Re: [PATCH v6 3/4] iio: core: add IIO_VAL_DECIMAL64_FEMTO format type

[David Lechner <dlechner@baylibre.com>]

On 7/28/26 4:49 PM, Wadim Mueller wrote:
> Extend the IIO_VAL_DECIMAL64_* family with a femto-scaled variant
> (scale 15), following the existing MILLI/MICRO/NANO/PICO pattern. Both
> the read formatting path in __iio_format_value() and the write parsing
> path in iio_write_channel_info() (via kstrtodec64()) already derive
> their scale from "type - IIO_VAL_DECIMAL64_BASE", so the new type only
> needs to be added to the respective switch cases.
> 
> This is needed by drivers reporting very small SI quantities where the
> existing pico scale loses precision. For example the Sensirion SLF3S
> liquid flow sensor reports its volume-flow scale in m^3/s, where the
> SLF3S-0600F scale is ~1.667e-12 m^3/s: at pico scale only a single
> significant digit survives, whereas femto scale preserves the full
> sensor resolution.
> 
> Signed-off-by: Wadim Mueller <wafgo01@gmail.com>
> Reviewed-by: Rodrigo Alencar <rodrigo.alencar@analog.com>
> ---
>  drivers/iio/industrialio-core.c | 2 ++
>  include/linux/iio/types.h       | 1 +
>  2 files changed, 3 insertions(+)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 37cf2817b3d0..767a7794624a 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -715,6 +715,7 @@ static ssize_t __iio_format_value(char *buf, size_t offset, unsigned int type,
>  	case IIO_VAL_DECIMAL64_MICRO:
>  	case IIO_VAL_DECIMAL64_NANO:
>  	case IIO_VAL_DECIMAL64_PICO:
> +	case IIO_VAL_DECIMAL64_FEMTO:
>  	{
>  		int scale = type - IIO_VAL_DECIMAL64_BASE;
>  		s64 frac;
> @@ -1032,6 +1033,7 @@ static ssize_t iio_write_channel_info(struct device *dev,
>  		case IIO_VAL_DECIMAL64_MICRO:
>  		case IIO_VAL_DECIMAL64_NANO:
>  		case IIO_VAL_DECIMAL64_PICO:
> +		case IIO_VAL_DECIMAL64_FEMTO:
>  			dec_scale = type - IIO_VAL_DECIMAL64_BASE;
>  			fallthrough;
>  		case IIO_VAL_INT_64:
> diff --git a/include/linux/iio/types.h b/include/linux/iio/types.h
> index 924ac9dc6893..d8944c9e5e90 100644
> --- a/include/linux/iio/types.h
> +++ b/include/linux/iio/types.h
> @@ -42,6 +42,7 @@ enum iio_event_info {
>  #define IIO_VAL_DECIMAL64_MICRO		(IIO_VAL_DECIMAL64_BASE + 6)
>  #define IIO_VAL_DECIMAL64_NANO		(IIO_VAL_DECIMAL64_BASE + 9)
>  #define IIO_VAL_DECIMAL64_PICO		(IIO_VAL_DECIMAL64_BASE + 12)
> +#define IIO_VAL_DECIMAL64_FEMTO		(IIO_VAL_DECIMAL64_BASE + 15)
>  
>  static inline s64 iio_val_s64_compose(s32 val0, s32 val1)
>  {

Would be nice to add this to drivers/iio/test/iio-test-format.c too.