Re: [PATCH v3 8/8] iio: adc: rzt2h: Add support for RZ/V2H(P) SoC

[Andy Shevchenko]

On Fri, Oct 23, 2026 at 06:59:19PM +0100, Prabhakar wrote:

> Add support for the ADC found on the Renesas RZ/V2H(P) SoC, which shares
> the RZ/T2H ADC IP but differs in channel count, sampling, calibration and
> resolution support.
> 
> The RZ/V2H(P) ADC provides 8 channels, has a fixed conversion time of
> 20 ADCLK cycles, does not support calibration, and supports selectable
> 12-bit and 8-bit conversion resolution.
> 
> Expose the fixed sampling frequency as a read-only attribute and allow
> the conversion resolution to be changed through the scale attribute.
> Use extended scan types so the reported scan type follows the selected
> resolution, and prevent resolution changes while buffered capture is
> active.

...

> +static int rzt2h_adc_write_scale(struct iio_dev *indio_dev,
> +				 struct iio_chan_spec const *chan,
> +				 int val, int val2)
> +{
> +	struct rzt2h_adc *adc = iio_priv(indio_dev);
> +	u64 req_scale, scale;
> +	unsigned int i;
> +
> +	if (!(adc->chip_info->features & RZT2H_ADC_FEATURE_RES_SELECT))
> +		return -EINVAL;
> +
> +	req_scale = mul_u32_u32(val, NANO) + val2;

But what's wrong with the simple 1ULL * val * NANO?

> +	for (i = 0; i < chan->num_ext_scan_type; i++) {
> +		scale = mul_u32_u32(RZT2H_ADC_VREF_mV, NANO) >>

Similar Q.

> +			chan->ext_scan_type[i].realbits;
> +		if (scale == req_scale)
> +			break;
> +	}
> +	if (i == chan->num_ext_scan_type)
> +		return -EINVAL;
> +
> +	/* The scan type changes with the resolution. */
> +	IIO_DEV_ACQUIRE_DIRECT_MODE(indio_dev, claim);
> +	if (IIO_DEV_ACQUIRE_FAILED(claim))
> +		return -EBUSY;
> +
> +	adc->resolution = i;
> +
> +	return 0;
> +}

-- 
With Best Regards,
Andy Shevchenko