Re: [PATCH v2] hwmon: (ntc_thermistor): try reading processed

[Linus Walleij <linus.walleij@linaro.org>]

On Thu, Dec 24, 2020 at 4:15 AM Chris Lesiak <chris.lesiak@licor.com> wrote:

> A closer reading of the "iio: inkern: pass through raw values if no scaling"
> commit leads me to believe that even when the sensor provides no scale,
> the returned value is expected to be in the correct units.
>
> If that is true, there was a bug in the commit.
> It failed to apply the caller supplied scale that ntc_thermistor.c relies on
> to convert from milliVolts to microVolts.
>
> Linus, would this change address your original problem?
>
> diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c
> index fe30bcb6a57b..79787474d511 100644
> --- a/drivers/iio/inkern.c
> +++ b/drivers/iio/inkern.c
> @@ -587,7 +587,7 @@ static int iio_convert_raw_to_processed_unlocked(struct iio_channel *chan,
>                  * Just pass raw values as processed if no scaling is
>                  * available.
>                  */
> -               *processed = raw;
> +               *processed = raw * scale;
>                 return 0;
>         }

I do not think the raw values have any obligation to be in
e.g. millivolts. They may be, by chance.

In my case, it is just an unscaled byte [0..255].

So it unfortunately does not solve my problem, because in my driver,
that does not support scaling, the result will be the raw value
* 1000 which is not going to be microvolts at all, because the
raw values are not millivolts, rather a value 0..255.

However if I used the processed values, the value will be
adjusted non-linearly to millivolts.

Yours,
Linus Walleij