linux-kernel - Re: [PATCH v2 2/2] iio: adc: ad7944: add driver for AD7944/AD7985/AD7986

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Date: Mon, 19 Feb 2024 13:13:35 -0600
From: David Lechner <dlechner@...libre.com>
To: linux-iio@...r.kernel.org
Cc: Michael Hennerich <Michael.Hennerich@...log.com>, Jonathan Cameron <jic23@...nel.org>, 
	Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Nuno Sá <nuno.sa@...log.com>, 
	Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] iio: adc: ad7944: add driver for AD7944/AD7985/AD7986

On Fri, Feb 16, 2024 at 1:47 PM David Lechner <dlechner@...libre.com> wrote:

..

> +
> +#define AD7944_DEFINE_CHIP_INFO(_name, _t, _bits, _sign)               \
> +static const struct ad7944_chip_info _name##_chip_info = {             \
> +       .name = #_name,                                                 \
> +       .t = &_t##_timing_spec,                                         \
> +       .channels = {                                                   \
> +               {                                                       \
> +                       .type = IIO_VOLTAGE,                            \
> +                       .indexed = 1,                                   \
> +                       .differential = 1,                              \
> +                       .channel = 0,                                   \
> +                       .channel2 = 1,                                  \
> +                       .scan_index = 0,                                \
> +                       .scan_type.sign = _sign,                        \
> +                       .scan_type.realbits = _bits,                    \
> +                       .scan_type.storagebits = _bits > 16 ? 32 : 16,  \
> +                       .scan_type.endianness = IIO_CPU,                \
> +                       .info_mask_separate = 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
= 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-194Qwa5oKmqKzef2khXnqA1cSdKpWHKWp0w@mail.gmail.com/