RE: ia64 acpi-cpufreq driver

From: Pallipadi, Venkatesh <>
Date: 2006-10-25 09:59:24

>-----Original Message-----
>From: Bjorn Helgaas [] 
>Sent: Tuesday, October 24, 2006 10:51 AM
>To: Pallipadi, Venkatesh
>Subject: Re: ia64 acpi-cpufreq driver
>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 
>> and processor information and use appropriate native interfaces. 
>> In this case, appropriate native interface is PAL_GET_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?

Yes. As it is today, acpi-cpufreq contains FFH driver functionality 
in itself. It calls acpi and cpufreq arch-independent interfaces but 
implements FFH internally. 

By, FFH driver do you mean to handle FFH related functions only for 
P-states or something that can handle all FFH functions (like C-states,
I don't see any other kernel part/or driver will use this particular 
PAL_GET_PSTATE and PAL_SET_PSTATE intefaces. So, my feeling is we don't
need a separate FFH driver.

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Received on Wed Oct 25 09:59:56 2006

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