Re: _CST implementation

[Bruno Ducrot <ducrot-kk6yZipjEM5g9hUCZPvPmw@public.gmane.org>]

On Tue, Apr 19, 2005 at 01:58:09PM +0200, Thomas Renninger wrote:
> Bruno Ducrot wrote:
> > On Mon, Apr 18, 2005 at 07:25:54PM +0200, Thomas Renninger wrote:
> >>Bruno Ducrot wrote:
> >>>On Fri, Apr 15, 2005 at 10:50:44PM +0200, Janosch Machowinski wrote:
> >>...
> >>>>Oh I almost forgot another question : 
> >>>>About the validation of the C states. At the moment it is tested if the
> >>>>latency of C2 if under 100 and if C3 latency is under 1000 but the
> >>>>ACPI-Spec says that "There is no latency restrictions" so why do you do
> >>>>this ? (My notebook hat a C3 latency of 1001)
> >>>Normally you are right, but unfortunately there are still some strange
> >>>misread of the specification by bios writters in that regard.  Therefore
> >>>if for C3 the latency is 1001 even if given by _CST, we should disable
> >>>it.
> >>>
> >>My spec says (Revision 3.0, September 2, 2004):
> >>The worst-case hardware latency for this state is declared in the FADT
> >>(p. 257).
> >>
> >>And there they say (p. 98):
> >>The worst-case hardware latency, in microseconds, to enter and
> >>exit a C2 state. A value > 100 indicates the system does not
> >>support a C2 state.
> >>The worst-case hardware latency, in microseconds, to enter and
> >>exit a C3 state. A value > 1000 indicates the system does not
> >>support a C3 state.
> >>
> > 
> > For P_LVL2_LAT and P_LVL3_LAT defined in the FADT only.  There are no
> > such restriction if _CST exist (see 8.1.5 and 8.4.2).
> > If power states are defined via _CST, then all of them are valid.
> > 
> 
> Thanks, only knew of the fadt restrictions.
> This should fix it?
> Only compile tested.

There is this problem:
> >>>Normally you are right, but unfortunately there are still some strange
> >>>misread of the specification by bios writters in that regard.  Therefore
> >>>if for C3 the latency is 1001 even if given by _CST, we should disable
> >>>it.

IOW, from spec we should not invalidate, but from "common practice" by
bios writters, we should invalidate.

-- 
Bruno Ducrot

--  Which is worse:  ignorance or apathy?
--  Don't know.  Don't care.


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