linux-kernel - Re: [PATCH 6/6] iio: adc: ad7173: Add support for AD411x devices

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Message-ID: <CAMknhBH-YmFrqNTQCB_KafCTxEqSL+36pkE0O44NqiL89hm64Q@mail.gmail.com>
Date: Mon, 1 Apr 2024 16:53:26 -0500
From: David Lechner <dlechner@...libre.com>
To: dumitru.ceclan@...log.com
Cc: Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich <Michael.Hennerich@...log.com>, 
	Jonathan Cameron <jic23@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Dumitru Ceclan <mitrutzceclan@...il.com>
Subject: Re: [PATCH 6/6] iio: adc: ad7173: Add support for AD411x devices

On Mon, Apr 1, 2024 at 10:10 AM Dumitru Ceclan via B4 Relay
<devnull+dumitru.ceclan.analog.com@...nel.org> wrote:
>
> From: Dumitru Ceclan <dumitru.ceclan@...log.com>
>
> Add support for AD4111/AD4112/AD4114/AD4115/AD4116.
>
> The AD411X family encompasses a series of low power, low noise, 24-bit,
> sigma-delta analog-to-digital converters that offer a versatile range of
> specifications.
>
> This family of ADCs integrates an analog front end suitable for processing
> both fully differential and single-ended, bipolar voltage inputs
> addressing a wide array of industrial and instrumentation requirements.
>
> - All ADCs have inputs with a precision voltage divider with a division
>   ratio of 10.
> - AD4116 has 5 low level inputs without a voltage divider.
> - AD4111 and AD4112 support current inputs (0 mA to 20 mA) using a 50ohm
>   shunt resistor.
>
> Signed-off-by: Dumitru Ceclan <dumitru.ceclan@...log.com>
> ---

..

> @@ -951,7 +1117,7 @@ static int ad7173_fw_parse_channel_config(struct iio_dev *indio_dev)
>         struct device *dev = indio_dev->dev.parent;
>         struct iio_chan_spec *chan_arr, *chan;
>         unsigned int ain[2], chan_index = 0;
> -       int ref_sel, ret, num_channels;
> +       int ref_sel, ret, reg, num_channels;
>
>         num_channels = device_get_child_node_count(dev);
>

Another thing that is missing in this function both for the chips
being added here and the existing chips are channels for _all_
possible inputs. The driver is adding a fixed input channel for the
temperature sensor, as it should. But all of the chips also have a
similar input channel configuration that measures the reference
voltage. Currently, there doesn't seem to be a way to make use of this
feature. I would expect a hard-coded voltage input channel that is
always added for this reference voltage similar to the temperature
channel.

The ad717x chips (except AD7173-8 and AD7176-2) also have a common
mode voltage input ("((AVDD1 − AVSS)/5)") that could work the same.

In the case of the ad717x chips though, it looks like these channels
are not "fixed" like they are in ad411x. It looks like these inputs
can be mixed and matched with AINx inputs and/or each other as
differential pairs. So if that is actually the case, I would expect
the DT bindings for ad717x to look like adi,ad4130.yaml where these
additional input sources are listed in the diff-channels property
instead of having hard-coded channels in the driver like I have
suggested above.

But, as always, fixes for ad717x should be in a separate patch series.
Still, I think adding a hard-coded channel for the reference voltage
input for ad411x chips in this patch makes sense.