rafael J. Wysocki wrote:
> > > > On Wed, Jun 20, 2018 at 12:35 PM, Mark Brown <broonie@...nel.org> wrote:
> > >
> > > > > The flip side of that is that either suspend and resume or poweroff are
> > > > > broken for userspace unless they know about this magic sysfs file which
> > > > > isn't great either.
> > >
> > > > But to me that isn't that much different from an RTC wake alarm, say.
> > >
> > > > Enabling it to wake up the system in general isn't sufficient, you
> > > > also need to actually set the alarm using a different interface.
> >
> > The RTC wake alarm time is indeed different, as it is not a simple boolean flag.
> > It is also more natural for the user, who expects to need to find some way to
> > configure the wake-up time.
>
> OK, take Ethernet.  You need to configure WoL on that to wake up the system
> in addition to setting power/wakeup for it.
>
> Take WiFi: You need to set up WoW on that.
>
> And so on.

I always found it strange that you have both "ethtool wol" and and a
"wakeup" file
in sysfs (does "ethtool wol" predate the wakeup file in sysfs?)

I believe originally WoL supported MagicPacket only (many systems still
support only that), so originally it was boolean.

> > > It seems more like hardware breakage we're trying to fix than a feature
> > > - it's not like it's adding something we didn't have already (like
> > > setting a time in an alarm where the alarm is an additional thing), more
> > > just trying to execute on an existing user interface successfully.  I
> > > can see that there's a case that it doesn't map very well onto the
> > > standard interfaces so perhaps we have to add something on the side as
> > > the hardware is just too horrible to fit in with the standard interfaces
> > > and we have to do that.
> >
> > My main worry is usability: with a separate sysfs file, we need to document the
> > file, and the user needs to be aware of it.
>
> That's right, but it will be very hard to convince me that changing the
> meaning of the "wakeup" attribute just in order to work around this issue
> (which arguably is a consequence of "unfortunate" hardware design) is a
> good idea. :-)

OK.

Next question: where to document device-specific sysfs files for regulators?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds