linux-kernel - Re: [PATCH v6 5/5] iio: adc: ad7405: add ad7405 driver

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Message-ID: <9295ffc8-51aa-440f-8d55-0a6f64e6a352@baylibre.com>
Date: Wed, 4 Jun 2025 14:41:47 -0500
From: David Lechner <dlechner@...libre.com>
To: Pop Ioan Daniel <pop.ioan-daniel@...log.com>,
 Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Jonathan Cameron <jic23@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Sergiu Cuciurean <sergiu.cuciurean@...log.com>,
 Dragos Bogdan <dragos.bogdan@...log.com>,
 Antoniu Miclaus <antoniu.miclaus@...log.com>,
 Olivier Moysan <olivier.moysan@...s.st.com>,
 Javier Carrasco <javier.carrasco.cruz@...il.com>,
 Matti Vaittinen <mazziesaccount@...il.com>,
 Tobias Sperling <tobias.sperling@...ting.com>,
 Alisa-Dariana Roman <alisadariana@...il.com>,
 Marcelo Schmitt <marcelo.schmitt@...log.com>,
 Esteban Blanc <eblanc@...libre.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 5/5] iio: adc: ad7405: add ad7405 driver

On 6/4/25 8:34 AM, Pop Ioan Daniel wrote:
> Add support for the AD7405/ADUM770x, a high performance isolated ADC,
> 1-channel, 16-bit with a second-order Σ-Δ modulator that converts an
> analog input signal into a high speed, single-bit data stream.
> 
> Signed-off-by: Pop Ioan Daniel <pop.ioan-daniel@...log.com>
> ---

...

> diff --git a/drivers/iio/adc/ad7405.c b/drivers/iio/adc/ad7405.c
> new file mode 100644
> index 000000000000..a5ca61ad5150
> --- /dev/null
> +++ b/drivers/iio/adc/ad7405.c
> @@ -0,0 +1,262 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Analog Devices AD7405 driver
> + *
> + * Copyright 2025 Analog Devices Inc.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/kernel.h>

Maybe it wasn't clear in previous reviews, but we like to avoid including
kernel.h because it includes too much, so should be replaced with ofher
more specific headers.

> +#include <linux/module.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/platform_device.h>
> +#include <linux/property.h>
> +#include <linux/regulator/consumer.h>
> +#include <linux/util_macros.h>
> +

...

> +
> +static int ad7405_set_dec_rate(struct iio_dev *indio_dev,
> +			       const struct iio_chan_spec *chan,
> +			       unsigned int dec_rate)
> +{
> +	struct ad7405_state *st = iio_priv(indio_dev);
> +	int ret;
> +
> +	if (!iio_device_claim_direct(indio_dev))
> +		return -EBUSY;
> +
> +	if (dec_rate > 4096 || dec_rate < 32)
> +		return -EINVAL;
> +
> +	ret = iio_backend_oversampling_ratio_set(st->back, chan->scan_index, dec_rate);
> +	if (ret)
> +		return ret;
> +
> +	st->dec_rate = dec_rate;
> +
> +	iio_device_release_direct(indio_dev);

iio_device_release_direct() needs to always be called before returning
after iio_backend_oversampling_ratio_set() is called. So this function
needs some reordering.

It should look like:

	if (!iio_device_claim_direct(indio_dev))
		return -EBUSY;

	ret = iio_backend_oversampling_ratio_set(st->back, chan->scan_index, dec_rate);
	iio_device_release_direct(indio_dev);

With everything else before or after that.

Or move the claim/realease to ad7405_write_raw() so that the entire call
to ad7405_set_dec_rate() is syncronized.

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

...

> +static int ad7405_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct iio_dev *indio_dev;
> +	struct ad7405_state *st;
> +	struct clk *clk;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*st));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	st = iio_priv(indio_dev);
> +
> +	st->info = device_get_match_data(dev);
> +	if (!st->info)
> +		return dev_err_probe(dev, -EINVAL, "no chip info\n");
> +
> +	ret = devm_regulator_bulk_get_enable(dev, ARRAY_SIZE(ad7405_power_supplies),
> +					     ad7405_power_supplies);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "failed to get and enable supplies");
> +
> +	clk = devm_clk_get_enabled(dev, NULL);
> +	if (IS_ERR(clk))
> +		return PTR_ERR(clk);
> +
> +	st->ref_frequency = clk_get_rate(clk);
> +	if (!st->ref_frequency)
> +		return -EINVAL;
> +
> +	indio_dev->name = st->info->name;
> +	indio_dev->channels = &st->info->channel;
> +	indio_dev->num_channels = 1;
> +	indio_dev->info = &ad7405_iio_info;
> +
> +	st->back = devm_iio_backend_get(dev, NULL);
> +	if (IS_ERR(st->back))
> +		return dev_err_probe(dev, PTR_ERR(st->back),
> +				     "failed to get IIO backend");
> +
> +	ret = iio_backend_chan_enable(st->back, 0);
> +	if (ret)
> +		return ret;
> +
> +	ret = devm_iio_backend_request_buffer(dev, st->back, indio_dev);
> +	if (ret)
> +		return ret;
> +
> +	ret = devm_iio_backend_enable(dev, st->back);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 *Set 256 decimation rate. The default value in the AXI_ADC register

Add space after * to match IIO comment style.

> +	 *is 0, so we set the register with a decimation rate value that is
> +	 *functional for all parts.
> +	 */
> +	ret = ad7405_set_dec_rate(indio_dev, &indio_dev->channels[0], 256);
> +	if (ret)
> +		return ret;
> +
> +	return devm_iio_device_register(dev, indio_dev);
> +}