Re: _CST implementation

[Thomas Renninger <trenn-l3A5Bk7waGM@public.gmane.org>]

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.

     Thomas


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