linux-kernel - Re: [RFC][PATCH 2/2] PM: Make system-wide PM and runtime PM handle subsystems consistently

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Message-ID: <20110217170441.GA31809@kroah.com>
Date:	Thu, 17 Feb 2011 09:04:41 -0800
From:	Greg KH <greg@...ah.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Kevin Hilman <khilman@...com>,
	Grant Likely <grant.likely@...retlab.ca>,
	LKML <linux-kernel@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>,
	Len Brown <lenb@...nel.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [RFC][PATCH 2/2] PM: Make system-wide PM and runtime PM handle
 subsystems consistently

On Thu, Feb 17, 2011 at 09:55:46AM -0500, Alan Stern wrote:
> On Thu, 17 Feb 2011, Rafael J. Wysocki wrote:
> 
> > > > Apart from this I think the order of checks introduced by the $subject patch
> > > > should be:
> > > > (1) If dev->class != NULL and dev->class->pm != NULL, use dev->class,
> > > >     or otherwise
> > > > (2) if dev->type != NULL and dev->type->pm != NULL, use dev->type,
> > > >     or otherwise
> > > > (3) use dev->bus (if present).
> > > > as that would allow classes and device types to override bus type PM
> > > > callbacks if they wish to.
> > > 
> > > I haven't heard of any device types being present on more than one kind
> > > of bus, so it makes sense for device types to override bus types.
> > 
> > OK
> > 
> > > But I'm not so sure about the priority we should give to classes.  On the
> > > other hand, if no classes define a dev_pm_ops then of course it doesn't
> > > matter.
> > 
> > The change will also affect classes that provide "legacy" suspend-resume
> > (if there are any, which I'm totally unsure of).
> > 
> > Anyway, I think we need to choose one ordering. :-)
> > 
> > What about type / bus / class , then?
> 
> I really don't know.  Somebody who has more experience with device 
> class implementations should answer.
> 
> Greg, any ideas?
> 
> To recap: The issue is how to handle multiple PM callbacks.  Since the
> bus type, device type, and device class may all have their own
> callbacks, Rafael has decided the best approach is to prioritize them
> and invoke only the highest-priority callback.  But what priority order
> should we use?

I think we should do it in the following order:
	device type
	device class
	device bus

for the reasons that a device itself could override the default class
and bus information if it "knows" it is special.  After that, the class
of the device holds a lot of information about what is going on with the
logic involved (i.e. network stuff), and lastly, the bus knows some
default hardware information.

Sound reasonable?

I think that follows the default we have today, right?

thanks,

greg k-h
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