linux-kernel - Re: [PATCH v2 7/8] iio: dac: ds4424: add Rfs-based scale and per-variant limits

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Message-ID: <aXiXdVg6WuyiwBWa@smile.fi.intel.com>
Date: Tue, 27 Jan 2026 12:46:13 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Jonathan Cameron <jic23@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org, Andy Shevchenko <andy@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	David Jander <david@...tonic.nl>
Subject: Re: [PATCH v2 7/8] iio: dac: ds4424: add Rfs-based scale and
 per-variant limits

On Tue, Jan 27, 2026 at 07:09:38AM +0100, Oleksij Rempel wrote:
> Parse optional maxim,rfs-ohms values to derive the per-channel output
> current scale (mA per step) for the IIO current ABI.
> 
> Select per-variant parameters to match the shared register map while
> handling different data widths and full-scale current calculations.
> 
> Behavior changes:
> - If maxim,rfs-ohms is present, IIO_CHAN_INFO_SCALE becomes available
>   and reports mA/step derived from Rfs.
> - If maxim,rfs-ohms is missing, SCALE is not exposed to keep older DTs
>   working without requiring updates.
> - RAW writes are now limited to the representable sign-magnitude range
>   of the detected variant to avoid silent truncation (e.g. +/-31 on
>   DS440x).

...

> +struct ds4424_chip_info {
> +	int vref_mv;

_mV ?

> +	int scale_denom;
> +	u8 result_mask;
> +};

...

> +static int ds4424_setup_channels(struct i2c_client *client,
> +				 struct ds4424_data *data,
> +				 struct iio_dev *indio_dev)
> +{
> +	struct iio_chan_spec *channels;
> +	size_t channels_size;
> +
> +	channels_size = indio_dev->num_channels * sizeof(ds4424_channels[0]);
> +	/* Use a local non-const pointer for modification */
> +	channels = devm_kmemdup(&client->dev, ds4424_channels, channels_size,
> +				GFP_KERNEL);

Why not devm_kmemdup_array()?

> +	if (!channels)
> +		return -ENOMEM;
> +
> +	if (data->has_rfs) {
> +		for (unsigned int i = 0; i < indio_dev->num_channels; i++)
> +			channels[i].info_mask_separate |=
> +				BIT(IIO_CHAN_INFO_SCALE);
> +	}
> +
> +	indio_dev->channels = channels;
> +
> +	return 0;
> +}

...

> +static int ds4424_parse_rfs(struct i2c_client *client,
> +			    struct ds4424_data *data,
> +			    struct iio_dev *indio_dev)
> +{
> +	struct device *dev = &client->dev;
> +	int count, ret;

Can count be negative?

> +	if (!device_property_present(dev, "maxim,rfs-ohms")) {
> +		dev_info_once(dev, "maxim,rfs-ohms missing, scale not supported\n");
> +		return 0;
> +	}
> +
> +	count = device_property_count_u32(dev, "maxim,rfs-ohms");
> +	if (count != indio_dev->num_channels)
> +		return dev_err_probe(dev, -EINVAL, "maxim,rfs-ohms must have %u entries\n",
> +				     indio_dev->num_channels);
> +
> +	ret = device_property_read_u32_array(dev, "maxim,rfs-ohms",
> +					     data->rfs_ohms,
> +					     indio_dev->num_channels);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to read maxim,rfs-ohms property\n");
> +
> +	for (unsigned int i = 0; i < indio_dev->num_channels; i++) {
> +		if (!data->rfs_ohms[i])
> +			return dev_err_probe(dev, -EINVAL, "maxim,rfs-ohms entry %d is zero\n",

%u

> +					     i);

I would leave it on the same line.

> +	}
> +
> +	data->has_rfs = true;
> +
> +	return 0;
> +}

-- 
With Best Regards,
Andy Shevchenko