Re: [PATCH v3] iio: adc: ltc2471: Fix LTC2473 differential offset

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 10 Nov 2026 20:24:14 +0800
raoxu <raoxu@uniontech.com> wrote:

> From: Xu Rao <raoxu@uniontech.com>
> 
> The LTC2473 reports its differential conversion result as an unsigned
> 16-bit value spanning -VREF to +VREF. The IIO scale is consequently
> reported as 2 * VREF divided by 2^16.
> 
> IIO offsets are expressed in raw codes, but the driver currently returns
> -LTC2471_VREF, which is a millivolt value. This makes the processed
> reading incorrect: with a 1.25 V reference, the midpoint raw code is
> shifted by 1250 instead of 32768 codes.
> 
> Return the raw-code offset so that the midpoint maps to 0 mV and the
> endpoints map to -VREF and +VREF as intended. The single-ended LTC2471
> does not expose the offset attribute and is unaffected.
> 
> Fixes: 1d3eacbfa644 ("iio: Add LTC2471/LTC2473 driver")
> Cc: stable@vger.kernel.org
> Reviewed-by: Joshua Crofts <crofts@kernel.org>
> Reviewed-by: Nuno Sá <nuno.sa@analog.com>
> Signed-off-by: Xu Rao <raoxu@uniontech.com>
Applied to the fixes-togreg branch of iio.git

Thanks

Jonathan

> ---
> Changes in v3:
> - Add Reviewed-by tags from Nuno Sá and Joshua Crofts.
> - Move the AI assistance disclosure out of the commit message.
> - No code changes from v2.
> 
> Changes in v2:
> - Replace the raw -32768 literal with the named LTC2473_DIFF_OFFSET
>   macro.
> 
> The supplied fix was reviewed and this commit message prepared with
> OpenCode AI assistance.
> 
>  drivers/iio/adc/ltc2471.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/ltc2471.c b/drivers/iio/adc/ltc2471.c
> index 369af700969f..eb418c0fa732 100644
> --- a/drivers/iio/adc/ltc2471.c
> +++ b/drivers/iio/adc/ltc2471.c
> @@ -25,6 +25,7 @@ struct ltc2471_data {
> 
>  /* Reference voltage is 1.25V */
>  #define LTC2471_VREF 1250
> +#define LTC2473_DIFF_OFFSET (-32768)
> 
>  /* Read two bytes from the I2C bus to obtain the ADC result */
>  static int ltc2471_get_value(struct i2c_client *client)
> @@ -69,7 +70,7 @@ static int ltc2471_read_raw(struct iio_dev *indio_dev,
> 
>  	case IIO_CHAN_INFO_OFFSET:
>  		/* Only differential chip has this property */
> -		*val = -LTC2471_VREF;
> +		*val = LTC2473_DIFF_OFFSET;
>  		return IIO_VAL_INT;
> 
>  	default:
> --
> 2.50.1