linux-kernel - Re: [PATCH 2/8] dt-bindings: iio: adc: ad7606: Add iio backend bindings

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Message-ID: <b7cae260-19ca-485d-b9c5-4b9209ee4886@baylibre.com>
Date: Wed, 4 Sep 2024 11:54:30 -0500
From: David Lechner <dlechner@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>, Guillaume Stols <gstols@...libre.com>
Cc: Uwe Kleine-König <ukleinek@...nel.org>,
 Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>, Jonathan Corbet <corbet@....net>,
 linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-fbdev@...r.kernel.org, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-doc@...r.kernel.org, aardelean@...libre.com
Subject: Re: [PATCH 2/8] dt-bindings: iio: adc: ad7606: Add iio backend
 bindings

On 8/17/24 10:09 AM, Jonathan Cameron wrote:
> On Thu, 15 Aug 2024 12:11:56 +0000
> Guillaume Stols <gstols@...libre.com> wrote:
> 
>> Add the required properties for iio-backend support, as well as an
>> example and the conditions to mutually exclude interruption and
>> conversion trigger with iio-backend.
>> The iio-backend's function is to controls the communication, and thus the
>> interruption pin won't be available anymore.
>> As a consequence, the conversion pin must be controlled externally since
>> we will miss information about when every single conversion cycle (i.e
>> conversion + data transfert) ends, hence a PWM is introduced to trigger
> 
> transfer
> 
>> the conversions.
>>
>> Signed-off-by: Guillaume Stols <gstols@...libre.com>
>> ---
>>  .../devicetree/bindings/iio/adc/adi,ad7606.yaml    | 75 +++++++++++++++++++++-
>>  1 file changed, 72 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad7606.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad7606.yaml
>> index c0008d36320f..4b324f7e3207 100644
>> --- a/Documentation/devicetree/bindings/iio/adc/adi,ad7606.yaml
>> +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad7606.yaml
>> @@ -114,13 +114,28 @@ properties:
>>        assumed that the pins are hardwired to VDD.
>>      type: boolean
>>  
>> +  pwms:
>> +    description:
>> +      In case the conversion is triggered by a PWM instead of a GPIO plugged to
>> +      the CONVST pin, the PWM must be referenced.
>> +    minItems: 1
>> +    maxItems: 2
>> +
>> +  pwm-names:
>> +    minItems: 1
>> +    maxItems: 2
>> +
>> +  io-backends:
>> +    description:
>> +      A reference to the iio-backend, which is responsible handling the BUSY
>> +      pin's falling edge and communication.
>> +      An example of backend can be found at
>> +      http://analogdevicesinc.github.io/hdl/library/axi_ad7606x/index.html
>> +
>>  required:
>>    - compatible
>> -  - reg
> 
> I think we still want a reg, but only to differentiate multiple instances
> perhaps.

In light of the recent discussions on the similar AXI DAC
support for AD3552R [1], should we consider some of the same
things here?

Essentially, the AXI ADC IP block in this series is acting as
a parallel bus provider for the AD7606 chip. This is used both
for configuring registers on the chip and "offloading" for high
speed data capture.

So this would mean...

1. We should add a new compatible string to iio/adc/adi,axi-adc.yaml
   for the specialized version of the AXI ADC IP that is used with
   AD7606 and similar ADCs.
2. In the .dts, the AXI ADC node should be the parent of the ADC node
   since the AXI ADC IP is providing the parallel bus to the ADC.

[1]: https://lore.kernel.org/linux-iio/20240903203935.358a1423@jic23-huawei/

> 
>>    - avcc-supply
>>    - vdrive-supply
> 
> 
>