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

[Guenter Roeck <guenter.roeck@ericsson.com>]

On Tue, Mar 27, 2012 at 03:21:35PM -0400, Björn Gerhart wrote:
> Hi Jean,
> 
> Am 26.03.2012 um 19:01 schrieb Jean Delvare:
> > [..]
> >> If actually it is the job of the module to do such calculations, I would offer to create an it87 patch for IT8783 fixing this - analog to an existing module with a similar behavior (if you know one).
> > 
> > You assume that the PECI value always refers to the CPU. I do not think
> > this is true, other parts (e.g. north bridge) could report their
> > temperature through PECI as well.
> > 
> > And if it is the CPU temperature, we already have the coretemp driver
> > providing the same information, so there's little point in implementing
> > the same in it87. The only benefit of handling PECI sensors in it87 and
> > the like would be so that they can be used as sources for automatic fan
> > speed control, but if the chip itself has no idea about the absolute
> > value of the temperature then I doubt it can use it for automatic fan
> > speed control.
> > 
> Yes, with the coretemp driver even both core temperatures are displayed correctly. So I agree, it's nonsense to implement our special design into the generic driver  ;-)

Depends. As Jean mentioned, it would make sense if the temperature can be used for
automatic fan control.

The PECI specification says (I qoute Wikipedia) "PECI reports a negative value expressing
the difference between the current temperature and the thermal throttle point (at which
the CPU reduces speed or shuts down to prevent damage due to overheating) instead of the
absolute temperature". So the negative value and slope is to be expected.

Question is if there is a way to tell the chip the how to calculate the real temperature
from the raw value reported by PECI. The Nuvoton chips have a set of registers for that
purpose.

Since the raw PECI value is not very useful, it might well be that it is possible
to program the ITE chip to adust its readings. No idea how to do that, though.
If your HW folks have a contact at ITE, maybe you could ask them to try to find out.
Or maybe there is some BIOS code available from ITE and/or from BIOS vendors.

Alternatively, it might be possible to program fan control to take the negative slope
into account; at least Wikipedia suggests that as possibility (to have the fan run faster
as the reported temperature approaches zero from below). No idea how to do that either,
though.

There is also register 0x0a, bits 4-6. Is that set to PECI on your board ?

Either case, I think it would make sense for us to report the sensor type as PECI
if so configured. Yet another patch ...

Thanks,
Guenter

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