acpi_cpu: _PDC vs _OSC

[Rui Paulo]

On 3 Feb 2010, at 14:53, Andriy Gapon wrote:

> 
> What do you think about changing logic of evaluating _PDC and _OSC for Processor
> object in acpi_cpu_attach?
> It seems that later versions of ACPI standard deprecate _PDC in favor of _OSC.
> Although, in practice they seem to be present or not present together, sometimes
> _PDC being only a wrappper around _OSC.  There are still, of course, systems with
> only _PDC present.  I assume that there are systems with only _OSC too.
> 
> I would like to change the order, so that _OSC evaluation is attempted first and
> only if it fails then proceed with _PDC.
> 
> Also, I would like to print status returned by _OSC (in case of successful
> evaluation) if it is not zero. (Note: this is not the same as status of evaluating
> _OSC).
> 
> And I am going to fix the following comment:
> * On some systems we need to evaluate _OSC so that the ASL
> * loads the _PSS and/or _PDC methods at runtime.
> 
> Although on many systems either _PDC or _OSC or both dynamically load SSDTs that
> contain additional Processor objects like _PSS and _PCT, I haven't seen any system
> where _OSC would load _PDC.  And, honestly, that wouldn't make any sense.
> Perhaps, comment's author meant _PCT in place of _PDC, or something like that.

I added the comment and I have such system. It's a MacBook first generation.

By evaluating _OSC we were able to make _PDC visible, thus enabling cpufreq(4).

--
Rui Paulo