Re: [linux-pm] [PATCH] i2c: Use generic subsystem-level power management callbacks

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On Sun, 14 Mar 2010, Rafael J. Wysocki wrote:

> > You know, maybe we should allow bus types to use both the old and new
> > interfaces.  It would make life easier for other subsystems in addition
> > to i2c.
> > 
> > This doesn't mean that the core would end up calling two sets of
> > suspend routines.  If the bus type uses legacy routines then all the
> > non-runtime entries in the pm_ops structure would be empty.
> > 
> > The changes to the PM core necessary to do this are quite small.
> 
> Not really.  The detection that the particular callback is not present happens
> in pm_op(), while the decision which framework to use is made at the
> device_[suspend|resume]() level.

All you have to do is change the "else if" lines in
device_[suspend|resume]() to "if".

> > Does it seem like a reasonable thing to do?
> 
> Well, if someone spends time on implementing new callbacks for a bus type,
> writing them in such a way that they will call the "legacy" callbacks from
> drivers if necessary is not really a big deal IMO.

Sure.  But suppose you _don't_ want to spend the time implementing new
callbacks to replace the existing legacy suspend and resume methods,
whereas you _do_ want to implement runtime PM.  Runtime PM forces the
bus type to have a pm_ops member, which as you point out, will prevent
the legacy methods from being called.

Alan Stern

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