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SubjectRe: [PATCH v2 7/8] iio: afe: rescale: add temperature sensor support
From
Date
Hi!

On 2021-06-07 16:47, Liam Beguin wrote:
> From: Liam Beguin <lvb@xiphos.com>
>
> Add support for linear temperature sensors. This is meant to work with
> different kinds of analog front ends such as RTDs (resistance
> thermometers), voltage IC sensors (like the LTC2997), and current IC
> sensors (see AD590).
>
> Signed-off-by: Liam Beguin <lvb@xiphos.com>
> ---
> drivers/iio/afe/iio-rescale.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
> index 3d445c76dbb2..9e3c7e2b47cd 100644
> --- a/drivers/iio/afe/iio-rescale.c
> +++ b/drivers/iio/afe/iio-rescale.c
> @@ -272,10 +272,29 @@ static int rescale_voltage_divider_props(struct device *dev,
> return 0;
> }
>
> +static int rescale_temp_sense_amplifier_props(struct device *dev,
> + struct rescale *rescale)
> +{
> + s32 gain_mult = 1;
> + s32 gain_div = 1;
> + s32 offset = 0;
> +
> + device_property_read_u32(dev, "sense-gain-mult", &gain_mult);
> + device_property_read_u32(dev, "sense-gain-div", &gain_div);
> + device_property_read_u32(dev, "sense-offset-millicelsius", &offset);
> +
> + rescale->numerator = gain_mult;
> + rescale->denominator = gain_div;
> + rescale->offset = offset * gain_div / gain_mult;

This should be done with 64-bit math, no? After all, An offset of
approximately 300000 is not unexpected, and that's quite big to
scale with 32-bit math.

Cheers,
Peter

> +
> + return 0;
> +}
> +
> enum rescale_variant {
> CURRENT_SENSE_AMPLIFIER,
> CURRENT_SENSE_SHUNT,
> VOLTAGE_DIVIDER,
> + TEMP_SENSE_AMPLIFIER,
> };
>
> static const struct rescale_cfg rescale_cfg[] = {
> @@ -291,6 +310,10 @@ static const struct rescale_cfg rescale_cfg[] = {
> .type = IIO_VOLTAGE,
> .props = rescale_voltage_divider_props,
> },
> + [TEMP_SENSE_AMPLIFIER] = {
> + .type = IIO_TEMP,
> + .props = rescale_temp_sense_amplifier_props,
> + },
> };
>
> static const struct of_device_id rescale_match[] = {
> @@ -300,6 +323,8 @@ static const struct of_device_id rescale_match[] = {
> .data = &rescale_cfg[CURRENT_SENSE_SHUNT], },
> { .compatible = "voltage-divider",
> .data = &rescale_cfg[VOLTAGE_DIVIDER], },
> + { .compatible = "temperature-sense-amplifier",
> + .data = &rescale_cfg[TEMP_SENSE_AMPLIFIER], },
> { /* sentinel */ }
> };
> MODULE_DEVICE_TABLE(of, rescale_match);
>

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