On Monday, January 31, 2011, Grant Likely wrote:
> On Sun, Jan 30, 2011 at 01:07:19AM +0100, Rafael J. Wysocki wrote:
> > Hi,
> >
> > This is something we discussed during the last Linux Plumbers Conference.
> >
> > The problem appears to be that the same device may be used in different
> > systems in different configurations such that actions necessary for the
> > device's power management can vary from one system to another. In those
> > cases the drivers' power management callbacks are generally not sufficient,
> > because they can't take the configuration of the whole system into account.
> >
> > I think this issue may be addressed by adding objects that will represent
> > power domains and will provide power management callbacks to be executed
> > in addition to the device driver's PM callbacks, which is done by the patch
> > below.
> >
> > Please have a look at it and tell me what you think.
>
> In general it looks okay. I agree with Alan's comment that it
> probably belongs outside the platform device pm ops. It's the sort of
> thing that should be available to *any* device, regardless of bus
> type.
I'd rather say any subsystem. Anyway, I'm not sure how many subsystems
will find it useful at the core level except for platform.
> ie. it is conceivable that some spi and i2c devices would be in
> need to be in the same power_domain.
So there's spi and i2c. Anything else?
> It slightly worries me about the amount of code required to manage all the
> nested levels of pm_ops. I wonder if there is a better way to manage
> them.
I'm not really sure. The amount of code is kind of proportional to the
number of different callbacks in struct dev_pm_ops ...
> Also, what is the use case for having 2 sets of power_domain ops? My
> gut tells me that you'd only want to do post ops on the
> {freeze,suspend,poweroff} path and pre ops on the {resume,thaw,restore}
> path. It seems overly engineered to me, but I may be missing
> something fundamental.
Well, that's a part of the RFC, actually. :-)
For the subsystems I've worked with (PCI, ACPI, PNP to some extent) one set
would be sufficient, but I don't know of every possible use case.
Thanks,
Rafael
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