linux-kernel - Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing runtime suspend

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Date:	Wed, 9 Sep 2015 11:22:27 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Tirdea, Irina" <irina.tirdea@...el.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Brown, Len" <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	"Purdila, Octavian" <octavian.purdila@...el.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing
 runtime suspend

On Tue, 8 Sep 2015, Rafael J. Wysocki wrote:

> Hi,
> 
> On Tue, Sep 8, 2015 at 5:00 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> > On Tue, 8 Sep 2015, Rafael J. Wysocki wrote:
> >
> >> > > [1] http://marc.info/?l=linux-input&m=140564626306396&w=2
> >> >
> >> > Purely as a matter of interest, in that email Rafael also mentioned
> >> > that he and I had discussed a way to disable remote wakeup during
> >> > runtime suspend.  Oddly enough, the method we decided upon was to add
> >> > an "off" option to /sys/.../power/control.  :-)
> >>
> >> Wasn't that /sys/devices/.../power/wakeup rather?
> >
> > Not the way I remember.  Of course, it's possible that we misunderstood
> > each other at the time.
> >
> >> > It would not put the device into runtime suspend immediately, like you
> >> > are proposing.  Instead it would mean the same as the "auto" mode,
> >> > except that remote wakeup should be disabled during runtime suspend.
> >> >
> >> > We never got around to implementing this, however.
> >>
> >> I don't think this is what we discussed then really.
> >>
> >> There is a fundamental problem with forcing things into runtime suspend
> >> from user space, because that may happen in a wrong time.  In other words,
> >> the kernel can't guarantee that the device would actually be able to go
> >> into runtime suspend when requested.
> >
> > Exactly.  What we discussed at LinuxCon wasn't forcing things into
> > runtime suspend; it was disabling remote wakeup during runtime suspend.
> >
> > And even though the topic was quite different from Irina's proposal, we
> > ended up settling on the same API (according to my recollection).
> 
> So I remember that differently.
> 
> My idea was to add a third value to /sys/devices/.../power/wakeup (in
> addition to "disabled" and "enabled") so user space can indicate that
> remote wakeup should not be enabled for runtime suspend for the device
> (since there's no way to indicate that today).  I don't see how
> /sys/devices/.../power/control might help here to be honest.

You're right, that does make more sense than what I was thinking.  My 
memory must have gotten messed up.  RAM corruption, no doubt...  I 
think I need an EDAC brain.  :-)

Alan Stern

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