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

["Rafael J. Wysocki" <rjw-KKrjLPT3xs0@public.gmane.org>]

On Saturday 13 March 2010, Alan Stern wrote:
> On Sat, 13 Mar 2010, Rafael J. Wysocki wrote:
> 
> > Please note that the "legacy" callbacks removed by this patch are already
> > effectively dead, because they are not going to be called by the PM core
> > anyway.  I'm not sure if this is what we want, though, so please let me know
> > in case it's not.
> 
> 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.

> 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.

The problem in this particular case is that I don't know whether or not we
_want_ the drivers' "legacy" callbacks to be invoked at all.  The $subject
patch assumes we don't, but if we do in fact, I'll rework it to do so.

I need that piece of information, though. :-)

Rafael