Re: [lm-sensors] [PATCH v3] hwmon: ntc: fix iio raw to microvolts conversion

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

On 06/01/2015 09:27 AM, Chris Lesiak wrote:
> The function ntc_adc_iio_read was assuming both a 12 bit ADC and that
> pullup_uv is the same as the ADC reference voltage.  If either
> assumption is false, then the result is incorrect.
>
> Attempt to use iio_convert_raw_to_processed to convert the raw value to
> microvolts.  It will fail for iio channels that don't support support

But we need millivolts ?

Guenter

> IIO_CHAN_INFO_SCALE; in that case fall back to the assumptions.
>
> Signed-off-by: Chris Lesiak <chris.lesiak@licor.com>
> ---
>   drivers/hwmon/ntc_thermistor.c | 15 ++++++++-------
>   1 file changed, 8 insertions(+), 7 deletions(-)
>
> This patch was previously titled:
> "hwmon: ntc: use iio_read_channel_processed if possible"
> but that doesn't describe it anymore.
>
> Changes in v3
> ======>
> - Don't use iio_read_channel_processed because it does not return results in
>    microvolts.
>
> - Do use iio_convert_raw_to_processed with a scale factor of 1000 to get
>    microvolts instead of the iio normal unit of millivolts.
>
> - Do it all in the context of the original ntc_adc_iio_read function instead
>    of having separate read functions for the raw and processed cases.
>
> diff --git a/drivers/hwmon/ntc_thermistor.c b/drivers/hwmon/ntc_thermistor.c
> index 6880011..e08ed47 100644
> --- a/drivers/hwmon/ntc_thermistor.c
> +++ b/drivers/hwmon/ntc_thermistor.c
> @@ -190,20 +190,21 @@ struct ntc_data {
>   static int ntc_adc_iio_read(struct ntc_thermistor_platform_data *pdata)
>   {
>   	struct iio_channel *channel = pdata->chan;
> -	s64 result;
> -	int val, ret;
> +	int raw, uv, ret;
>
> -	ret = iio_read_channel_raw(channel, &val);
> +	ret = iio_read_channel_raw(channel, &raw);
>   	if (ret < 0) {
>   		pr_err("read channel() error: %d\n", ret);
>   		return ret;
>   	}
>
> -	/* unit: mV */
> -	result = pdata->pullup_uv * (s64) val;
> -	result >>= 12;
> +	ret = iio_convert_raw_to_processed(channel, raw, &uv, 1000);
> +	if (ret < 0) {
> +		/* Assume 12 bit ADC with vref at pullup_uv*/
> +		uv = (pdata->pullup_uv * (s64)raw) >> 12;
> +	}
>
> -	return (int)result;
> +	return uv;
>   }
>
>   static const struct of_device_id ntc_match[] = {
>


_______________________________________________
lm-sensors mailing list
lm-sensors@lm-sensors.org
http://lists.lm-sensors.org/mailman/listinfo/lm-sensors