Message-ID: <51C590B5.2060308@kernel.org>
Date:	Sat, 22 Jun 2013 12:55:33 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
CC:	Shawn Guo <shawn.guo@...aro.org>,
	Grant Likely <grant.likely@...retlab.ca>, jimwall@...om,
	brian@...stalfontz.com,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	devicetree-discuss@...ts.ozlabs.org,
	Jonathan Cameron <jic23@....ac.uk>,
	Rob Landley <rob@...dley.net>,
	Rob Herring <rob.herring@...xeda.com>
Subject: Re: [PATCHv2 1/3] iio: Add Nuvoton NAU7802 ADC driver

On 06/20/2013 07:57 PM, Alexandre Belloni wrote:
> The Nuvoton NAU7802 ADC is a 24-bit 2-channels I2C ADC, with adjustable
> gain and sampling rates.
>
Sorry, somewhat low on time today so only a quick review.

1) Missing userspace ABI documentation.  Also, perhaps min_conversions is
   a little vague?  Not that I have a better idea!

2) A lot of i2c calls could do with error handling.


> Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> ---
>  .../bindings/iio/adc/nuvoton-nau7802.txt           |  17 +
>  drivers/iio/adc/Kconfig                            |   9 +
>  drivers/iio/adc/Makefile                           |   1 +
>  drivers/iio/adc/nau7802.c                          | 603 +++++++++++++++++++++
>  4 files changed, 630 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/adc/nuvoton-nau7802.txt
>  create mode 100644 drivers/iio/adc/nau7802.c
>
> diff --git a/Documentation/devicetree/bindings/iio/adc/nuvoton-nau7802.txt b/Documentation/devicetree/bindings/iio/adc/nuvoton-nau7802.txt
> new file mode 100644
> index 0000000..9bc4218
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/nuvoton-nau7802.txt
> @@ -0,0 +1,17 @@
> +* Nuvoton NAU7802 Analog to Digital Converter (ADC)
> +
> +Required properties:
> +  - compatible: Should be "nuvoton,nau7802"
> +  - reg: Should contain the ADC I2C address
> +
> +Optional properties:
> +  - nuvoton,vldo: Reference voltage in millivolts (integer)
> +  - interrupts: IRQ line for the ADC. If not used the driver will use
> +    polling.
> +
> +Example:
> +adc2: nau7802@2a {
> +	compatible = "nuvoton,nau7802";
> +	reg = <0x2a>;
> +	nuvoton,vldo = <3000>;
> +};
> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> index ab0767e6..d7f9ed8 100644
> --- a/drivers/iio/adc/Kconfig
> +++ b/drivers/iio/adc/Kconfig
> @@ -133,6 +133,15 @@ config MAX1363
>  	  max11646, max11647) Provides direct access via sysfs and buffered
>  	  data via the iio dev interface.
>
> +config NAU7802
> +	tristate "Nuvoton NAU7802 ADC driver"
> +	depends on I2C
> +	help
> +	  Say yes here to build support for Nuvoton NAU7802 ADC.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called nau7802.
> +
>  config TI_ADC081C
>  	tristate "Texas Instruments ADC081C021/027"
>  	depends on I2C
> diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
> index 0a825be..d426081 100644
> --- a/drivers/iio/adc/Makefile
> +++ b/drivers/iio/adc/Makefile
> @@ -14,6 +14,7 @@ obj-$(CONFIG_AT91_ADC) += at91_adc.o
>  obj-$(CONFIG_EXYNOS_ADC) += exynos_adc.o
>  obj-$(CONFIG_LP8788_ADC) += lp8788_adc.o
>  obj-$(CONFIG_MAX1363) += max1363.o
> +obj-$(CONFIG_NAU7802) += nau7802.o
>  obj-$(CONFIG_TI_ADC081C) += ti-adc081c.o
>  obj-$(CONFIG_TI_AM335X_ADC) += ti_am335x_adc.o
>  obj-$(CONFIG_VIPERBOARD_ADC) += viperboard_adc.o
> diff --git a/drivers/iio/adc/nau7802.c b/drivers/iio/adc/nau7802.c
> new file mode 100644
> index 0000000..e1b6981
> --- /dev/null
> +++ b/drivers/iio/adc/nau7802.c
> @@ -0,0 +1,603 @@
> +/*
> + * Driver for the Nuvoton NAU7802 ADC
> + *
> + * Copyright 2013 Free Electrons
> + *
> + * Licensed under the GPLv2 or later.
> + */
> +
> +#include <linux/delay.h>
> +#include <linux/i2c.h>
> +#include <linux/interrupt.h>
> +#include <linux/module.h>
> +#include <linux/wait.h>
> +#include <linux/log2.h>
> +
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
> +
> +#define NAU7802_REG_PUCTRL	0x00
> +#define NAU7802_PUCTRL_RR(x)		(x << 0)
> +#define NAU7802_PUCTRL_RR_BIT		NAU7802_PUCTRL_RR(1)
> +#define NAU7802_PUCTRL_PUD(x)		(x << 1)
> +#define NAU7802_PUCTRL_PUD_BIT		NAU7802_PUCTRL_PUD(1)
> +#define NAU7802_PUCTRL_PUA(x)		(x << 2)
> +#define NAU7802_PUCTRL_PUA_BIT		NAU7802_PUCTRL_PUA(1)
> +#define NAU7802_PUCTRL_PUR(x)		(x << 3)
> +#define NAU7802_PUCTRL_PUR_BIT		NAU7802_PUCTRL_PUR(1)
> +#define NAU7802_PUCTRL_CS(x)		(x << 4)
> +#define NAU7802_PUCTRL_CS_BIT		NAU7802_PUCTRL_CS(1)
> +#define NAU7802_PUCTRL_CR(x)		(x << 5)
> +#define NAU7802_PUCTRL_CR_BIT		NAU7802_PUCTRL_CR(1)
> +#define NAU7802_PUCTRL_AVDDS(x)		(x << 7)
> +#define NAU7802_PUCTRL_AVDDS_BIT	NAU7802_PUCTRL_AVDDS(1)
> +#define NAU7802_REG_CTRL1	0x01
> +#define NAU7802_CTRL1_VLDO(x)		(x << 3)
> +#define NAU7802_CTRL1_GAINS(x)		(x)
> +#define NAU7802_CTRL1_GAINS_BITS	0x07
> +#define NAU7802_REG_CTRL2	0x02
> +#define NAU7802_CTRL2_CHS(x)		(x << 7)
> +#define NAU7802_CTRL2_CRS(x)		(x << 4)
> +#define NAU7802_SAMP_FREQ_320	0x07
> +#define NAU7802_CTRL2_CHS_BIT		NAU7802_CTRL2_CHS(1)
> +#define NAU7802_REG_ADC_B2	0x12
> +#define NAU7802_REG_ADC_B1	0x13
> +#define NAU7802_REG_ADC_B0	0x14
> +#define NAU7802_REG_ADC_CTRL	0x15
> +
> +#define NAU7802_DEFAULT_CONVERSIONS 6
> +
> +struct nau7802_state {
> +	struct i2c_client	*client;
> +	s32			last_value;
> +	struct mutex		lock;
> +	struct mutex		data_lock;
> +	u32			vref_mv;
> +	u32			conversion_count;
> +	u32			min_conversions;
> +	u8			sample_rate;
> +	u32			scale_avail[8];
> +	struct completion	value_ok;
> +};
> +
> +#define NAU7802_CHANNEL(chan) {					\
> +	.type = IIO_VOLTAGE,					\
> +	.indexed = 1,						\
> +	.channel = (chan),					\
> +	.scan_index = (chan),					\
> +	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
> +	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |	\
> +				BIT(IIO_CHAN_INFO_SAMP_FREQ)	\
> +}
> +
> +static const struct iio_chan_spec nau7802_chan_array[] = {
> +	NAU7802_CHANNEL(0),
> +	NAU7802_CHANNEL(1),
> +};
> +
> +static const u16 nau7802_sample_freq_avail[] = {10, 20, 40, 80,
> +						10, 10, 10, 320};
> +
> +static IIO_CONST_ATTR_SAMP_FREQ_AVAIL("10 40 80 320");
> +
> +static ssize_t nau7802_sysfs_set_min_conversions(struct device *dev,
> +		struct device_attribute *attr,
> +		const char *buf,
> +		size_t len)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct nau7802_state *st = iio_priv(indio_dev);
> +	u32 val;
> +	int ret;
> +
> +	ret = kstrtouint(buf, 10, &val);
> +	if (ret)
> +		return ret;
> +
> +	mutex_lock(&st->lock);
> +	st->min_conversions = val;
> +	st->conversion_count = 0;
> +	mutex_unlock(&st->lock);
> +
> +	return len;
> +}
> +
> +static ssize_t nau7802_sysfs_get_min_conversions(struct device *dev,
> +		struct device_attribute *attr,
> +		char *buf)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct nau7802_state *st = iio_priv(indio_dev);
> +
> +	return sprintf(buf, "%d\n", st->min_conversions);
> +}
> +
> +static IIO_DEVICE_ATTR(min_conversions, S_IWUSR | S_IRUGO,
> +		nau7802_sysfs_get_min_conversions,
> +		nau7802_sysfs_set_min_conversions, 0);
> +
> +static struct attribute *nau7802_attributes[] = {
> +	&iio_const_attr_sampling_frequency_available.dev_attr.attr,
> +	&iio_dev_attr_min_conversions.dev_attr.attr,
A new userspace abi element so it needs documented under
Documentaiton/ABI/testing/
> +	NULL
> +};
> +
> +static const struct attribute_group nau7802_attribute_group = {
> +	.attrs = nau7802_attributes,
> +};
> +
> +static int nau7802_set_gain(struct nau7802_state *st, int gain)
> +{
> +	u8 data;
> +	int ret;
> +
> +	mutex_lock(&st->lock);
> +	st->conversion_count = 0;
> +
> +	data = i2c_smbus_read_byte_data(st->client, NAU7802_REG_CTRL1);
> +	if (data < 0)
> +		goto nau7802_sysfs_set_gain_out;
> +	ret = i2c_smbus_write_byte_data(st->client, NAU7802_REG_CTRL1,
> +					(data & (~NAU7802_CTRL1_GAINS_BITS)) |
> +					gain);
> +
> +nau7802_sysfs_set_gain_out:
> +	mutex_unlock(&st->lock);
> +
> +	return ret ? ret : 0;
> +}
> +
> +static int nau7802_read_conversion(struct nau7802_state *st)
> +{
> +	u8 data;
> +
> +	mutex_lock(&st->data_lock);
> +	data = i2c_smbus_read_byte_data(st->client, NAU7802_REG_ADC_B2);
> +	if (data < 0)
> +		goto nau7802_read_conversion_out;
> +	st->last_value = data << 16;
> +
> +	data = i2c_smbus_read_byte_data(st->client, NAU7802_REG_ADC_B1);
> +	if (data < 0)
> +		goto nau7802_read_conversion_out;
> +	st->last_value |= data << 8;
> +
> +	data = i2c_smbus_read_byte_data(st->client, NAU7802_REG_ADC_B0);
> +	if (data < 0)
> +		goto nau7802_read_conversion_out;
> +	st->last_value |= data;
> +
> +	st->last_value = sign_extend32(st->last_value, 23);
> +
> +nau7802_read_conversion_out:
> +	mutex_unlock(&st->data_lock);
> +
> +	return data;
> +}
> +
> +/*
> + * Conversions are synchronised on the rising edge of NAU7802_PUCTRL_CS_BIT
> + */
> +static int nau7802_sync(struct nau7802_state *st)
> +{
> +	int ret;
> +	u8 data;
> +
> +	data = i2c_smbus_read_byte_data(st->client, NAU7802_REG_PUCTRL);
> +	if (data < 0)
> +		return data;
> +	ret = i2c_smbus_write_byte_data(st->client, NAU7802_REG_PUCTRL,
> +				data | NAU7802_PUCTRL_CS_BIT);
> +
> +	return ret;
> +}
> +
> +static irqreturn_t nau7802_eoc_trigger(int irq, void *private)
> +{
> +	struct iio_dev *indio_dev = private;
> +	struct nau7802_state *st = iio_priv(indio_dev);
> +	u8 status;
> +
> +	status = i2c_smbus_read_byte_data(st->client, NAU7802_REG_PUCTRL);
> +	if (status < 0)
> +		return IRQ_HANDLED;
> +
> +	if (!(status & NAU7802_PUCTRL_CR_BIT))
> +		return IRQ_NONE;
> +
> +	if (nau7802_read_conversion(st) < 0)
> +		return IRQ_HANDLED;
> +
> +	/* Because there is actually only one ADC for both channels, we have to
> +	 * wait for enough conversions to happen before getting a significant
> +	 * value when changing channels and the values are far appart.
> +	 */
> +	if (st->conversion_count < st->min_conversions)
> +		st->conversion_count++;
> +	if (st->conversion_count >= st->min_conversions)
> +		complete_all(&st->value_ok);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int nau7802_read_irq(struct iio_dev *indio_dev,
> +			struct iio_chan_spec const *chan,
> +			int *val)
> +{
> +	struct nau7802_state *st = iio_priv(indio_dev);
> +	int ret;
> +
> +	INIT_COMPLETION(st->value_ok);
> +	enable_irq(st->client->irq);
> +
> +	nau7802_sync(st);
> +
> +	/* read registers to ensure we flush everything */
> +	ret = nau7802_read_conversion(st);
> +	if (ret < 0)
> +		goto read_chan_info_failure;
> +
> +	/* Wait for a conversion to finish */
> +	ret = wait_for_completion_interruptible_timeout(&st->value_ok,
> +			msecs_to_jiffies(1000));
> +	if (ret == 0)
> +		ret = -ETIMEDOUT;
> +
> +	if (ret < 0)
> +		goto read_chan_info_failure;
> +
> +	disable_irq(st->client->irq);
> +
> +	*val = st->last_value;
> +
> +	return IIO_VAL_INT;
> +
> +read_chan_info_failure:
> +	disable_irq(st->client->irq);
> +
> +	return ret;
> +}
> +
> +static int nau7802_read_poll(struct iio_dev *indio_dev,
> +			struct iio_chan_spec const *chan,
> +			int *val)
> +{
> +	struct nau7802_state *st = iio_priv(indio_dev);
> +	int ret;
> +	u8 data;
> +
> +	nau7802_sync(st);
> +
> +	/* read registers to ensure we flush everything */
> +	ret = nau7802_read_conversion(st);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Because there is actually only one ADC for both channels, we have to
> +	 * wait for enough conversions to happen before getting a significant
> +	 * value when changing channels and the values are far appart.
apart
> +	 */
> +	do {
> +		data = i2c_smbus_read_byte_data(st->client, NAU7802_REG_PUCTRL);
> +		if (data < 0)
> +			return data;
> +
> +		while (!(data & NAU7802_PUCTRL_CR_BIT)) {
> +			if (st->sample_rate != NAU7802_SAMP_FREQ_320)
> +				msleep(20);
> +			else
> +				mdelay(4);
> +			data = i2c_smbus_read_byte_data(st->client,
> +							NAU7802_REG_PUCTRL);
> +			if (data < 0)
> +				return data;
> +		}
> +
> +		nau7802_read_conversion(st);
> +		if (ret < 0)
> +			return ret;
> +		if (st->conversion_count < st->min_conversions)
> +			st->conversion_count++;
> +	} while (st->conversion_count < st->min_conversions);
> +
> +	*val = st->last_value;
> +
> +	return IIO_VAL_INT;
> +}
> +
> +static int nau7802_read_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int *val, int *val2, long mask)
> +{
> +	struct nau7802_state *st = iio_priv(indio_dev);
> +	u8 data;
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		mutex_lock(&st->lock);
> +		/*
> +		 * Select the channel to use
> +		 *   - Channel 1 is value 0 in the CHS register
> +		 *   - Channel 2 is value 1 in the CHS register
> +		 */
> +		data = i2c_smbus_read_byte_data(st->client, NAU7802_REG_CTRL2);
> +		if (data < 0)
> +			return data;
> +
> +		if (((data & NAU7802_CTRL2_CHS_BIT) && !chan->channel) ||
> +				(!(data & NAU7802_CTRL2_CHS_BIT) &&
> +				 chan->channel)) {
> +			st->conversion_count = 0;
> +			ret = i2c_smbus_write_byte_data(st->client,
> +					NAU7802_REG_CTRL2,
> +					NAU7802_CTRL2_CHS(chan->channel) |
> +					NAU7802_CTRL2_CRS(st->sample_rate));
> +
> +			if (ret < 0)
> +				return ret;
> +		}
> +
> +		if (st->client->irq)
> +			ret = nau7802_read_irq(indio_dev, chan, val);
> +		else
> +			ret = nau7802_read_poll(indio_dev, chan, val);
> +
> +		mutex_unlock(&st->lock);
> +		return ret;
> +
> +	case IIO_CHAN_INFO_SCALE:
> +		data = i2c_smbus_read_byte_data(st->client, NAU7802_REG_CTRL1);
> +		if (data < 0)
> +			return data;
> +
> +		/* we have 24 bits of signed data, that means 23 bits of data
> +		 * plus the sign bit */
> +		*val = st->vref_mv;
> +		*val2 = 23 + (data & NAU7802_CTRL1_GAINS_BITS);
> +
> +		return IIO_VAL_FRACTIONAL_LOG2;
> +
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		*val =  nau7802_sample_freq_avail[st->sample_rate];
> +		*val2 = 0;
> +		return IIO_VAL_INT;
> +
> +	default:
> +		break;
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static int nau7802_write_raw(struct iio_dev *indio_dev,
> +			     struct iio_chan_spec const *chan,
> +			     int val, int val2, long mask)
> +{
> +	struct nau7802_state *st = iio_priv(indio_dev);
> +	int i;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SCALE:
> +		for (i = 0; i < ARRAY_SIZE(st->scale_avail); i++)
> +			if (val2 == st->scale_avail[i])
> +				return nau7802_set_gain(st, i);
> +
> +		break;
> +
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		for (i = 0; i < ARRAY_SIZE(nau7802_sample_freq_avail); i++)
> +			if (val == nau7802_sample_freq_avail[i]) {
> +				mutex_lock(&st->lock);
> +				st->sample_rate = i;
> +				st->conversion_count = 0;
Error handling for the i2c call?
> +				i2c_smbus_write_byte_data(st->client,
> +					NAU7802_REG_CTRL2,
> +					NAU7802_CTRL2_CRS(st->sample_rate));
> +				mutex_unlock(&st->lock);
> +				return 0;
> +			}
> +
> +		break;
> +
> +	default:
> +		break;
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static int nau7802_write_raw_get_fmt(struct iio_dev *indio_dev,
> +				     struct iio_chan_spec const *chan,
> +				     long mask)
> +{
> +	return IIO_VAL_INT_PLUS_NANO;
> +}
> +
> +static const struct iio_info nau7802_info = {
> +	.driver_module = THIS_MODULE,
> +	.read_raw = &nau7802_read_raw,
> +	.write_raw = &nau7802_write_raw,
> +	.write_raw_get_fmt = nau7802_write_raw_get_fmt,
> +	.attrs = &nau7802_attribute_group,
> +};
> +
> +static int nau7802_probe(struct i2c_client *client,
> +			const struct i2c_device_id *id)
> +{
> +	struct iio_dev *indio_dev;
> +	struct nau7802_state *st;
> +	struct device_node *np = client->dev.of_node;
> +	int i, ret;
> +	u8 data;
> +	u32 tmp;
> +
> +	if (!client->dev.of_node) {
> +		dev_err(&client->dev, "No device tree node available.\n");
> +		return -EINVAL;
> +	}
> +
> +	indio_dev = iio_device_alloc(sizeof(*st));
> +	if (indio_dev == NULL)
> +		return -ENOMEM;
> +
> +	st = iio_priv(indio_dev);
> +
> +	i2c_set_clientdata(client, indio_dev);
> +
> +	indio_dev->dev.parent = &client->dev;
> +	indio_dev->name = dev_name(&client->dev);
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->info = &nau7802_info;
> +
> +	st->client = client;
> +
> +	/* Reset the device */
As a general rule we'd expect any errors returned by these functions
to be checked and handled.
> +	i2c_smbus_write_byte_data(st->client, NAU7802_REG_PUCTRL,
> +				  NAU7802_PUCTRL_RR_BIT);
> +
> +	/* Enter normal operation mode */
> +	i2c_smbus_write_byte_data(st->client, NAU7802_REG_PUCTRL,
> +				  NAU7802_PUCTRL_PUD_BIT);
> +
> +	/*
> +	 * After about 200 usecs, the device should be ready and then
> +	 * the Power Up bit will be set to 1. If not, wait for it.
> +	 */
> +	udelay(210);
> +	data = i2c_smbus_read_byte_data(st->client, NAU7802_REG_PUCTRL);
> +	if (data < 0)
> +		return -ENODEV;
> +	if (!(data & NAU7802_PUCTRL_PUR_BIT))
> +		return -ENODEV;
> +
> +	of_property_read_u32(np, "nuvoton,vldo", &tmp);
> +	st->vref_mv = tmp;
> +
> +	/* Populate available ADC input ranges */
> +	for (i = 0; i < ARRAY_SIZE(st->scale_avail); i++)
> +		st->scale_avail[i] = (((u64)st->vref_mv) * 1000000000ULL)
> +					   >> (23 + i);
> +
> +	data = NAU7802_PUCTRL_PUD_BIT | NAU7802_PUCTRL_PUA_BIT |
> +		NAU7802_PUCTRL_CS_BIT;
> +	if (tmp >= 2400)
> +		data |= NAU7802_PUCTRL_AVDDS_BIT;
> +
> +	i2c_smbus_write_byte_data(st->client, NAU7802_REG_PUCTRL, data);
> +	i2c_smbus_write_byte_data(st->client, NAU7802_REG_ADC_CTRL, 0x30);
> +
> +	if (tmp >= 2400) {
> +		data = NAU7802_CTRL1_VLDO((4500 - tmp) / 300);
> +		i2c_smbus_write_byte_data(st->client, NAU7802_REG_CTRL1, data);
> +	}
> +
> +	st->min_conversions = NAU7802_DEFAULT_CONVERSIONS;
> +
> +	/*
> +	 * The ADC fires continuously and we can't do anything about
> +	 * it. So we need to have the IRQ disabled by default, and we
> +	 * will enable them back when we will need them..
> +	 */
> +	if (client->irq) {
> +		ret = request_threaded_irq(client->irq,
> +				NULL,
> +				nau7802_eoc_trigger,
> +				IRQF_TRIGGER_HIGH | IRQF_ONESHOT,
> +				client->dev.driver->name,
> +				indio_dev);
> +		if (ret) {
> +			/*
> +			 * What may happen here is that our IRQ controller is
> +			 * not able to get level interrupt but this is required
> +			 * by this ADC as when going over 40 sample per second,
> +			 * the interrupt line may stay high between conversions.
> +			 * So, we continue no matter what but we switch to
> +			 * polling mode.
> +			 */
> +			dev_info(&client->dev,
> +				"Failed to allocate IRQ, using polling mode\n");
> +			client->irq = 0;
> +		} else
> +			disable_irq(client->irq);
> +	}
> +
> +	if (!client->irq) {
> +		/*
> +		 * We are polling, use the fastest sample rate by
> +		 * default
> +		 */
> +		st->sample_rate = NAU7802_SAMP_FREQ_320;
> +		i2c_smbus_write_byte_data(st->client, NAU7802_REG_CTRL2,
> +					  NAU7802_CTRL2_CRS(st->sample_rate));
> +	}
> +
> +	/* Setup the ADC channels available on the board */
> +	indio_dev->num_channels = 2;
> +	indio_dev->channels = nau7802_chan_array;
> +
> +	init_completion(&st->value_ok);
> +	mutex_init(&st->lock);
> +	mutex_init(&st->data_lock);
> +
> +	ret = iio_device_register(indio_dev);
> +	if (ret < 0) {
> +		dev_err(&client->dev, "Couldn't register the device.\n");
> +		goto error_device_register;
> +	}
> +
> +	return 0;
> +
> +error_device_register:
> +	mutex_destroy(&st->lock);
> +	mutex_destroy(&st->data_lock);
> +	if (client->irq)
> +		free_irq(client->irq, indio_dev);
> +	iio_device_free(indio_dev);
> +
> +	return ret;
> +}
> +
> +static int nau7802_remove(struct i2c_client *client)
> +{
> +	struct iio_dev *indio_dev = i2c_get_clientdata(client);
> +	struct nau7802_state *st = iio_priv(indio_dev);
> +
> +	iio_device_unregister(indio_dev);
> +	mutex_destroy(&st->lock);
> +	mutex_destroy(&st->data_lock);
> +	if (client->irq)
> +		free_irq(client->irq, indio_dev);
> +	iio_device_free(indio_dev);
> +
> +	return 0;
> +}
> +
> +static const struct i2c_device_id nau7802_i2c_id[] = {
> +	{ "nau7802", 0 },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(i2c, nau7802_i2c_id);
> +
> +static const struct of_device_id nau7802_dt_ids[] = {
> +	{ .compatible = "nuvoton,nau7802" },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, nau7802_dt_ids);
> +
> +static struct i2c_driver nau7802_driver = {
> +	.probe = nau7802_probe,
> +	.remove = nau7802_remove,
> +	.id_table = nau7802_i2c_id,
> +	.driver = {
> +		   .name = "nau7802",
> +		   .of_match_table = of_match_ptr(nau7802_dt_ids),
> +	},
> +};
> +
> +module_i2c_driver(nau7802_driver);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("Nuvoton NAU7802 ADC Driver");
> +MODULE_AUTHOR("Maxime Ripard <maxime.ripard@...e-electrons.com>");
> +MODULE_AUTHOR("Alexandre Belloni <alexandre.belloni@...e-electrons.com>");
>
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