linux-kernel - Re: [PATCH v2 4/4] iio: adc: ad4080: add support for AD4880 dual-channel ADC

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Message-ID: <20260207150440.46d83d48@jic23-huawei>
Date: Sat, 7 Feb 2026 15:04:40 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Antoniu Miclaus <antoniu.miclaus@...log.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich
 <Michael.Hennerich@...log.com>, David Lechner <dlechner@...libre.com>, Nuno
 Sá <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Olivier Moysan
 <olivier.moysan@...s.st.com>, Mark Brown <broonie@...nel.org>,
 <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <linux-spi@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] iio: adc: ad4080: add support for AD4880
 dual-channel ADC

On Fri, 6 Feb 2026 18:07:16 +0200
Antoniu Miclaus <antoniu.miclaus@...log.com> wrote:

> Add support for the AD4880, a dual-channel 20-bit 40MSPS SAR ADC with
> integrated fully differential amplifiers (FDA).
> 
> The AD4880 has two independent ADC channels, each with its own SPI
> configuration interface. The driver uses spi_new_ancillary_device() to
> create an additional SPI device for the second channel, allowing both
> channels to share the same SPI bus with different chip selects.
> 
> Signed-off-by: Antoniu Miclaus <antoniu.miclaus@...log.com>
Hi Antoniu

Just one minor comment from me.

Thanks,

Jonathan

> ---
> Changes in v2:
>   - Use second reg entry instead of custom adi,aux-spi-cs property for
>     secondary channel chip select
>   - Use devm_iio_backend_get_by_index() instead of named backends for
>     multi-channel backend lookup
>   - Separate iio_info structures for single-channel (ad4080) and
>     multi-channel (ad4880) devices
>   - Keep filter_type as shared attribute for single-channel devices,
>     use per-channel only for AD4880
>   - Add separate AD4880_CHANNEL_DEFINE macro with per-channel attributes
> 
>  drivers/iio/adc/ad4080.c | 256 +++++++++++++++++++++++++++++++--------
>  1 file changed, 205 insertions(+), 51 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad4080.c b/drivers/iio/adc/ad4080.c
> index 7cf3b6ed7940..2b26f8a4d548 100644
> --- a/drivers/iio/adc/ad4080.c
> +++ b/drivers/iio/adc/ad4080.c

>
> @@ -617,13 +736,37 @@ static int ad4080_probe(struct spi_device *spi)
>  		return dev_err_probe(dev, ret,
>  				     "failed to get and enable supplies\n");
>  
> -	st->regmap = devm_regmap_init_spi(spi, &ad4080_regmap_config);
> -	if (IS_ERR(st->regmap))
> -		return PTR_ERR(st->regmap);
> +	/* Setup primary SPI device (channel 0) */
> +	st->spi[0] = spi;
> +	st->regmap[0] = devm_regmap_init_spi(spi, &ad4080_regmap_config);
> +	if (IS_ERR(st->regmap[0]))
> +		return PTR_ERR(st->regmap[0]);
>  
> -	st->info = spi_get_device_match_data(spi);
> -	if (!st->info)
> -		return -ENODEV;
> +	/* Setup ancillary SPI device for additional channel (AD4880) */
> +	if (st->info->num_channels > 1) {

I wonder if this would be clearer as a loop?  When there is a 2 channel device
around, a 4 channels one often shows up later.

	for (int i = 1; i < st->info->num_channels; i++) {

> +		u32 reg[2];
> +
> +		ret = device_property_read_u32_array(dev, "reg", reg,
> +						     ARRAY_SIZE(reg));
> +		if (ret)
> +			return dev_err_probe(dev, ret,
> +					     "missing second reg entry for multi-channel device\n");
> +
> +		st->spi[1] = spi_new_ancillary_device(spi, reg[1]);
> +		if (IS_ERR(st->spi[1]))
> +			return dev_err_probe(dev, PTR_ERR(st->spi[1]),
> +					     "failed to register ancillary device\n");
> +
> +		ret = devm_add_action_or_reset(dev, ad4080_unregister_ancillary,
> +					       st->spi[1]);
> +		if (ret)
> +			return ret;
> +
> +		st->regmap[1] = devm_regmap_init_spi(st->spi[1],
> +						     &ad4080_regmap_config);
> +		if (IS_ERR(st->regmap[1]))
> +			return PTR_ERR(st->regmap[1]);
> +	}