RE: [ACPI] Toshiba Sat 3000 with acpi with 20020308

[Diefenbaugh, P. S <pau...@in...>]

Michael:

> I would also appreciate if somebody could explain the difference 
> between throttling and limit (throttling is just x% of the Mhz 
> right?)...

The Limit interface seems to confuse a lot of people ... I probably should
have clarified this a while back!

The concept is to abstract the various forms of processor power management
(throttling, SpeedStep, etc.) into a linear list that can be used by various
policy elements (e.g. thermal policy and power policy) to 'influence'
performance without stomping on each other's feet.  

For example, thermal policy may want to limit (thus the name!) processor
performance to cool a thermal zone at the same time power policy wants to
crank the sucker up to maximum (e.g. just plugged into A/C).  We need a
mechanism to allow the policies to coordinate -- and we do this through
limits.  Each policy sets its limit and the processor driver figures out the
rest.  

Limits can consist of both throttling and performance (e.g. SpeedStep)
states.  For example:
	L0 = P0/T0 (100% performance, 0% throttling = 100% power)
	L1 = P1/T0 (80% performance, 0% throttling = ~50% power)
	L2 = P1/T1 (80% performance, 12.5% throttling = ~44% power)
	 :

Note that the number of performance states may vary dynamically -- another
important reason for the abstraction (so thermal doesn't have to worry about
these details).

Since we haven't implemented SpeedStep support yet, the limit states are
simply a subset of the throttling states.

-- Paul