linux-kernel - Re: [PATCH 1/3] dt-bindings: iio: adc: add AD4695 and similar ADCs

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Message-ID: <b6b52b1e-847b-44ca-87f9-095a78164771@baylibre.com>
Date: Thu, 13 Jun 2024 09:39:20 -0500
From: David Lechner <dlechner@...libre.com>
To: Krzysztof Kozlowski <krzk@...nel.org>, Jonathan Cameron
 <jic23@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>
Cc: Michael Hennerich <michael.hennerich@...log.com>,
 Nuno Sá <nuno.sa@...log.com>,
 Jonathan Corbet <corbet@....net>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org
Subject: Re: [PATCH 1/3] dt-bindings: iio: adc: add AD4695 and similar ADCs

On 6/13/24 9:18 AM, Krzysztof Kozlowski wrote:
> On 13/06/2024 15:57, David Lechner wrote:
>>
>>>
>>>> +          - const: adi,ad4695
>>>> +      - items:
>>>> +          - const: adi,ad4697-wlcsp
>>>> +          - const: adi,ad4697
>>>> +      # same chips with higher max sample rate
>>
>> I suppose one could make the argument that the programming model is
>> the same on these too, but the maximum sampling frequency does seem
>> like an important bit of information so that you don't try to set
>> the conversion trigger rate too high.
>>
> 
> which property is that? I don't see differences in the driver, so I
> don't get how these wlcsp compatibles allow you to control value of
> conversion trigger.

This comment is unrelated to the package type (WLCSP or LFCSP).

What I mean is that e.g. AD4695 and AD4696 are virtually identical
other than the maximum allowable sample rate (500 kSPS or 1 MSPS).

So my thinking was that it would make sense to have:

	compatible = "ad4695";

for the lower sample rate chip and

	compatible = "ad4696", "ad4695";

for the higher sample rate chip since ad4696 can do everything
that ad4695 does plus a bit more.

We haven't implemented buffered reads in the driver yet, so there
isn't anything currently to be seen there. But when we do, we probably
want to limit the allowable value for the sampling_frequency attribute
based on which version of the chip is present. (I would like to get
Jonathan's opinion of if this is something we actually need to do
or not.)