Re: [PATCH v4 5/5] iio: adc: ad4080: add support for AD4880 dual-channel ADC

[Andy Shevchenko]

On Mon, Feb 23, 2026 at 06:21:04PM +0200, Antoniu Miclaus 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.

...

> +static int ad4880_update_scan_mode(struct iio_dev *indio_dev,
> +				   const unsigned long *scan_mask)
> +{
> +	struct ad4080_state *st = iio_priv(indio_dev);
> +	unsigned int ch;

Not used outside of the loop, hence

> +	int ret;
> +
> +	for (ch = 0; ch < st->info->num_channels; ch++) {

	for (unsigned int ch = 0; ch < st->info->num_channels; ch++) {

should suffice.

> +		/*
> +		 * Each backend has a single channel (channel 0 from the
> +		 * backend's perspective), so always use channel index 0.
> +		 */
> +		if (test_bit(ch, scan_mask))
> +			ret = iio_backend_chan_enable(st->back[ch], 0);
> +		else
> +			ret = iio_backend_chan_disable(st->back[ch], 0);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}

...

> +static int ad4080_setup(struct iio_dev *indio_dev)
> +{
> +	struct ad4080_state *st = iio_priv(indio_dev);
> +	unsigned int ch;
> +	int ret;
> +
> +	for (ch = 0; ch < st->info->num_channels; ch++) {

Same.

> +		ret = ad4080_setup_channel(st, ch);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
>  }

...

> +	/* Setup ancillary SPI devices for additional channels */

> +	if (st->info->num_channels > 1) {

Isn't this an exact check the for-loop performs the first?

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

Why is 'i' signed? And why not name it 'ch'?

> +			st->spi[i] = devm_spi_new_ancillary_device(spi,
> +					spi_get_chipselect(spi, i));
> +			if (IS_ERR(st->spi[i]))
> +				return dev_err_probe(dev, PTR_ERR(st->spi[i]),
> +						     "failed to register ancillary device\n");
> +
> +			st->regmap[i] = devm_regmap_init_spi(st->spi[i],
> +							     &ad4080_regmap_config);
> +			if (IS_ERR(st->regmap[i]))
> +				return PTR_ERR(st->regmap[i]);
> +		}
> +	}

...

> +	/* Get backends for all channels */
> +	for (ch = 0; ch < st->info->num_channels; ch++) {

	for (unsigned int ch = 0; ch < st->info->num_channels; ch++) {

?

> +		st->back[ch] = devm_iio_backend_get_by_index(dev, ch);
> +		if (IS_ERR(st->back[ch]))
> +			return PTR_ERR(st->back[ch]);
>  
> +		ret = devm_iio_backend_enable(dev, st->back[ch]);
> +		if (ret)
> +			return ret;
> +	}

-- 
With Best Regards,
Andy Shevchenko