linux-kernel - Re: [PATCH v3 1/2] PM / sleep: Let devices force direct

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Date:	Fri, 17 Apr 2015 13:30:35 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
cc:	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	<linux-pm@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] PM / sleep: Let devices force direct_complete

On Fri, 17 Apr 2015, Laurent Pinchart wrote:

> Hi Tomeu,
> 
> Thank you for the patch.
> 
> On Friday 17 April 2015 17:24:49 Tomeu Vizoso wrote:
> > Introduce a new per-device flag power.force_direct_complete that will
> > instruct the PM core to ignore the runtime PM status of its descendants
> > when deciding whether to let this device remain in runtime suspend when
> > the system goes into a sleep power state.
> > 
> > This is needed because otherwise it would be needed to get dozens of
> > drivers to implement the prepare() callback and be runtime PM active
> > even if they don't have a 1-to-1 relationship with a piece of HW.
> 
> I'll let PM experts comment on the approach, but I believe the new flag would 
> benefit from being documented (likely in Documentation/power/devices.txt) :-)

Documentation/power/runtime_pm.txt is the right place.

However, I'm not sure that this is the sort of thing Rafael meant when 
he suggested adding a new flag.  I thought he meant the PM core would 
look at the new flag only if there was no ->prepare method at all.  
Then if the new flag was set, the PM core would act as though ->prepare 
had returned 1.  That way there would be no need to add silly little
one-line *_prepare() routines all over the place.

Maybe he had something else in mind, though...

Alan Stern

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