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

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Date:	Tue, 22 Sep 2015 10:15:02 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oliver Neukum <oneukum@...e.com>
cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Octavian Purdila <octavian.purdila@...el.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	"Tirdea, Irina" <irina.tirdea@...el.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"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>
Subject: Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing
 runtime suspend

On Tue, 22 Sep 2015, Oliver Neukum wrote:

> Indeed. We can handle output to suspended devices by waking them.
> I don't see why this case is different. We are talking about input
> only.
> 
> > The runtime-PM "usage" value for these devices is a little tricky to 
> > calculate.  It should be nonzero if there are any open files _and_ the 
> > device isn't "inhibited".  I don't know the best way to represent that 
> > kind of condition in the runtime PM framework.
> 
> Does that make sense in the generic framework at all? I still
> think that drivers should cease IO for input in such cases.
> That should involve a common callback, but no counter.

I'm not sure I understand what you're saying.  Are you suggesting that
this "inhibit" mechanism should involve a new callback different from
the existing runtime-PM callbacks?  And when this new callback is
invoked, drivers should cancel existing input requests (these devices
are input-only) and go to low power?

This would create a parallel runtime-PM mechanism which is independent
of the existing one.  Is that really a good idea?

Alan Stern

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