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References: <20240216-ad7944-mainline-v2-0-7eb69651e592@baylibre.com> <20240216-ad7944-mainline-v2-2-7eb69651e592@baylibre.com>
In-Reply-To: <20240216-ad7944-mainline-v2-2-7eb69651e592@baylibre.com>
From: David Lechner <dlechner@baylibre.com>
Date: Mon, 19 Feb 2024 13:13:35 -0600
Message-ID: <CAMknhBH2Pqa9xpPxnTCxJegVTbOG-QDeJA4YrQUPfj+hfSs73A@mail.gmail.com>
Subject: Re: [PATCH v2 2/2] iio: adc: ad7944: add driver for AD7944/AD7985/AD7986
To: linux-iio@vger.kernel.org
Cc: Michael Hennerich <Michael.Hennerich@analog.com>, Jonathan Cameron <jic23@kernel.org>, 
	Rob Herring <robh+dt@kernel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>, Conor Dooley <conor+dt@kernel.org>, 
	=?UTF-8?B?TnVubyBTw6E=?= <nuno.sa@analog.com>, 
	Liam Girdwood <lgirdwood@gmail.com>, Mark Brown <broonie@kernel.org>, devicetree@vger.kernel.org, 
	linux-kernel@vger.kernel.org
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On Fri, Feb 16, 2024 at 1:47=E2=80=AFPM David Lechner <dlechner@baylibre.co=
m> wrote:

..

> +
> +#define AD7944_DEFINE_CHIP_INFO(_name, _t, _bits, _sign)               \
> +static const struct ad7944_chip_info _name##_chip_info =3D {            =
 \
> +       .name =3D #_name,                                                =
 \
> +       .t =3D &_t##_timing_spec,                                        =
 \
> +       .channels =3D {                                                  =
 \
> +               {                                                       \
> +                       .type =3D IIO_VOLTAGE,                           =
 \
> +                       .indexed =3D 1,                                  =
 \
> +                       .differential =3D 1,                             =
 \
> +                       .channel =3D 0,                                  =
 \
> +                       .channel2 =3D 1,                                 =
 \
> +                       .scan_index =3D 0,                               =
 \
> +                       .scan_type.sign =3D _sign,                       =
 \
> +                       .scan_type.realbits =3D _bits,                   =
 \
> +                       .scan_type.storagebits =3D _bits > 16 ? 32 : 16, =
 \
> +                       .scan_type.endianness =3D IIO_CPU,               =
 \
> +                       .info_mask_separate =3D BIT(IIO_CHAN_INFO_RAW)   =
 \
> +                                       | BIT(IIO_CHAN_INFO_SCALE),     \
> +               },                                                      \
> +               IIO_CHAN_SOFT_TIMESTAMP(1),                             \
> +       },                                                              \
> +}
> +
> +AD7944_DEFINE_CHIP_INFO(ad7944, ad7944, 14, 'u');
> +AD7944_DEFINE_CHIP_INFO(ad7985, ad7944, 16, 'u');
> +AD7944_DEFINE_CHIP_INFO(ad7986, ad7986, 18, 's');

Now that I have been enlightened [1] about pseudo-differntial inputs,
I'm thinking that AD7944 and AD7985 should not have the .differential
=3D 1 flag set since they are pseudo-differential inputs with a ground
sense on the negative input (and no extra supply needed since it is
always ground). Does that sound right?

AD7986 is true differential though, so should be correct already.

[1]: https://lore.kernel.org/linux-iio/CAMknhBF5mAsN1c-194Qwa5oKmqKzef2khXn=
qA1cSdKpWHKWp0w@mail.gmail.com/