linux-kernel - Re: Intel Core2Duo mobile - how does the VID get set?

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Message-id: <47BB6BD6.1090105@shaw.ca>
Date:	Tue, 19 Feb 2008 17:52:54 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Brian Morrison <bdm@...rir.org.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Intel Core2Duo mobile - how does the VID get set?

Brian Morrison wrote:
> Pallipadi, Venkatesh wrote:
> 
>>> After a fair bit of Googling and reading around, I'm none the wiser 
>>> about exactly how Linux 2.6.x sets the processor VID (or for that 
>>> matter how it decides the FID settings) when using the ondemand 
>>> governor and cpufreq stuff.
>>>
>>> Can anyone tell me a) whether this is obtained from the BIOS, 
>>> something in the MSR of the processor or elsewhere and
>>
>> Yes. The freq and voltage supported comes from the platform BIOS. BIOS
>> exports this in an ACPI table which is handled by acpi-cpufreq driver in
>> Linux kernel.
>>
> 
> OK, thanks for that.
> 
>>  
>>> b) whether there is an interface in /proc or /sys where one can find 
>>> out what is set and modify it?
>>
>> There is no way of modifying and using new VIDs etc in Linux kernel
>> (other than exporting your own DSDT and hacking the related code).
> 
> Is there a way of viewing the ACPI table contents relating to the VIDs
> and FIDs?

Viewing the decompiled ACPI DSDT may provide some hints, however the 
kernel itself knows nothing about VID/FID settings for acpi-cpufreq, 
basically the kernel writes to magic ACPI registers and the BIOS or 
hardware take over to do what's required..
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