Re: [RFC 0/3] Runtime PM support for named power states

[David Brownell <david-b@pacbell.net>]

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On Wednesday 05 October 2005 12:44 am, Adam Belay wrote:
> On Tue, Oct 04, 2005 at 11:04:35PM -0700, David Brownell wrote: 
> > 
> > The PM core should just tell drivers to become compatible with some
> > new constraint (like ACPI S3, generally implying devices in PCI D2
> > or D3; while S1 doesn't) ... and not worry about whether that involves
> > a state change or not.
> > 
> > Maybe they're already _in_ that state for example.
> 
> Yeah, the thought occurred to me.  One way of approaching the problem is to
> have the PM core use logical states such as the following:
> 
> 1.) ON
> 2.) FREEZE
> 3.) SUSPEND
> 
> others?
> 
> This is similar to our current implementation.

Which is a problem, as I've described before.  The logical states
must be system-specific.  Some systems have more states than just
those three ... and in particular, the states have ** SOLID **
and ** PRECISE ** definitions.  Unlike those three.

At the risk of sounding like a broken record, I'll give the
same example I've given before:  some states may not support
particular clocks, like the 48 MHz USB clock.  So the driver
needs to know which ** PRECISE ** system-specific state is
being entered ... so it can turn off the clock if need be.

- Dave

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