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

[Giorgi Tchankvetadze]

Hi Marcelo, Thanks for the pointer to your pending series. As for
keeping NANO precision, the hardware register is 16-bit with a step of
1/0x8000 ≈ 30 µ, so NANO doesn't provide any additional precision that
the hardware can actually represent. MICRO is sufficient.

Btw, I checked and found that no driver in the entire IIO tree uses
NANO for calibscale.
Drivers use either IIO_VAL_INT (raw register value) or IIO_VAL_INT_PLUS_MICRO.

That said, if your series is already adding write_raw_get_fmt(), I'm
happy to drop this patch and let yours handle it - as long as the
mismatch gets fixed either way.

Regards, Giorgi

On Wed, Feb 25, 2026 at 3:53 PM Marcelo Schmitt
<marcelo.schmitt1@xxxxxxxxx> 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)).
>
> >
> > 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 в 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 },
> >  };
> >
> >  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
> >
> >