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Date:   Sat, 30 Sep 2023 16:00:47 +0100
From:   Jonathan Cameron <jic23@kernel.org>
To:     David Lechner <dlechner@baylibre.com>
Cc:     linux-iio@vger.kernel.org, devicetree@vger.kernel.org,
        linux-staging@lists.linux.dev,
        David Lechner <david@lechnology.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Michael Hennerich <Michael.Hennerich@analog.com>,
        Nuno =?UTF-8?B?U8Oh?= <nuno.sa@analog.com>,
        Axel Haslam <ahaslam@baylibre.com>,
        Philip Molloy <pmolloy@baylibre.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 14/27] staging: iio: resolver: ad2s1210: implement
 hysteresis as channel attr
Message-ID: <20230930160047.0c5a5388@jic23-huawei>
In-Reply-To: <CAMknhBGFBwQQouhsPMgCuMn6+eQfDCcSzJvF-DwJAnoEPvMLAA@mail.gmail.com>
References: <20230929-ad2s1210-mainline-v3-0-fa4364281745@baylibre.com>
        <20230929-ad2s1210-mainline-v3-14-fa4364281745@baylibre.com>
        <CAMknhBGFBwQQouhsPMgCuMn6+eQfDCcSzJvF-DwJAnoEPvMLAA@mail.gmail.com>
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On Fri, 29 Sep 2023 12:53:00 -0500
David Lechner <dlechner@baylibre.com> wrote:

> On Fri, Sep 29, 2023 at 12:25=E2=80=AFPM David Lechner <dlechner@baylibre=
.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@baylibre.com>
> > --- =20
>=20
> ...
>=20
> > +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[] =3D { 0, 1 }; =20
>=20
> 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


>=20
> > +
> > +       switch (mask) {
> > +       case IIO_CHAN_INFO_HYSTERESIS:
> > +               switch (chan->type) {
> > +               case IIO_ANGL:
> > +                       *vals =3D hysteresis_available;
> > +                       *type =3D IIO_VAL_INT;
> > +                       *length =3D ARRAY_SIZE(hysteresis_available);
> > +                       return IIO_AVAIL_LIST;
> > +               default:
> > +                       return -EINVAL;
> > +               }
> > +       default:
> > +               return -EINVAL;
> > +       }
> > +}
> > =20