Re: [PATCH] iio: kx022a: Fix acceleration value scaling

[Matti Vaittinen]

On 10/19/23 21:21, Jagath Jog J wrote:
> Hi Matti,
>
> On Thu, Oct 19, 2023 at 6:54 PM 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.
> >
> > 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@xxxxxxxxx>

Thanks a ton for testing! May I ask which component did you use (or did 
you just use some 'simulated' regster values?)

Yours,
	-- Matti

--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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