CPU C-state storange on Panasonic TOUGH BOOK CF-R9

[Andriy Gapon]

on 12/09/2010 19:00 Alexander Motin said the following:
> 
> I am not sure this patch is complete:

Well, I agree, it's far from complete.  And situation is somewhat messy.

> 1) AFAIR I have seen somewhere example where system had several C-states
> with different latency, but the same type - C3. Type only means
> enter/exit semantics, and there could be several states with the same
> semantics. Not sire how to properly them in this case.

ACPI specification suggests how to address this, but I am not sure if we want to
follow that suggestion and how we would do that:

ACPI> Notice in the example above that OSPM should anticipate the possibility of a
_CST object providing more
ACPI> than one entry with the same C_State_Type value. In this case OSPM must
decide which C_State_Register
ACPI> it will use to enter that C state.

So it looks like the specification does tie C_State_Type to "C state".
But then, in general, the specification looks confusing.  It mentions C4, ..., Cn
states; but then says that their enter/exit semantics should correspond to C1, C2,
C3; but then it uses "1, 2, 3, *etc*" [emphasis mine] when it describes C State type.
So, at least I am confused as to what they would designate with C4 - a state
described in _CST with type of 4, or a forth state in _CST perhaps with a type of
3.  And entry/exit semantics the state would have in the former case.
I do not see an explicit answer in their wording.

> May be existing
> approach was not so bad. It is ACPI C-states, not CPU C-states, they are
> not same.
> May be we should just mention type somewhere in addition.
> 2) This change makes heavily understandable values of cx_lowest.
> 3) If touch cx_lowest, I would prefer to see there possibility to set it
> to some abstract C6 or whatever, allowing system automatically choose
> state it has available at the moment.
> 

Yes, I agree.  It's just overall confusing.
But you are correct that index of a C-state works better than "C-state-type" or
whatever it can be called.  And a user probably doesn't care much about the
latter.  But probably it's a good idea to report the type somewhere.

I am also going to take a look how Linux and OpenSolaris name the C-states.
-- 
Andriy Gapon