linux-kernel - Re: [PATCH] iio: kx022a: Fix acceleration value scaling

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Message-ID: <CAM+2Eu+ndzS9NLvsZaX_=YTHb_+t4cE5GjQevJ1Lgc2EBO20rA@mail.gmail.com>
Date:   Thu, 19 Oct 2023 23:51:27 +0530
From:   Jagath Jog J <jagathjog1996@...il.com>
To:     Matti Vaittinen <mazziesaccount@...il.com>
Cc:     Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Mehdi Djait <mehdi.djait.k@...il.com>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: kx022a: Fix acceleration value scaling

Hi Matti,

On Thu, Oct 19, 2023 at 6:54 PM Matti Vaittinen
<mazziesaccount@...il.com> wrote:
>
> The IIO ABI mandates acceleration values from accelerometer to be
> emitted in m/s^2. The KX022A was emitting values in micro m/s^2.
>
> Fix driver to report the correct scale values.
>
> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
> Reported-by: Jagath Jog J <jagathjog1996@...il.com>
> Fixes: 7c1d1677b322 ("iio: accel: Support Kionix/ROHM KX022A accelerometer")
>
> ---
> The fix is somewhat crude and just crops the last 3 digits (rounds) of the
> scale while using IIO_VAL_INT_PLUS_NANO. I played with a thought of using
> IIO_VAL_FRACTIONAL, which could have modelled the computation
> G_range * g * scaling / (2^16 * scaling) - where scaling 10000 would
> have allowed using g value 980665.
>
> This would have worked fine for reporting scale and available scales -
> but would be somewhat tricky when converting the user-supplied scale to
> register values in write_raw().
>
> Well, the g varies from 9.832 (poles) to 9.780 (equator) according to
> some website - no proper source check done but this sounds about right -
> so maybe the loss of accuracy is acceptable.
>
> I did only very quick testing on KX022A and iio_generic_buffer. After
> the patch the values seemed to be correct order of magnitude. Further
> testing is appreciated :)

Values are correct with this change, Thank you for fixing.
Tested-by: Jagath Jog J <jagathjog1996@...il.com>

Regards
Jagath


>
> ---
>  drivers/iio/accel/kionix-kx022a.c | 37 ++++++++++++++++++++++---------
>  1 file changed, 26 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/iio/accel/kionix-kx022a.c b/drivers/iio/accel/kionix-kx022a.c
> index 4ea3c6718ed4..971fc60efef0 100644
> --- a/drivers/iio/accel/kionix-kx022a.c
> +++ b/drivers/iio/accel/kionix-kx022a.c
> @@ -273,17 +273,17 @@ static const unsigned int kx022a_odrs[] = {
>   *     (range / 2^bits) * g = (range / 2^bits) * 9.80665 m/s^2
>   *     => KX022A uses 16 bit (HiRes mode - assume the low 8 bits are zeroed
>   *     in low-power mode(?) )
> - *     => +/-2G  => 4 / 2^16 * 9,80665 * 10^6 (to scale to micro)
> - *     => +/-2G  - 598.550415
> - *        +/-4G  - 1197.10083
> - *        +/-8G  - 2394.20166
> - *        +/-16G - 4788.40332
> + *     => +/-2G  => 4 / 2^16 * 9,80665
> + *     => +/-2G  - 0.000598550415
> + *        +/-4G  - 0.00119710083
> + *        +/-8G  - 0.00239420166
> + *        +/-16G - 0.00478840332
>   */
>  static const int kx022a_scale_table[][2] = {
> -       { 598, 550415 },
> -       { 1197, 100830 },
> -       { 2394, 201660 },
> -       { 4788, 403320 },
> +       { 0, 598550 },
> +       { 0, 1197101 },
> +       { 0, 2394202 },
> +       { 0, 4788403 },
>  };
>
>  static int kx022a_read_avail(struct iio_dev *indio_dev,
> @@ -302,7 +302,7 @@ static int kx022a_read_avail(struct iio_dev *indio_dev,
>                 *vals = (const int *)kx022a_scale_table;
>                 *length = ARRAY_SIZE(kx022a_scale_table) *
>                           ARRAY_SIZE(kx022a_scale_table[0]);
> -               *type = IIO_VAL_INT_PLUS_MICRO;
> +               *type = IIO_VAL_INT_PLUS_NANO;
>                 return IIO_AVAIL_LIST;
>         default:
>                 return -EINVAL;
> @@ -366,6 +366,20 @@ static int kx022a_turn_on_unlock(struct kx022a_data *data)
>         return ret;
>  }
>
> +static int kx022a_write_raw_get_fmt(struct iio_dev *idev,
> +                                   struct iio_chan_spec const *chan,
> +                                   long mask)
> +{
> +       switch (mask) {
> +       case IIO_CHAN_INFO_SCALE:
> +               return IIO_VAL_INT_PLUS_NANO;
> +       case IIO_CHAN_INFO_SAMP_FREQ:
> +               return IIO_VAL_INT_PLUS_MICRO;
> +       default:
> +               return -EINVAL;
> +       }
> +}
> +
>  static int kx022a_write_raw(struct iio_dev *idev,
>                             struct iio_chan_spec const *chan,
>                             int val, int val2, long mask)
> @@ -510,7 +524,7 @@ static int kx022a_read_raw(struct iio_dev *idev,
>
>                 kx022a_reg2scale(regval, val, val2);
>
> -               return IIO_VAL_INT_PLUS_MICRO;
> +               return IIO_VAL_INT_PLUS_NANO;
>         }
>
>         return -EINVAL;
> @@ -712,6 +726,7 @@ static int kx022a_fifo_flush(struct iio_dev *idev, unsigned int samples)
>  static const struct iio_info kx022a_info = {
>         .read_raw = &kx022a_read_raw,
>         .write_raw = &kx022a_write_raw,
> +       .write_raw_get_fmt = &kx022a_write_raw_get_fmt,
>         .read_avail = &kx022a_read_avail,
>
>         .validate_trigger       = iio_validate_own_trigger,
> --
> 2.41.0
>
>
> --
> Matti Vaittinen, Linux device drivers
> ROHM Semiconductors, Finland SWDC
> Kiviharjunlenkki 1E
> 90220 OULU
> FINLAND
>
> ~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
> Simon says - in Latin please.
> ~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
> Thanks to Simon Glass for the translation =]