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

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

[raoxu]

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.

The supplied fix was reviewed and this commit message prepared with
OpenCode AI assistance.

Fixes: 1d3eacbfa644 ("iio: Add LTC2471/LTC2473 driver")
Signed-off-by: Xu Rao <raoxu@uniontech.com>
Cc: stable@vger.kernel.org
---
 drivers/iio/adc/ltc2471.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iio/adc/ltc2471.c b/drivers/iio/adc/ltc2471.c
index 369af700969f..1c88c824d92d 100644
--- a/drivers/iio/adc/ltc2471.c
+++ b/drivers/iio/adc/ltc2471.c
@@ -69,7 +69,7 @@ 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 = -32768;
 		return IIO_VAL_INT;

 	default:
--
2.50.1

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

[Nuno Sá]

On Mon, Nov 09, 2026 at 05:55:53PM +0800, raoxu 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.
> 
> The supplied fix was reviewed and this commit message prepared with
> OpenCode AI assistance.
> 
> Fixes: 1d3eacbfa644 ("iio: Add LTC2471/LTC2473 driver")
> Signed-off-by: Xu Rao <raoxu@uniontech.com>
> Cc: stable@vger.kernel.org
> ---

Auch! LGTM

Reviewed-by: Nuno Sá <nuno.sa@analog.com>

>  drivers/iio/adc/ltc2471.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/ltc2471.c b/drivers/iio/adc/ltc2471.c
> index 369af700969f..1c88c824d92d 100644
> --- a/drivers/iio/adc/ltc2471.c
> +++ b/drivers/iio/adc/ltc2471.c
> @@ -69,7 +69,7 @@ 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 = -32768;
>  		return IIO_VAL_INT;
> 
>  	default:
> --
> 2.50.1
>