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

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Message-ID: <2125433.CLuFqMxLgc@vostro.rjw.lan>
Date:	Tue, 08 Sep 2015 17:15:42 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"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 Tuesday, September 08, 2015 10:44:04 AM Alan Stern wrote:
> On Tue, 8 Sep 2015, Tirdea, Irina wrote:
> 
> > In the previous discussion thread , there were a couple of options
> > mentioned, but none seemed to reach a consensus. You mentioned
> > adding a "more aggressive runtime PM mode" [1]. I'm not sure how
> > this would work except for adding a sysfs attribute that would trigger
> > a runtime suspend while ignoring usage count. Would that be a
> > better direction?
> > 
> > Thank you,
> > Irina
> > 
> > [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?

> 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.

Thanks,
Rafael

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