linux-kernel - Re: [PATCH v3 14/27] staging: iio: resolver: ad2s1210: implement hysteresis as channel attr

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Date:   Sat, 30 Sep 2023 16:00:47 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     David Lechner <dlechner@...libre.com>
Cc:     linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-staging@...ts.linux.dev,
        David Lechner <david@...hnology.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Nuno Sá <nuno.sa@...log.com>,
        Axel Haslam <ahaslam@...libre.com>,
        Philip Molloy <pmolloy@...libre.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 14/27] staging: iio: resolver: ad2s1210: implement
 hysteresis as channel attr

On Fri, 29 Sep 2023 12:53:00 -0500
David Lechner <dlechner@...libre.com> wrote:

> On Fri, Sep 29, 2023 at 12:25 PM David Lechner <dlechner@...libre.com> wrote:
> >
> > The AD2S1210 resolver has a hysteresis feature that can be used to
> > prevent flicker in the LSB of the position register. This can be either
> > enabled or disabled. Disabling hysteresis is useful for increasing
> > precision by oversampling.
> >
> > Signed-off-by: David Lechner <dlechner@...libre.com>
> > ---  
> 
> ...
> 
> > +static int ad2s1210_read_avail(struct iio_dev *indio_dev,
> > +                              struct iio_chan_spec const *chan,
> > +                              const int **vals, int *type,
> > +                              int *length, long mask)
> > +{
> > +       static const int hysteresis_available[] = { 0, 1 };  
> 
> This is basically an enable/disable. Should the 1 value be changed to the
> appropriate radians value since this is hysteresis on the position
> (angle) channel?

Good point. However it should be in the _raw units. The text is
slightly more explicit on this for
the variant of hysteresis applied to threshold events as it's
added or substracted from a threshold (and thresholds are in
_raw readings unless only _processed is available).

Does that make 0, 1 correct as we are talking about LSB only?

Jonathan


> 
> > +
> > +       switch (mask) {
> > +       case IIO_CHAN_INFO_HYSTERESIS:
> > +               switch (chan->type) {
> > +               case IIO_ANGL:
> > +                       *vals = hysteresis_available;
> > +                       *type = IIO_VAL_INT;
> > +                       *length = ARRAY_SIZE(hysteresis_available);
> > +                       return IIO_AVAIL_LIST;
> > +               default:
> > +                       return -EINVAL;
> > +               }
> > +       default:
> > +               return -EINVAL;
> > +       }
> > +}
> >