On Thu, 19 Oct 2023 16:23:56 +0300
Matti Vaittinen <mazziesaccount@xxxxxxxxx> 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@xxxxxxxxx>
> Reported-by: Jagath Jog J <jagathjog1996@xxxxxxxxx>
> 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.
MEMS accelerometers tend to be pretty inaccurate. So I'd not worry too much about
this loss of accuracy at all.
The 0 point according to the datasheet I just looked at is +- 25mg and
if I read the sensitivity numbers right part to part variation in scale
is well above 5%. For 2G mode, it lists acceptable 1G values of
min=15401, typical=16384, max=17367
So if anyone actually wants to do precision measurement they need to calibrate
their particular device + deal with the variation due to temperature etc
which makes this even more fun.
Applied to my local fixes-togreg branch of iio.git, but I've just sent a pull request
so this may not go out until after the 6.7 merge window.
Jonathan
>
> 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 :)
>
> ---
> 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,
