On 01/07, Jonathan Santos wrote:
> From: Sergiu Cuciurean <sergiu.cuciurean@xxxxxxxxxx>
>
> The ad7768-1 is a fully differential ADC, meaning that the voltage
> conversion result is a signed value. Since the value is a 24 bit one,
Hmm, I think the reason why we sign _raw values should be because of the ADC
output code format. There are differential ADCs that can measure a negative
difference between IN+ and IN- but outputting straight binary data format (not
signed values). In those cases, the _offset attribute is used to "shift" the
_raw value so that output codes that represent IN+ < IN- are adjusted to a
negative decimal value (the _raw + _offset part of IIO ABI to get to mV units).
For AD7768-1/ADAQ7768-1, the ADC output code is indeed two's complement and thus
signed so the code change is correct for it.
Since you are probably going to re-spin on the patch series, will be nice
to adjust the message to something like:
The ad7768-1 ADC output code is two's complement, meaning that the voltage
conversion result is a signed value. ...
With that,
Reviewed-by: Marcelo Schmitt <marcelo.schmitt@xxxxxxxxxx>
> stored in a 32 bit variable, the sign should be extended in order to get
> the correct representation.
>
> Also the channel description has been updated to signed representation,
> to match the ADC specifications.
>
> Fixes: a5f8c7da3dbe ("iio: adc: Add AD7768-1 ADC basic support")
> Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@xxxxxxxxxx>
> ---
> drivers/iio/adc/ad7768-1.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
> index 113703fb7245..c3cf04311c40 100644
> --- a/drivers/iio/adc/ad7768-1.c
> +++ b/drivers/iio/adc/ad7768-1.c
> @@ -142,7 +142,7 @@ static const struct iio_chan_spec ad7768_channels[] = {
> .channel = 0,
> .scan_index = 0,
> .scan_type = {
> - .sign = 'u',
> + .sign = 's',
> .realbits = 24,
> .storagebits = 32,
> .shift = 8,
> @@ -371,7 +371,7 @@ static int ad7768_read_raw(struct iio_dev *indio_dev,
>
> ret = ad7768_scan_direct(indio_dev);
> if (ret >= 0)
> - *val = ret;
> + *val = sign_extend32(ret, chan->scan_type.realbits - 1);
>
> iio_device_release_direct_mode(indio_dev);
> if (ret < 0)
> --
> 2.34.1
>
