Re: [PATCH v3 1/6] dt-bindings: adc: ad7173: add support for ad411x

From: David Lechner
Date: Wed May 29 2024 - 18:04:32 EST

On 5/29/24 8:38 AM, Ceclan, Dumitru wrote:
> On 28/05/2024 20:52, Conor Dooley wrote:
>> On Tue, May 28, 2024 at 03:16:07PM +0300, Ceclan, Dumitru wrote:
>>> On 27/05/2024 20:48, Conor Dooley wrote:
>>>> On Mon, May 27, 2024 at 08:02:34PM +0300, Dumitru Ceclan via B4 Relay wrote:
>>>>> From: Dumitru Ceclan <dumitru.ceclan@xxxxxxxxxx>
>>>>>
>>>>> Add support for: AD4111, AD4112, AD4114, AD4115, AD4116.
>>>>>
>>>>> AD411x family ADCs support a VCOM pin, dedicated for single-ended usage.
>>>>> AD4111/AD4112 support current channels, usage is implemented by
>>>>> specifying channel reg values bigger than 15.
>>>>>
>>>>> Signed-off-by: Dumitru Ceclan <dumitru.ceclan@xxxxxxxxxx>
>>>>> ---
>>>>> .../devicetree/bindings/iio/adc/adi,ad7173.yaml | 122 ++++++++++++++++++++-
>>>>> 1 file changed, 120 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad7173.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad7173.yaml
>>>>> index ea6cfcd0aff4..5b1af382dad3 100644
>>>>> --- a/Documentation/devicetree/bindings/iio/adc/adi,ad7173.yaml
>>>>> +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad7173.yaml
>>>>> @@ -19,7 +19,18 @@ description: |
>>>>> primarily for measurement of signals close to DC but also delivers
>>>>> outstanding performance with input bandwidths out to ~10kHz.
>>>>>
>>>>> + Analog Devices AD411x ADC's:
>>>>> + 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. They integrate an analog front end suitable for processing
>>>>> + fully differential/single-ended and bipolar voltage inputs.
>>>>> +
>>>>> Datasheets for supported chips:
>>>>> + https://www.analog.com/media/en/technical-documentation/data-sheets/AD4111.pdf
>>>>> + https://www.analog.com/media/en/technical-documentation/data-sheets/AD4112.pdf
>>>>> + https://www.analog.com/media/en/technical-documentation/data-sheets/AD4114.pdf
>>>>> + https://www.analog.com/media/en/technical-documentation/data-sheets/AD4115.pdf
>>>>> + https://www.analog.com/media/en/technical-documentation/data-sheets/AD4116.pdf
>>>>> https://www.analog.com/media/en/technical-documentation/data-sheets/AD7172-2.pdf
>>>>> https://www.analog.com/media/en/technical-documentation/data-sheets/AD7172-4.pdf
>>>>> https://www.analog.com/media/en/technical-documentation/data-sheets/AD7173-8.pdf
>>>>> @@ -31,6 +42,11 @@ description: |
>>>>> properties:
>>>>> compatible:
>>>>> enum:
>>>>> + - adi,ad4111
>>>>> + - adi,ad4112
>>>>> + - adi,ad4114
>>>>> + - adi,ad4115
>>>>> + - adi,ad4116
>>>>> - adi,ad7172-2
>>>>> - adi,ad7172-4
>>>>> - adi,ad7173-8
>>>>> @@ -129,10 +145,36 @@ patternProperties:
>>>>> maximum: 15
>>>>>
>>>>> diff-channels:
>>>>> + description: |
>>>>> + For using current channels specify select the current inputs
>>>>> + and enable the adi,current-channel property.
>>>>> +
>>>>> + Family AD411x supports a dedicated VINCOM voltage input.
>>>>> + To select it set the second channel to 16.
>>>>> + (VIN2, VINCOM) -> diff-channels = <2 16>
>>>>> +
>>>>> + There are special values that can be selected besides the voltage
>>>>> + analog inputs:
>>>>> + 21: REF+
>>>>> + 22: REF−
>>>>> + Supported only by AD7172-2, AD7172-4, AD7175-2, AD7175-8, AD7177-2:
>>>>> + 19: ((AVDD1 − AVSS)/5)+
>>>>> + 20: ((AVDD1 − AVSS)/5)−
>>>>> +
>>>>> items:
>>>>> minimum: 0
>>>>> maximum: 31
>>>>>
>>>>> + single-channel:
>>>>> + description: |
>>>>> + Models AD4111 and AD4112 support single-ended current channels.
>>>>> + To select the desired current input, specify the desired input pair:
>>>>> + (IIN2+, IIN2−) -> single-channel = <2>
>>>>> +
>>>>> + items:
>>>>> + minimum: 1
>>>>> + maximum: 16
>>>>> +
>>>>> adi,reference-select:
>>>>> description: |
>>>>> Select the reference source to use when converting on
>>>>> @@ -154,9 +196,26 @@ patternProperties:
>>>>> - avdd
>>>>> default: refout-avss
>>>>>
>>>>> + adi,current-channel:
>>>>> + description: |
>>>>> + Signal that the selected inputs are current channels.
>>>>> + Only available on AD4111 and AD4112.
>>>>> + type: boolean
>>>>> +
>>>>> + adi,channel-type:
>>>>> + description:
>>>>> + Used to differentiate between different channel types as the device
>>>>> + register configurations are the same for all usage types.
>>>>> + Both pseudo-differential and single-ended channels will use the
>>>>> + single-ended specifier.
>>>>> + $ref: /schemas/types.yaml#/definitions/string
>>>>> + enum:
>>>>> + - single-ended
>>>>> + - differential
>>>>> + default: differential
>>>>
>>>> I dunno if my brain just ain't workin' right today, or if this is not
>>>> sufficiently explained, but why is this property needed? You've got
>>>> diff-channels and single-channels already, why can you not infer the
>>>> information you need from them? What should software do with this
>>>> information?
>>>> Additionally, "pseudo-differential" is not explained in this binding.
>>>
>>> In previous thread we arrived to the conclusion single-ended and
>>> pseudo-differential channels should be marked with the flag
>>> "differential=false" in the IIO channel struct. This cannot
>>> really be inferred as any input pair could be used in that
>>> manner and the only difference would be in external wiring.
>>>
>>> Single-channels cannot be used to define such a channel as
>>> two voltage inputs need to be selected. Also, we are already
>>> using single-channel to define the current channels.
>>
>> If I understand correctly, the property could be simplified to a flag
>> then, since it's only the pseudo differential mode that you cannot be
>> sure of?
>> You know when you're single-ended based on single-channel, so the
>> additional info you need is only in the pseudo-differential case.
>>
> Yes, it could just be a boolean flag. The only thing I have against
> that is the awkwardness of having both diff-channels and
> differential=false within a channel definition.
>
> No, there is no uncertainty regarding pseudo-differential, it's
> basically single-ended.
>
> We cannot use single-channel for voltage channels, two voltage
> inputs need to be specified. And again, single-channel will be
> used here for the current channels.

Instead of using diff-channels for single-ended/pseudo-differential
plus a property that says "actually not differential" could we just
add a second common-mode-channel property to specify the second
input pin that is connected to the common mode voltage source?

Just to make sure I'm understanding, single-ended means common mode
voltage is 0V (or AVSS for this chip, I guess) and pseudo-differential
means the common mode voltage is something else other than that.
In other words, single-ended is just a special case of pseudo-differential.
So effectively, no difference that we need to describe?

So something like this could work?


/* a fully differential voltage input channel */
channel@0 {
reg = <0>;
bipolar;
diff-channels = <0 1>; /* VIN0 is +, VIN1 is - */
adi,reference-select = "vref";
};

/* a single-ended voltage input channel */
channel@1 {
reg = <1>;
/* no bipolar since common mode is 0V */
single-channel = <2>; /* VIN2 is input */
common-mode-channel = <3>; /* VIN3 connected to 0V */
};

/* a pseudo-differential voltage input channel */
channel@2 {
reg = <2>;
bipolar; /* since common mode is not 0V */
single-channel = <4>; /* VIN4 is input */
common-mode-channel = <5>; /* VIN5 connected to Vref / 2 */
adi,reference-select = "vref";
};

/* a current input channel */
channel@3 {
reg = <3>;
bipolar;
/* 0 is not the same pin as channel@0 because of
* the adi,current-channel flag */
single-channel = <0>; /* using IIN0+ and IIN0- pins */
adi,current-channel;
};


If we really wanted to go all the way, we could also think about
adding a common-mode-supply property in each channel node to with
a common-mode-channel property to describe the voltage source that
the pin is connected to.