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

On Sun, 2 Aug 2026 11:01:28 -0500
David Lechner <[email protected]> wrote:

> 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 <[email protected]>
> > Reviewed-by: Rodrigo Alencar <[email protected]>
> > ---
> >  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.

Good point.  I somehow keep forgetting we now have tests!

That can be a follow up patch

Jonathan

>