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

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Message-ID: <CAMknhBHdcLNxX8mzTyjSBeoDdXjyT_8LebtzCthBPHeFwYyjsA@mail.gmail.com>
Date:   Sat, 30 Sep 2023 16:23:19 -0500
From:   David Lechner <dlechner@...libre.com>
To:     Jonathan Cameron <jic23@...nel.org>
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 Sat, Sep 30, 2023 at 10:00 AM Jonathan Cameron <jic23@...nel.org> wrote:
>
> 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?
>

It is currently only correct (as a raw value) if the selected
resolution is 16-bit. So I will need to fix this so the value is `1 <<
(16 - resolution)`.