linux-kernel - Re: [PATCH v4 5/5] iio: adc: ad7606: add gain calibration support

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Message-ID: <aBz_Nlgx18UK2GIc@smile.fi.intel.com>
Date: Thu, 8 May 2025 22:00:06 +0300
From: Andy Shevchenko <andy@...nel.org>
To: Angelo Dureghello <adureghello@...libre.com>
Cc: Jonathan Cameron <jic23@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v4 5/5] iio: adc: ad7606: add gain calibration support

On Thu, May 08, 2025 at 12:06:09PM +0200, Angelo Dureghello wrote:
> From: Angelo Dureghello <adureghello@...libre.com>
> 
> Add gain calibration support, using resistor values set on devicetree,
> values to be set accordingly with ADC external RFilter, as explained in
> the ad7606c-16 datasheet, rev0, page 37.
> 
> Usage example in the fdt yaml documentation.

...

> +static int ad7606_chan_calib_gain_setup(struct iio_dev *indio_dev)
> +{
> +	struct ad7606_state *st = iio_priv(indio_dev);
> +	unsigned int num_channels = st->chip_info->num_adc_channels;
> +	struct device *dev = st->dev;
> +	int ret;
> +
> +	/*
> +	 * This function is called once, and parses all the channel nodes,
> +	 * so continuing on next channel node on errors, informing of them.
> +	 */
> +	device_for_each_child_node_scoped(dev, child) {
> +		u32 reg, r_gain;
> +
> +		ret = fwnode_property_read_u32(child, "reg", &reg);
> +		if (ret)
> +			continue;

> +		/* Chan reg is a 1-based index. */
> +		if (reg < 1 || reg > num_channels) {
> +			dev_warn(dev, "wrong ch number (ignoring): %d\n", reg);
> +			continue;
> +		}

But this will allow to have a broken DT. This check basically diminishes the
effort of the DT schema validation. If there are limits one still would be able
to create a DT that passes the driver but doesn't pass the validation.

> +		ret = fwnode_property_read_u32(child, "adi,rfilter-ohms",
> +					       &r_gain);
> +		if (ret)
> +			/* Keep the default register value. */
> +			continue;
> +
> +		if (r_gain > AD7606_CALIB_GAIN_MAX) {
> +			dev_warn(dev, "wrong gain calibration value");
> +			continue;
> +		}
> +
> +		ret = st->bops->reg_write(st, AD7606_CALIB_GAIN(reg - 1),
> +			DIV_ROUND_CLOSEST(r_gain, AD7606_CALIB_GAIN_STEP));
> +		if (ret) {
> +			dev_warn(dev, "error writing r_gain");
> +			continue;
> +		}
> +	}
> +
> +	return 0;
> +}

-- 
With Best Regards,
Andy Shevchenko