Re: [PATCH v7 6/6] iio: adc: ad7606: add gain calibration support

[David Lechner <dlechner@baylibre.com>]

On 5/26/25 5:03 AM, Angelo Dureghello wrote:
> From: Angelo Dureghello <adureghello@baylibre.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.
> 
> Tested-by: David Lechner <dlechner@baylibre.com>

Testing this with parallel interface today instead of SPI and found a bug.

> Reviewed-by: Nuno Sá <nuno.sa@analog.com>
> Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
> ---

...

> +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;
> +
> +	device_for_each_child_node_scoped(dev, child) {
> +		u32 reg, r_gain;
> +
> +		ret = fwnode_property_read_u32(child, "reg", &reg);
> +		if (ret)
> +			return ret;
> +
> +		/* Chan reg is a 1-based index. */
> +		if (reg < 1 || reg > num_channels)
> +			return ret;
> +
> +		r_gain = 0;
> +		ret = fwnode_property_read_u32(child, "adi,rfilter-ohms",
> +					       &r_gain);
> +		if (r_gain > AD7606_CALIB_GAIN_MAX)
> +			return -EINVAL;
> +
> +		ret = st->bops->reg_write(st, AD7606_CALIB_GAIN(reg - 1),
> +			DIV_ROUND_CLOSEST(r_gain, AD7606_CALIB_GAIN_STEP));

ad7606_chan_calib_gain_setup() is called before ad7606_reset() so any value
written here will be cleared by the reset.

Also, this is called before st->bops->iio_backend_config() so when using
the parallel bus, this causes a segfault.

The simplest thing to do is probably store the r_gain values and then
create a new function to write that data to the registers and call that
near the end of the probe() function.

> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +