linux-kernel - Re: [PATCH v5 02/14] dt-bindings: iio: adc: ad7768-1: add trigger-sources property

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Message-ID: <d6a636c7-36df-4648-92a1-2db1ff4754e6@baylibre.com>
Date: Thu, 17 Apr 2025 10:07:50 -0500
From: David Lechner <dlechner@...libre.com>
To: 3027a9b0-cf4a-4e55-80a7-7f0dd2a008e4@...libre.com
Cc: Jonathan Santos <Jonathan.Santos@...log.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-gpio@...r.kernel.org, lars@...afoo.de, Michael.Hennerich@...log.com,
 marcelo.schmitt@...log.com, jic23@...nel.org, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, marcelo.schmitt1@...il.com,
 linus.walleij@...aro.org, brgl@...ev.pl, lgirdwood@...il.com,
 broonie@...nel.org
Subject: Re: [PATCH v5 02/14] dt-bindings: iio: adc: ad7768-1: add
 trigger-sources property

On 4/16/25 7:22 PM, Jonathan Santos wrote:
> On 04/11, David Lechner wrote:
>> On 4/11/25 10:56 AM, Jonathan Santos wrote:
>>> In addition to GPIO synchronization, The AD7768-1 also supports
>>> synchronization over SPI, which use is recommended when the GPIO
>>> cannot provide a pulse synchronous with the base MCLK signal. It
>>> consists of looping back the SYNC_OUT to the SYNC_IN pin and send
>>> a command via SPI to trigger the synchronization.
>>>
>>> Introduce the 'trigger-sources' property to support SPI-based
>>> synchronization, along with additional optional entries for the SPI
>>> offload trigger and the START signal via GPIO3.
>>>
>>> While at it, add description to the interrupts property.
>>>
>>> Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
>>> ---
>>
>> ...
>>
>>> @@ -57,6 +80,15 @@ properties:
>>>    "#io-channel-cells":
>>>      const: 1
>>>  
>>> +  "#trigger-source-cells":
>>> +    description: |
>>> +      Indicates the trigger source type for each entry:
>>> +      0 = Synchronization GPIO-based trigger
>>> +      1 = Synchronization device trigger (e.g., another ad7768-1)
>>> +      2 = GPIO3 pin acting as START signal
>>> +      3 = DRDY pin acting as SPI offload trigger
>>> +    const: 1
>>> +
>>
>> 0 and 1 don't sound like trigger outputs that this ADC is providing, so don't
>> seem appropriate here. But the SYNC_OUT pin is missing from this list.
>>
>> Also, outputs could be used to trigger anything, not just SPI offload, so don't
>> need to mention that.
> 
> You mean like this:
> 
> ...
>   "#trigger-source-cells":
>     description: |
>       Cell indicates the trigger output signal: 0 = SYNC_OUT, 1 = GPIO3,
>       2 = DRDY.
> 
>     const: 1
> ...
> 
> It would be like interfacing those output pins for a generic trigger
> usage?
> 
>>

Yes this looks correct now.

I don't think this is the case, but in general, if GPIO3 could be programmed
to have different trigger signals, then we would need a 2nd cell. But IIRC,
it can only be the START signal, so 1 cell should be sufficient in this case.