linux-kernel - Re: [RFC][PATCH 2/3] PM / sleep: Mechanism to avoid resuming runtime-suspended devices unnecessarily

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Date:	Thu, 15 May 2014 14:55:49 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Linux PM list <linux-pm@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Aaron Lu <aaron.lu@...el.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kevin Hilman <khilman@...aro.org>
Subject: Re: [RFC][PATCH 2/3] PM / sleep: Mechanism to avoid resuming runtime-suspended devices unnecessarily

On Thursday, May 15, 2014 02:06:59 PM Ulf Hansson wrote:
> > Do we want to allow ->prepare() to return > 0 if the device isn't
> > runtime suspended?  If we do then non-suspended devices may be a common
> > case.  We should then avoid the extra overhead of disable + enable.
> > So I would write:
> >
> >         if (dev->power.direct_complete) {
> >                 if (pm_runtime_status_suspended(dev)) {
> >                         pm_runtime_disable(dev);
> >                         if (dev->power.disable_depth == 1
> >                             && pm_runtime_status_suspended(dev))
> >                                 goto Complete;
> >                         pm_runtime_enable(dev);
> >                 }
> >                 dev->power.direct_complete = false;
> >         }
> >
> 
> I am wondering whether the above pm_runtime_disable|enable actually
> belongs better in driver/subsystem in favour of the PM core?

No, it doesn't.

> Doesn't the driver/subsystem anyway needs to be on top of what goes
> on? Typically, while runtime PM has been disabled, that might affect
> it's wakeup handling? Or this case are already handled due to other
> circumstances?

Yes, that's the case.

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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