Re: [PATCH] hwmon: (it87) Add support for IT8781F, IT8782F, IT8783E/F

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On Mon, 2012-03-26 at 12:08 -0400, Björn Gerhart wrote:
> Hi Guenter,
> Am 24.03.2012 um 19:07 schrieb Guenter Roeck:
> > On Sat, Mar 24, 2012 at 12:23:13PM -0400, Guenter Roeck wrote:
> >> Hi Bjoern,
> >> 
> >> At 01:11 AM 3/24/2012, Björn Gerhart wrote:
> >> [ ... ]
> >> 
> >>>    label temp3 "CPU T."
> >>>    compute temp3 100+@,-1*(100-@)
> >> 
> >> Is it possible that this is due to a bad sensor type configuration ?
> >> 
> >> Thermal diodes have a "current mode" and a 
> >> "voltage mode", and if misconfigured (or 
> >> miswired) the reported temperature difference is 
> >> just about in that range. Difference in wiring, 
> >> if I understand it correctly, is that the + pin 
> >> is pulled high with a resistor in voltage mode, 
> >> which is not the case in current mode.
> >> 
> As I have learned this morning from our hardware developers, neither "current" nor "voltage" mode is used with temp3, but digital "PECI" mode. In this case, temp3's value describes the _difference_ between the actual temperature and the CPU's maximum temperature (where the CPU will begin to throttle).
> So actually, I think the static sensors.conf is the wrong place to specify this value, because different CPU models have different maximum temperatures. Therefore, dealing with 100 in our own sensors.conf (as implemented by now) is just a very rough inexact value.
> Afaik, only temp3@IT8783 can be used in PECI mode, and in general other ITE sensor chip models can be driven in PECI mode also.
> So, how could the PECI mode be handled on the driver side?
> Detecting if it8783 is in PECI mode:
> - Index register 0x2C, bit 6: set to 1 (Enable PECI)
> - temp3 value is negative until CPU is not throttling
Possibly also register 0x55 (ADC Temperature Extra Channel Enable
Register), bit 7.

Can you check with your HW folks ?


> Where to get current CPU's maximum temperature from:
> - MSR 0x1A2, bit23...bit 16

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