Re: [lm-sensors] [PATCH] hwmon: (coretemp) Do not return -EAGAIN for low temperatures

[Guenter Roeck <linux@roeck-us.net>]

On 12/21/2013 10:14 AM, Jean Delvare wrote:
> On Fri, 20 Dec 2013 07:53:11 -0800, Guenter Roeck wrote:
>> On Sat, Dec 07, 2013 at 10:05:57AM -0800, Guenter Roeck wrote:
>>> Some Intel CPUs do not set the 'valid' bit in IA32_THERM_STATUS if the
>>> temperature is too low to be measured. This condition will not change until
>>> the CPU is hot enough for its temperature to be measured. Returning an error
>>> in such conditions is not very useful. Drop checking the valid bit and just
>>> return the reported temperature instead.
>>>
>>> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
>>> ---
>>> I don't think we ever closed on this. Giving it a shot.
>>>
>> No feedback. This will go into 3.14 unless there are objections.
>
> I have no objection, I just don't want this change to go to stable, I
> believe it needs a lot of testing on a broad range of hardware before
> we can even think of it.
>
Agreed.

> Reviewed-by: Jean Delvare <khali@linux-fr.org>
>
> On a related note, I think we already noticed that different CPU models
> behave differently in low temperature ranges. As an additional data
> point, I noticed when staring at sensord graphs that my wife's Core2
> Duo E8400 does clamp at 40°C (which is 60°C below Tjmax). It never ever
> reports values below this. Somehow it is a saner implementation than
> clearing the valid bit. Too bad we have no way to represent this in
> sysfs. Would it make sense to define for example tempX_floor (can't
> remember if a better name was ever proposed) so that sensors can report
> "< 40°C" instead of "40°C" in this case? The problem is that I don't
> think these clamp values can be read from a register, I'm not even sure
> if they are documented, so I'm not sure how useful this would be in
> practice...
>

Question is really if we would ever have a chance to determine the value
to report as floor. I suspect the answer is no.

Thanks,
Guenter


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