Re: [PATCH v2 12/16] hwmon: (mr75203) modify the temperature equation

Farber, Eliav
2022-08-19T07:44:34Z

On 8/18/2022 11:23 PM, Guenter Roeck wrote:
> On Wed, Aug 17, 2022 at 05:43:17AM +0000, Eliav Farber wrote:
>> Modify the equation and coefficients to convert the digital output to
>> temperature according to series 5 of the Moortec Embedded Temperature
>> Sensor (METS) datasheet:
>> T = G + H * (n / cal5 - 0.5) + J * F
>>
>> The G, H and J coefficients are multiplied by 1000 to get the
>> temperature
>> in milli-Celsius.
>>
>
> This is, at the very least, confusing. It doesn't explain the discrepancy
> to the old code nor the change in constant values. I have no idea if this
> change would result in erroneous readings on some other system where
> the existing calculation may be the correct one.

When I tested the driver it was also not clear to me why the equation
and coefficients in the code don't match the specifications in the data
sheet.
I reached out to Maxlinear engineers (@rtanwar) and they also couldn't
explain the discrepancy.
After further correspondence I aligned both the equation and coefficients
in the driver code to the equation and coefficients defined in series 5
of the Moortec Embedded Temperature Sensor (METS) datasheet which they
provided.

> On top of that, it seems overflow-prune in 32 bit systems.

I'll check if it can overflow, and if it can I'll fix in next version.

--
Regards, Eliav