Re: [PATCH 1/3] iio: add IIO_VAL_DECIMAL64_{ATTO,ZEPTO,YOCTO} formats

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 22 Oct 2026 18:40:30 -0500
Victor Chernyakin <chernyakin.victor.j@outlook.com> wrote:

> The highest-precision format IIO has right now is IIO_VAL_DECIMAL64_FEMTO,
> which gives 15 decimal digits of precision after the decimal point. This
> is not enough for the upcoming TI FDC1004 driver, which needs 22 digits
> of precision to exactly express its scale value. This patch adds higher-
> precision formats, up to IIO_VAL_DECIMAL64_YOCTO (24 digits of precision).
> 
> Signed-off-by: Victor Chernyakin <chernyakin.victor.j@outlook.com>
Some discussion of whether these are perhaps overkill in the driver
patch given device precision doesn't seem to be nearly that good.
> ---
>  drivers/iio/industrialio-core.c | 6 ++++++
>  include/linux/iio/types.h       | 3 +++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 767a7794624a..008387efe96b 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -716,6 +716,9 @@ static ssize_t __iio_format_value(char *buf, size_t offset, unsigned int type,
>  	case IIO_VAL_DECIMAL64_NANO:
>  	case IIO_VAL_DECIMAL64_PICO:
>  	case IIO_VAL_DECIMAL64_FEMTO:

Seems we failed to update the test in drivers/iio/tests/iio-test-format.c for
FEMTO. Please add that and a similar test for your new units.

> +	case IIO_VAL_DECIMAL64_ATTO:
> +	case IIO_VAL_DECIMAL64_ZEPTO:
> +	case IIO_VAL_DECIMAL64_YOCTO:
>  	{
>  		int scale = type - IIO_VAL_DECIMAL64_BASE;
>  		s64 frac;
> @@ -1034,6 +1037,9 @@ static ssize_t iio_write_channel_info(struct device *dev,
>  		case IIO_VAL_DECIMAL64_NANO:
>  		case IIO_VAL_DECIMAL64_PICO:
>  		case IIO_VAL_DECIMAL64_FEMTO:
> +		case IIO_VAL_DECIMAL64_ATTO:
> +		case IIO_VAL_DECIMAL64_ZEPTO:
> +		case IIO_VAL_DECIMAL64_YOCTO:
>  			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 d8944c9e5e90..2ef9b2a8b119 100644
> --- a/include/linux/iio/types.h
> +++ b/include/linux/iio/types.h
> @@ -43,6 +43,9 @@ enum iio_event_info {
>  #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)
> +#define IIO_VAL_DECIMAL64_ATTO		(IIO_VAL_DECIMAL64_BASE + 18)
> +#define IIO_VAL_DECIMAL64_ZEPTO		(IIO_VAL_DECIMAL64_BASE + 21)
> +#define IIO_VAL_DECIMAL64_YOCTO		(IIO_VAL_DECIMAL64_BASE + 24)
>  
>  static inline s64 iio_val_s64_compose(s32 val0, s32 val1)
>  {