Re: [PATCH v2 3/3] iio: flow: add Sensirion SLF3S liquid flow sensor driver

[Rodrigo Alencar]

On 26/05/28 12:22PM, Jonathan Cameron wrote:
> On Wed, 27 May 2026 20:42:54 +0200
> Wadim Mueller <wafgo01@xxxxxxxxx> wrote:
> 
> > Add a driver for the Sensirion SLF3S family of digital liquid-flow
> > sensors (SLF3S-0600F, SLF3S-1300F and SLF3S-4000B).  The sensors
> > communicate over I2C and return a 16-bit signed flow value, a 16-bit
> > signed temperature reading and a status word - each protected by a
> > CRC-8 byte - in every measurement frame.
> > 
> > The driver exposes:
> > 
> >   in_volumeflow_raw     - signed raw counts
> >   in_volumeflow_scale   - litres per second per LSB (per variant)
> >   in_temp_raw           - signed raw counts
> >   in_temp_scale         - millidegrees Celsius per LSB
> > 
> > The variant is auto-detected from the product-info word read at
> > probe time.  All three SLF3S devices are factory-calibrated for both
> > water and isopropyl alcohol; the calibration medium is selected via
> > the sensirion,medium device property and defaults to water.
> > 
> > Scale factors are taken from the respective datasheets (Table 16
> > for SLF3S-0600F, Table 15 for SLF3S-1300F and SLF3S-4000B):
> > 
> >   SLF3S-0600F:  10 (ul/min)^-1  -> 1/600 000 000 (l/s)/LSB
> >   SLF3S-1300F: 500 (ml/min)^-1  -> 1/30 000 000  (l/s)/LSB
> >   SLF3S-4000B:  32 (ml/min)^-1  -> 1/1 920 000   (l/s)/LSB

...

> > +static int slf3s_read_raw(struct iio_dev *indio_dev,
> > +			  struct iio_chan_spec const *chan, int *val,
> > +			  int *val2, long mask)
> > +{
> > +	struct slf3s_data *sf = iio_priv(indio_dev);
> > +	int flow, temp, ret;
> > +
> > +	switch (mask) {
> > +	case IIO_CHAN_INFO_RAW:
> > +		if (!iio_device_claim_direct(indio_dev))
> > +			return -EBUSY;
> > +
> > +		ret = slf3s_read_sample(sf, &flow, &temp);
> > +		iio_device_release_direct(indio_dev);
> > +		if (ret)
> > +			return ret;
> > +
> > +		*val = (chan->type == IIO_VOLUMEFLOW) ? flow : temp;
> > +		return IIO_VAL_INT;
> > +	case IIO_CHAN_INFO_SCALE:
> > +		if (chan->type == IIO_VOLUMEFLOW) {
> > +			*val = sf->variant->scale_num;
> > +			*val2 = sf->variant->scale_den;
> 
> Sashiko (probably correctly) identifies that the formatting that the IIO core
> does for an IIO_VAL_FRACTIONAL only goes to 9 decimal places.  That means
> in some cases the scale is truncated to 1 digit losing much of its usefulness.
> https://sashiko.dev/#/patchset/20260527184257.141635-1-wafgo01%40gmail.com
> 
> As such we need to increase the number of digits or maybe switch to using
> https://lore.kernel.org/all/20260524-adf41513-iio-driver-v14-6-06824d9c15f4@xxxxxxxxxx/
> 
> Which defines IIO_VAL_DECIMAL64_PICO

yes, pico would be enough, but IIO_VAL_DECIMAL64_FEMTO could also be defined if needed. 
There will be a v15, then let me know if any changes are needed.

-- 
Kind regards,

Rodrigo Alencar