Re: [PATCH RFC] iio: adc: ad4030: fix calibscale read/write unit mismatch

[Nuno Sá]

On Wed, 2026-02-25 at 09:20 -0600, David Lechner wrote:
> On 2/25/26 5:53 AM, Marcelo Schmitt wrote:
> > On 02/25, Giorgi Tchankvetadze wrote:
> > > The read path returns calibscale in IIO_VAL_INT_PLUS_NANO but the write
> > > path treats it as MICRO. Since no write_raw_get_fmt is provided, the
> > > IIO core defaults to MICRO when parsing userspace input.
> > > 
> > > This means reading calibscale and writing it back results in a ~1000x
> > > gain error.
> > > 
> > > Change the read path and available range to use MICRO to match the
> > > write path.
> > 
> > The updates to ad4030 driver will add write_raw_get_fmt() [1].
> > [1]:
> > https://lore.kernel.org/linux-iio/516cccc47e917bd26be29b016907f50a244a68b9.1771865684.git.marcelo.schmitt@xxxxxxxxxx/
> > 
> > At first glance, I think this could instead add a case to write_raw_get_fmt(),
> > keeping calibscale nano precision (unless nano precision doesn't make sense
> > for ad4030 calibscale (don't recall from top of my mind)).
> 
> Since this is a fix and needs to be backported, it probably make sense
> to not depend on a patch that is adding new features.
> 

+1

- Nuno Sá

> I'm sure Jonathan will have an opinion about how he would like to handle
> a conflict between the fixes and testing branches though.
> 
> > 
> > > 
> > > Fixes: 0cb8b324852f ("iio: adc: ad4030: add driver for ad4030-24")
> > > Signed-off-by: Giorgi Tchankvetadze <giorgitchankvetadze1997@xxxxxxxxx>
> > > ---
> > >  drivers/iio/adc/ad4030.c | 10 +++++-----
> > >  1 file changed, 5 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/iio/adc/ad4030.c b/drivers/iio/adc/ad4030.c
> > > index def3e1d01ceb..3d823648371d 100644
> > > --- a/drivers/iio/adc/ad4030.c
> > > +++ b/drivers/iio/adc/ad4030.c
> > > @@ -423,10 +423,10 @@ static int ad4030_get_chan_calibscale(struct iio_dev *indio_dev,
> > >  
> > >  	/* From datasheet: multiplied output = input × gain word/0x8000 */
> > >  	*val = gain / AD4030_GAIN_MIDLE_POINT;
> > > -	*val2 = mul_u64_u32_div(gain % AD4030_GAIN_MIDLE_POINT, NANO,
> > > +	*val2 = mul_u64_u32_div(gain % AD4030_GAIN_MIDLE_POINT, MICRO,
> > >  				AD4030_GAIN_MIDLE_POINT);
> > >  
> > > -	return IIO_VAL_INT_PLUS_NANO;
> > > +	return IIO_VAL_INT_PLUS_MICRO;
> > >  }
> > >  
> > >  /* Returns the offset where 1 LSB = (VREF/2^precision_bits - 1)/gain */
> > > @@ -720,8 +720,8 @@ static irqreturn_t ad4030_trigger_handler(int irq, void *p)
> > >  
> > >  static const int ad4030_gain_avail[3][2] = {
> > >  	{ 0, 0 },
> > > -	{ 0, 30518 },
> > > -	{ 1, 999969482 },
> > > +	{ 0, 30 },
> > > +	{ 1, 999969 },
> 
> This loses precision. Instead I would change the write to IIO_VAL_INT_PLUS_NANO
> to match the read.
> 
> > >  };
> > >  
> > >  static int ad4030_read_avail(struct iio_dev *indio_dev,
> > > @@ -739,7 +739,7 @@ static int ad4030_read_avail(struct iio_dev *indio_dev,
> > >  
> > >  	case IIO_CHAN_INFO_CALIBSCALE:
> > >  		*vals = (void *)ad4030_gain_avail;
> > > -		*type = IIO_VAL_INT_PLUS_NANO;
> > > +		*type = IIO_VAL_INT_PLUS_MICRO;
> > >  		return IIO_AVAIL_RANGE;
> > >  
> > >  	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> > > -- 
> > > 2.52.0
> > > 
> > >