linux-kernel - Re: [PATCH 08/15] dt-bindings: iio: adc: adi,ad4030: Add 4-lane per channel bus width option

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Message-ID: <b2688cb1-1ec4-46ac-89e3-dae4f919a177@baylibre.com>
Date: Sat, 30 Aug 2025 12:01:42 -0500
From: David Lechner <dlechner@...libre.com>
To: Marcelo Schmitt <marcelo.schmitt@...log.com>, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 devicetree@...r.kernel.org, linux-spi@...r.kernel.org
Cc: jic23@...nel.org, Michael.Hennerich@...log.com, nuno.sa@...log.com,
 eblanc@...libre.com, andy@...nel.org, corbet@....net, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, broonie@...nel.org,
 Jonathan.Cameron@...wei.com, andriy.shevchenko@...ux.intel.com,
 ahaslam@...libre.com, marcelo.schmitt1@...il.com
Subject: Re: [PATCH 08/15] dt-bindings: iio: adc: adi,ad4030: Add 4-lane per
 channel bus width option

On 8/29/25 7:43 PM, Marcelo Schmitt wrote:
> AD4630 has two input channels and each of them can have it's data output in
> 4 dedicated lines, resulting in a total of 8 data lines used by the device.
> Document the option that specifies the case where AD4630 and similar ADCs
> provide data through 8 SPI lines.

It is true that there are 8 serial data out lines, but not all lines
work the same way. spi-rx-bus-width describes the quad-spi-like lines
for sending multiple bits of one word from one channel at the same time.

The second set of 4 lines is for sending data from a separate channel
at the same time, so it doesn't work with an octal SPI without scrambling
data between to two channels.

Instead, I am proposing that we consider the second channel (the 2nd set
of 4 lines) as a second SPI bus on the same SPI controller. I am currently
working on implementing this in the AXI SPI Engine and the AD7380 driver.
There is still some HDL work to finalize for this before I can submit it
to the mailing lists though. 

It will use the bindings proposed in [1] rather than spi-rx-bus-width.
So we should drop this patch and wait for the other work to be done
before supporting reading both channels at the same time on AD4630.

[1]: https://lore.kernel.org/linux-spi/20250616220054.3968946-1-sean.anderson@linux.dev/

> 
> Signed-off-by: Marcelo Schmitt <marcelo.schmitt@...log.com>
> ---
>  Documentation/devicetree/bindings/iio/adc/adi,ad4030.yaml | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad4030.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad4030.yaml
> index 564b6f67a96e..bee85087a7b2 100644
> --- a/Documentation/devicetree/bindings/iio/adc/adi,ad4030.yaml
> +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad4030.yaml
> @@ -39,7 +39,7 @@ properties:
>      maximum: 102040816
>  
>    spi-rx-bus-width:
> -    enum: [1, 2, 4]
> +    enum: [1, 2, 4, 8]
>  
>    vdd-5v-supply: true
>    vdd-1v8-supply: true