Re: [PATCH v4 2/2] iio: adc: Add MAX1241 driver

[Jonathan Cameron <jic23@kernel.org>]

On Fri, 20 Mar 2020 17:01:15 +0200
Alexandru Lazar <alazar@startmail.com> wrote:

> Add driver for the Maxim MAX1241 12-bit, single-channel ADC. The driver
> includes support for this device's low-power operation mode.
> 
> Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> Signed-off-by: Alexandru Lazar <alazar@startmail.com>

Few minor things inline, but looks good in general.

> ---
>  drivers/iio/adc/Kconfig   |  10 ++
>  drivers/iio/adc/Makefile  |   1 +
>  drivers/iio/adc/max1241.c | 206 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 217 insertions(+)
>  create mode 100644 drivers/iio/adc/max1241.c
> 
> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> index 5d8540b7b427..55f6462cd93f 100644
> --- a/drivers/iio/adc/Kconfig
> +++ b/drivers/iio/adc/Kconfig
> @@ -566,6 +566,16 @@ config MAX1118
>  	  To compile this driver as a module, choose M here: the module will be
>  	  called max1118.
>  
> +config MAX1241
> +	tristate "Maxim max1241 ADC driver"
> +	depends on SPI_MASTER
> +	help
> +	  Say yes here to build support for Maxim max1241 12-bit, single-channel
> +	  ADC.
> +
> +	  To compile this driver as a module, choose M here: the module will be
> +	  called max1241.
> +
>  config MAX1363
>  	tristate "Maxim max1363 ADC driver"
>  	depends on I2C
> diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
> index a1f1fbec0f87..37d6f17559dc 100644
> --- a/drivers/iio/adc/Makefile
> +++ b/drivers/iio/adc/Makefile
> @@ -54,6 +54,7 @@ obj-$(CONFIG_LTC2497) += ltc2497.o
>  obj-$(CONFIG_MAX1027) += max1027.o
>  obj-$(CONFIG_MAX11100) += max11100.o
>  obj-$(CONFIG_MAX1118) += max1118.o
> +obj-$(CONFIG_MAX1241) += max1241.o
>  obj-$(CONFIG_MAX1363) += max1363.o
>  obj-$(CONFIG_MAX9611) += max9611.o
>  obj-$(CONFIG_MCP320X) += mcp320x.o
> diff --git a/drivers/iio/adc/max1241.c b/drivers/iio/adc/max1241.c
> new file mode 100644
> index 000000000000..0278510ec346
> --- /dev/null
> +++ b/drivers/iio/adc/max1241.c
> @@ -0,0 +1,206 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * MAX1241 low-power, 12-bit serial ADC
> + *
> + * Datasheet: https://datasheets.maximintegrated.com/en/ds/MAX1240-MAX1241.pdf
> + */
> +
> +#include <linux/regulator/consumer.h>

Nitpick; Tidy up ordering of headers.  If no other reason to have a particular
order go with alphabetical.

> +#include <linux/delay.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/iio/iio.h>
> +#include <linux/module.h>
> +#include <linux/spi/spi.h>
> +
> +#define MAX1241_VAL_MASK 0xFFF
> +#define MAX1241_SHDN_DELAY_USEC 4
> +
> +enum max1241_id {
> +	max1241,
> +};
> +
> +struct max1241 {
> +	struct spi_device *spi;
> +	struct mutex lock;
> +	struct regulator *reg;
> +	struct gpio_desc *shdn;
> +
> +	__be16 data ____cacheline_aligned;
> +};
> +
> +static const struct iio_chan_spec max1241_channels[] = {
> +	{
> +		.type = IIO_VOLTAGE,
> +		.indexed = 1,
> +		.channel = 0,
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
> +				BIT(IIO_CHAN_INFO_SCALE),
> +		.scan_index = 0,
> +		.scan_type = {
> +			.sign = 'u',
> +			.realbits = 12,
> +			.storagebits = 16,
> +		},

No need to specify scan_index or scan_type unless the driver supports
buffered modes.  Nothing will use them until then.

> +	},
> +};
> +
> +static int max1241_read(struct max1241 *adc)
> +{
> +	struct spi_transfer xfers[] = {
> +		/*
> +		 * Begin conversion by bringing /CS low for at least
> +		 * tconv us.
> +		 */
> +		{
> +			.len = 0,
> +			.delay.value = 8,
> +			.delay.unit = SPI_DELAY_UNIT_USECS,
> +		},
> +		/*
> +		 * Then read two bytes of data in our RX buffer.
> +		 */
> +		{
> +			.rx_buf = &adc->data,
> +			.len = 2,
> +		},
> +	};
> +
> +	return spi_sync_transfer(adc->spi, xfers, ARRAY_SIZE(xfers));
> +}
> +
> +static int max1241_read_raw(struct iio_dev *indio_dev,
> +			struct iio_chan_spec const *chan,
> +			int *val, int *val2, long mask)
> +{
> +	int ret, vref_uV;
> +	struct max1241 *adc = iio_priv(indio_dev);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		mutex_lock(&adc->lock);
> +
> +		if (adc->shdn) {
> +			gpiod_set_value(adc->shdn, 0);
> +			udelay(MAX1241_SHDN_DELAY_USEC);
> +		}
> +
> +		ret = max1241_read(adc);
> +
> +		if (adc->shdn)
> +			gpiod_set_value(adc->shdn, 1);
> +
> +		if (ret) {
> +			mutex_unlock(&adc->lock);
> +			return ret;
> +		}
> +
> +		*val = (be16_to_cpu(adc->data) >> 3) & MAX1241_VAL_MASK;
> +
> +		mutex_unlock(&adc->lock);
> +		return IIO_VAL_INT;
> +	case IIO_CHAN_INFO_SCALE:
> +		vref_uV = regulator_get_voltage(adc->reg);
> +
> +		if (vref_uV < 0)
> +			return vref_uV;
> +
> +		*val = vref_uV / 1000;
> +		*val2 = 12;
> +
> +		return IIO_VAL_FRACTIONAL_LOG2;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static const struct iio_info max1241_info = {
> +	.read_raw = max1241_read_raw,
> +};
> +
> +static void max1241_disable_reg_action(void *data)
> +{
> +	struct max1241 *adc = data;
> +	int err;
> +
> +	err = regulator_disable(adc->reg);
> +	if (err)
> +		dev_err(&adc->spi->dev, "could not disable reference regulator.\n");
> +}
> +
> +static int max1241_probe(struct spi_device *spi)
> +{
> +	struct iio_dev *indio_dev;
> +	struct max1241 *adc;
> +	int ret = 0;

Looks like ret is always set in all the paths that can use it.
Hence no need to initialize here.

> +
> +	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*adc));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	adc = iio_priv(indio_dev);
> +	adc->spi = spi;
> +	mutex_init(&adc->lock);
> +
> +	spi_set_drvdata(spi, indio_dev);
> +
> +	adc->reg = devm_regulator_get(&spi->dev, "vref");
> +	if (IS_ERR(adc->reg)) {
> +		dev_err(&spi->dev, "failed to get vref regulator\n");
> +		return PTR_ERR(adc->reg);
> +	}
> +
> +	ret = regulator_enable(adc->reg);
> +	if (ret)
> +		return ret;
> +
> +	ret = devm_add_action_or_reset(&spi->dev, max1241_disable_reg_action,
> +					adc);
> +	if (ret) {
> +		dev_err(&spi->dev, "could not set up regulator cleanup action!\n");
> +		return ret;
> +	}
> +
> +	adc->shdn = devm_gpiod_get_optional(&spi->dev, "shdn", GPIOD_OUT_HIGH);
> +
> +	if (IS_ERR(adc->shdn))
> +		return PTR_ERR(adc->shdn);
> +
> +	if (!adc->shdn)
> +		dev_dbg(&spi->dev, "no shdn pin passed, low-power mode disabled");
> +	else
> +		dev_dbg(&spi->dev, "shdn pin passed, low-power mode enabled");
> +
> +	indio_dev->name = spi_get_device_id(spi)->name;
> +	indio_dev->dev.parent = &spi->dev;
> +	indio_dev->info = &max1241_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->channels = max1241_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(max1241_channels);
> +
> +	return devm_iio_device_register(&spi->dev, indio_dev);
> +}
> +
> +static const struct spi_device_id max1241_id[] = {
> +	{ "max1241", max1241 },
> +	{},
> +};
> +
> +static const struct of_device_id max1241_dt_ids[] = {
> +	{ .compatible = "maxim,max1241" },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, max1241_dt_ids);
> +
> +static struct spi_driver max1241_spi_driver = {
> +	.driver = {
> +		.name = "max1241",
> +		.of_match_table = max1241_dt_ids,
> +	},
> +	.probe = max1241_probe,
> +	.id_table = max1241_id,
> +};
> +module_spi_driver(max1241_spi_driver);
> +
> +MODULE_AUTHOR("Alexandru Lazar <alazar@startmail.com>");
> +MODULE_DESCRIPTION("MAX1241 ADC driver");
> +MODULE_LICENSE("GPL v2");