linux-kernel - Re: [PATCH v8 8/8] iio: adc: ad4030: Support common-mode channels with SPI offloading

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Message-ID: <aYiXjCpiMQ_h9Ao4@smile.fi.intel.com>
Date: Sun, 8 Feb 2026 16:02:52 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Marcelo Schmitt <marcelo.schmitt@...log.com>
Cc: linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	jic23@...nel.org, michael.hennerich@...log.com, nuno.sa@...log.com,
	eblanc@...libre.com, dlechner@...libre.com, andy@...nel.org,
	robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
	corbet@....net, marcelo.schmitt1@...il.com
Subject: Re: [PATCH v8 8/8] iio: adc: ad4030: Support common-mode channels
 with SPI offloading

On Fri, Feb 06, 2026 at 04:02:42PM -0300, Marcelo Schmitt wrote:
> AD4030 and similar devices can read common-mode voltage together with
> ADC sample data. When enabled, common-mode voltage data is provided in a
> separate IIO channel since it measures something other than the primary
> ADC input signal and requires separate scaling to convert to voltage
> units. The initial SPI offload support patch for AD4030 only provided
> differential channels. Now, extend the AD4030 driver to also provide
> common-mode IIO channels when setup with SPI offloading capability.

...

> -#define AD4030_CHAN_CMO(_idx, _ch)  {					\
> +#define __AD4030_CHAN_CMO(_idx, _ch, _offload)  {			\
>  	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |			\
>  		BIT(IIO_CHAN_INFO_SCALE),				\
>  	.type = IIO_VOLTAGE,						\

>  	.scan_index = (_idx),						\
>  	.scan_type = {							\
>  		.sign = 'u',						\
> -		.storagebits = 8,					\
> +		.storagebits = (_offload ? 32 : 8),			\
>  		.realbits = 8,						\
> -		.endianness = IIO_BE,					\
> +		.endianness = (_offload ? IIO_CPU : IIO_BE),		\

Hmm... This is interesting. Does it mean it's designed like this for any
offloaded SPI case? Wouldn't be better to follow the same endianess in both?

>  	},								\
>  }


-- 
With Best Regards,
Andy Shevchenko