linux-kernel - Re: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled and device suspended.

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Date:	Fri, 20 Jun 2014 10:48:09 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
cc:	Kevin Hilman <khilman@...aro.org>, Allen Yu <alleny@...dia.com>,
	Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled
 and device suspended.

On Fri, 20 Jun 2014, Rafael J. Wysocki wrote:

> > For a general device, the fact that dev->power.is_suspended is set
> > means the device _has_ been powered down.  Even though the
> > runtime_status may not have changed, the PM core has to assume the
> > device is not available for use.
> 
> This seems to go a bit too far.  What power.is_suspended actually means is
> that __device_suspend() has run for the device successfully.  What the
> implications of that are depends on the bus type (or subsystem in general)
> and device driver.
> 
> > While your I2C devices may be useable even after the ->suspend callback
> > returns, for most devices this isn't true.  So we shouldn't allow
> > rpm_resume() to return imediately when is_suspended is set.
> 
> I can agree with that.

We really do need to decide more precisely how runtime PM and system PM 
will interact.  Should ->runtime_resume callbacks be allowed after 
->suspend has returned?

Kevin has stated that some devices do need this ability.  But most
don't.  The PM core needs to handle these conflicting requirements
somehow.

Note: this is a separate issue from the meaning of disabled_depth > 0.

Alan Stern

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