RE: [Xen-devel] cpufreq support status

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Jan Beulich
>Sent: 2007年10月24日 16:28
>
>Looking into this some more, I find that
>ACPI_ADR_SPACE_FIXED_HARDWARE
>is mostly unsupported in Linux except for C-state handling, in which case
>is
>resolves to MWAIT.
>

FFH is mapped to msr for P-state handling on Intel processors. You 
can refer to acpi-cpufreq.c in latest native Linux kernel, where have 
logic to handle both IO space and FFH space.

Since 2.6.2*, acpi-cpufreq.c is the preferred cpufreq driver for 
intel processors.

But if you look at the current 2.6.18-xen, acpi-cpufreq.c can only handle 
I/O space and instead speedstep-centrino.c manipulates FFH, i.e. MSR 
directly. But because the _PDC capabilities is set to FFH capable in 
2.6.18, speedstep_centrino.c becomes the only drive working in this 
environment then.

Thanks,
Kevin

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