linux-kernel - Re: [PATCH] iio: adis16201: Correct accelerometer scale factor

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Message-ID: <CAKUZ0z+cd6VREDjiqMVy5k8rpV=NC+-YGQvBFYwYfFZ8iQbL1w@mail.gmail.com>
Date: Sat, 19 Apr 2025 20:57:06 -0400
From: Gabriel Shahrouzi <gshahrouzi@...il.com>
To: Marcelo Schmitt <marcelo.schmitt1@...il.com>
Cc: himanshujha199640@...il.com, jic23@...nel.org, lars@...afoo.de, 
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Michael.Hennerich@...log.com, skhan@...uxfoundation.org, 
	linux-kernel-mentees@...ts.linux.dev, stable@...r.kernel.org
Subject: Re: [PATCH] iio: adis16201: Correct accelerometer scale factor

On Sat, Apr 19, 2025 at 2:13 PM Marcelo Schmitt
<marcelo.schmitt1@...il.com> wrote:
>
> LGTM. Minor comments inline.
>
> On 04/19, Gabriel Shahrouzi wrote:
> > The IIO_CHAN_INFO_SCALE previously reported for accelerometer channels
> > used 0.4624 mg/LSB. This value matches the datasheet specification for
> > the offset calibration registers (X/YACCL_OFFS_REG, pg 18).
> >
> > However, the scale should reflect the sensor output data registers
> > (X/YACCL_OUT, pg 15, Tables 7 & 8), which use 0.4625 mg/LSB. This is
> > also consistent with the typical sensitivity in Table 1 (1 / 2.162 ≈
> > 0.4625).
> >
> > Fixes: 57f9386405a2 ("Staging: iio: accel: adis16201: Add comments about units in read_raw()")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Gabriel Shahrouzi <gshahrouzi@...il.com>
> > ---
>
> >  drivers/iio/accel/adis16201.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/iio/accel/adis16201.c b/drivers/iio/accel/adis16201.c
> > index 8601b9a8b8e75..982b33f6eccac 100644
> > --- a/drivers/iio/accel/adis16201.c
> > +++ b/drivers/iio/accel/adis16201.c
> > @@ -133,7 +133,7 @@ static int adis16201_read_raw(struct iio_dev *indio_dev,
> >                        * 1 LSB represents 0.244 mg.
> Maybe also update the comment?
Good catch. I will update that for v2.
>
> >                        */
> >                       *val = 0;
> > -                     *val2 = IIO_G_TO_M_S_2(462400);
> > +                     *val2 = IIO_G_TO_M_S_2(462500);
> If we do the math with more decimal digitis we have 1 / 2.162 == 0.46253469010176
> Would it make sense to do
>                         *val2 = IIO_G_TO_M_S_2(462535);
> ?
Since the datasheet lists the scale factor as 0.4625 mg, I believe
using *val2 = IIO_G_TO_M_S_2(462500); is correct. However, I'm not
sure so I'll postpone v2.
>
> >                       return IIO_VAL_INT_PLUS_NANO;
> >               case IIO_INCLI:
> >                       *val = 0;