Re: [linux-pm] calling runtime PM from system PM methods

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On Thu, Jun 09, 2011 at 09:56:48AM -0400, Alan Stern wrote:
> On Wed, 8 Jun 2011, Kevin Hilman wrote:

> > Runtime suspend
> > 2. activity finishes

> > system suspend [echo mem > /sys/power/state]
> > 2. prevent future activity, halt/wait for current activity

> > The only difference is step 2.

> That _is_ the main difference, and it's a big one.  (As Magnus pointed 
> out, wakeup-enabling is another difference).

...

> They don't have to be decoupled, and indeed they can share code.  The 
> point Rafael and I are making is that they have to use different 
> callback pointers, which gives you a chance to handle the differences 
> as well as the similarities.

It seems like everyone's agreeing with each other here - from the user
side the request seems to be largely for core infastructure like
UNIVERSAL_DEV_PM_OPS() (which I'm not sure is a good idea any more given
that it doesn't do anything to handle the runtime/system interaction?).
Right now this all feels like more work than it should be in simpler
drivers.

> > For many (if not all) devices though, what I suspect we would want is
> > for devices that are runtime suspended to stay runtime suspended across
> > a system suspend *and* resume.  That would mean that the device power
> > domain would not call system PM callbacks on devices that are runtime
> > suspended.

> No, it's generally agreed that _all_ devices should return to full 
> power during system resume -- even if they were runtime suspended 
> before the system sleep.  This also is explained in the Documentation 
> files.

What is the reasoning behind this agreement?  It's not immediately
obvious why this is useful.
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