linux-kernel - Re: [PATCH v8 7/8] iio: adc: ad4030: Add support for ADAQ4216 and ADAQ4224

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Message-ID: <aYiXKq5SJ3wNl8DA@smile.fi.intel.com>
Date: Sun, 8 Feb 2026 16:01:14 +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 7/8] iio: adc: ad4030: Add support for ADAQ4216 and
 ADAQ4224

On Fri, Feb 06, 2026 at 04:02:19PM -0300, Marcelo Schmitt wrote:
> ADAQ4216 and ADAQ4224 are similar to AD4030, but feature a PGA circuitry
> that scales the analog input signal prior to it reaching the ADC. The PGA
> is controlled through a pair of pins (A0 and A1) whose state define the
> gain that is applied to the input signal.
> 
> Add support for ADAQ4216 and ADAQ4224. Provide a list of PGA options
> through the IIO device channel scale available interface and enable control
> of the PGA through the channel scale interface.

...

> +/*
> + * Gains computed as fractions of 1000 so they can be expressed by integers.
> + */
> +static const int adaq4216_hw_gains_vpv[] = {
> +	1 * MILLI / 3,		/* 333 */
> +	5 * MILLI / 9,		/* 555 */
> +	20 * MILLI / 9,		/* 2222 */
> +	20 * MILLI / 3,		/* 6666 */

In case you would need a new version, or Jonathan is okay to tweak, I think
it's better to use float in the comments. The above comment explains the
MILL multiplier for the values.

	1 * MILLI / 3,		/* 0.333 */
	5 * MILLI / 9,		/* 0.555 */
	20 * MILLI / 9,		/* 0.2222 */
	20 * MILLI / 3,		/* 0.6666 */

> +};

Btw, if this true (if I am not mistaken in the gain values), the question is
why 0.2222 is much higher than 0.555.

-- 
With Best Regards,
Andy Shevchenko