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

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Date:	Fri, 25 Sep 2015 22:15:28 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Oliver Neukum <oneukum@...e.de>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Irina Tirdea <irina.tirdea@...el.com>,
	Len Brown <len.brown@...el.com>,
	Octavian Purdila <octavian.purdila@...el.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Pavel Machek <pavel@....cz>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing runtime suspend

On Friday, September 25, 2015 10:29:55 AM Alan Stern wrote:
> On Fri, 25 Sep 2015, Rafael J. Wysocki wrote:
> 
> > We are missing the "no remote wakeup" bit now (well, there is a PM QoS flag,
> > but it isn't very useful, so I'd prefer to replace it with a "no remote wakeup"
> > bit in struct dev_pm_info or something similar).
> > 
> > That is actually quite important, because (a) we can save energy but not
> > configuring the device to do remote wakeup in the first place and (b) that
> > may involve more than just the driver (for example, disabling PCI or ACPI
> > remote wakeup involves the bus type or similar).
> > 
> > So it looks like we need to be able to distinguish between "runtime suspend
> > with remote wakeup" and "runtime suspend without remote wakeup".
> > 
> > And if we do the latter, we may not even need the "inhibit" thing any more,
> > because suspended devices without that are not configured to do remote wakeup
> > cannot really signal anything in the majority of cases.
> 
> That works only for drivers that use autosuspend to go to low power in
> between events.  It doesn't work for drivers that remain at full power 
> as long as the device file is open.  That kind of driver does require 
> an "inhibit" interface.

Or an interface allowing user space to trigger pm_request_idle() for them.

So user space would change the "no remote wakeup" setting and then do the
"try to suspend now" thing.

Thanks,
Rafael

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