patch: p4tcc and speedstep cpufreq drivers

[Nate Lawson]

Maxim Sobolev wrote:
> Kevin Oberman wrote:
>> No joy. I set it to 262 and it was fine. The next step killed the system
>> again.
>>
>> I'm also concerned that taking TCC out of automatic mode might not be a
>> great idea, at least until things like _PSV are supported. When I do a
>> buildkernel, buildworld or any big compile job, I need to slow down the
>> CPU to keep the CPU form frying. It quickly jumps to 185 F. or higher if
>> I don't. If I understand automatic TCC, it should throttle the CPU all
>> by itself to prevent this.
> 
> 
> Taking TCC out of automatic mode doesn't disable thermal controlling 
> circuitry completely, so that if the processor overheats it will shut 
> down the machine anyway:
> 
> ---
> Regardless of enabling of the automatic
> or On-Demand modes, in the event of a catastrophic cooling failure, the 
> processor will
> automatically shut down when the silicon has reached a temperature of 
> approximately
> 135 °C. At this point the system bus signal THERMTRIP# will go active 
> and stay active
> until RESET# has been initiated. 
> ---

Correct.  Even more so, automatic mode continues to override On-Demand 
mode if there is a more moderate thermal condition than THERMTRIP#:

"On-Demand mode may be used at the same time Automatic mode is enabled, 
however, if the system tries to enable the TCC via On-Demand mode at the 
same time automatic mode is enabled AND a high temperature condition 
exists, the duty cycle of the automatic mode will override the duty 
cycle selected by the On-Demand mode."

Since automatic mode is set by the BIOS before we even boot, things 
should be fine.

>> Between throttling and frequency adjustment I can get about 16
>> performance levels and I don' see a good reason for another 15. Also,
>> the change is frequency is so non-linear that small changes often don't
>> make sense. The first three step are fairly straight, but then things
>> get bumpy. It looks to me like all frequency settings are not created
>> equal. 
> 
> I wonder this too. I think in the presence of several independent 
> regulators we need some form of calibration to get more or less precise 
> results.

You can manually test this kind of stuff by doing:
hint.p4tcc.0.disabled="1"

-- 
Nate