Re: [RFC][PATCH] Power domains for platform bus type

[Grant Likely <grant.likely@secretlab.ca>]

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.  ie. it is conceivable that some spi and i2c devices would be in
need to be in the same power_domain.

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.

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.

g.