Re: ia64 acpi-cpufreq driver

[Bjorn Helgaas <bjorn.helgaas@hp.com>]

On Monday 23 October 2006 22:46, Pallipadi, Venkatesh wrote:
> Actually it is slightly different from low_level_read and write. 
> Generic ACPI definition of ACPI PERF_CTRL and PERF_STATUS define 
> them as if they are registers. But, with FfixedHW, ACPI allows 
> architectures to implement this functionality in a native way.
> Just like x86 implements FfixedHW based P-state support in 16 bits 
> of some known MSR (Note the register field itself in _PCT is not used)
> or FFH C-states are supported by native instructions like "hlt",
> "monitor-mwait".
> 
> So, when firmware tells P-state are FFH, OS will look at the hardware 
> and processor information and use appropriate native interfaces. 
> In this case, appropriate native interface is PAL_GET_PSTATE 
> and PAL_SET_PSTATE.

Clearly ia64 ultimately has to use PAL_SET_PSTATE.  My question
is, does the PAL_SET_PSTATE call belong in acpi-cpufreq, or does
it belong in the FFH driver?

I think it belongs in the latter, because the OSPM can be more
generic if the architecture-specific stuff is in the FFH driver.

Another way to ask this is, if ia64 had an FFH driver, who would
use it?  I assume acpi-cpufreq would be one user.  If so, what
interface would acpi-cpufreq use to access FFH?

Bjorn