Re: Re: Platform-specific system power states

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Saturday, 23 June 2007 03:32, Alan Stern wrote:
> On Fri, 22 Jun 2007, Rafael J. Wysocki wrote:
> 
> > On Friday, 22 June 2007 21:49, David Brownell wrote:
> > > On Thursday 21 June 2007, Alan Stern wrote:
> > > > 
> > > > I'd be perfectly happy to have the list of supported system power 
> > > > states be exported by the platform code instead of predetermined by the 
> > > > PM core.  It would still be necessary to add a method whereby the PM 
> > > > core could inform the platform about the new target state at the 
> > > > beginning of a state change.  And of course there would have to be a 
> > > > way for drivers or subsystems to query the platform, to see what 
> > > > resources would be available.
> > > 
> > > Rafael will propose the new method, I guess;
> > 
> > Yes, I will.
> > 
> > Still, for now, I'm going to make it take an integer argument equal to either
> > PM_SUSPEND_STANDBY or PM_SUSPEND_MEM, since these are the only two sleep states
> > known to the core right now.
> > 
> > I think, however, that in the long run the better solution would be to make
> > the platform tell the PM core, during the initialization, what system sleep
> > states are available.  Then, before the transition, the PM core will tell the
> > platform which state is the target one.  IMO for this purpose the sleep will
> > need to be identified in a universal way and perhaps it's a good idea to
> > discuss that for a while. ;-)
> 
> A good way to identify a sleep state would be a pointer to a string 
> containing the state's name.  The PM core could use these pointers to 
> export the states in sysfs.

Well, I thought of exactly the same thing.

Perhaps we can generalize it a bit by defining:

struct pm_sleep_state {
	char *name;
};

and make the platforms give us a NULL-terminated array of such things during
the initializatiion.

Then, if it turns out to be convenient to add another field to this structure,
there won't be any problems with that.  Also, the platforms will be able to
embed a struct pm_sleep_state in their internal structures representing system
sleep states, if need be.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth