Subject: Re: [PATCH 2/2] iio: adc: Add driver for the TI ADS8344 A/DC chips

From: Jonathan Cameron <[email-masked]>
Date: Sat, 16 Mar 2019 17:06:30 +0000

On Fri, 15 Mar 2019 16:11:51 +0100
Gregory CLEMENT <[email-masked]> wrote:

> This adds support for the Texas Instruments ADS8344 ADC chip. This chip
> has a 16-bit 8-Channel ADC and is access directly through SPI.
> 
> Signed-off-by: Gregory CLEMENT <[email-masked]>

Hi Gregory,

A few minor bits and pieces inline. Some of them due I would guess to
cut and paste from a driver where things were slightly different!

If we were late in the cycle this lot would probably have been
small enough that I'd just have reworked it whilst applying, but
we are really early, hence you get to tidy them up ;)

Thanks,

Jonathan

> ---
>  drivers/iio/adc/Kconfig      |  10 ++
>  drivers/iio/adc/Makefile     |   1 +
>  drivers/iio/adc/ti-ads8344.c | 216 +++++++++++++++++++++++++++++++++++
>  3 files changed, 227 insertions(+)
>  create mode 100644 drivers/iio/adc/ti-ads8344.c
> 
> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> index 76db6e5cc296..447d3a871746 100644
> --- a/drivers/iio/adc/Kconfig
> +++ b/drivers/iio/adc/Kconfig
> @@ -967,6 +967,16 @@ config TI_ADS7950
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called ti-ads7950.
>  
> +config TI_ADS8344
> +	tristate "Texas Instruments ADS8344"
> +	depends on SPI && OF
> +	help
> +	  If you say yes here you get support for Texas Instruments ADS8344
> +	  ADC chips
> +
> +	  This driver can also be built as a module. If so, the module will be
> +	  called ti-ads8344.
> +
>  config TI_ADS8688
>  	tristate "Texas Instruments ADS8688"
>  	depends on SPI && OF
> diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
> index 6fcebd167524..1f3ae934111d 100644
> --- a/drivers/iio/adc/Makefile
> +++ b/drivers/iio/adc/Makefile
> @@ -87,6 +87,7 @@ obj-$(CONFIG_TI_ADC128S052) += ti-adc128s052.o
>  obj-$(CONFIG_TI_ADC161S626) += ti-adc161s626.o
>  obj-$(CONFIG_TI_ADS1015) += ti-ads1015.o
>  obj-$(CONFIG_TI_ADS7950) += ti-ads7950.o
> +obj-$(CONFIG_TI_ADS8344) += ti-ads8344.o
>  obj-$(CONFIG_TI_ADS8688) += ti-ads8688.o
>  obj-$(CONFIG_TI_ADS124S08) += ti-ads124s08.o
>  obj-$(CONFIG_TI_AM335X_ADC) += ti_am335x_adc.o
> diff --git a/drivers/iio/adc/ti-ads8344.c b/drivers/iio/adc/ti-ads8344.c
> new file mode 100644
> index 000000000000..6159d8518871
> --- /dev/null
> +++ b/drivers/iio/adc/ti-ads8344.c
> @@ -0,0 +1,216 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * ADS8344 16-bit 8-Channel ADC driver
> + *
> + * Author: Gregory CLEMENT <[email-masked]>
> + *
> + * Datasheet: http://www.ti.com/lit/ds/symlink/ads8344.pdf
> + */
> +
> +#include <linux/delay.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/iio.h>
> +#include <linux/module.h>
> +#include <linux/regulator/consumer.h>
> +#include <linux/spi/spi.h>
> +
> +struct ads8344 {
> +	struct spi_device *spi;
> +	struct regulator *reg;
> +	struct mutex lock;
> +
> +	u8 tx_buf ____cacheline_aligned;
> +	u16 rx_buf;
> +};
> +
> +#define ADS8344_VOLTAGE_CHANNEL(chan, si)				\
> +	{								\
> +		.type = IIO_VOLTAGE,					\
> +		.indexed = 1,						\
> +		.channel = chan,					\
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
> +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
> +		.scan_index = si,					\
> +		.scan_type = {						\

You aren't currently providing a buffer, so please drop scan_index and
scan_type until you are.  The code won't do anything with them at the moment.

> +			.sign = 'u',					\
> +			.realbits = 16,					\
> +			.storagebits = 16,				\
> +		},							\
> +	}
> +
> +#define ADS8344_VOLTAGE_CHANNEL_DIFF(chan1, chan2, si)			\
> +	{								\
> +		.type = IIO_VOLTAGE,					\
> +		.indexed = 1,						\
> +		.channel = (chan1),					\
> +		.channel2 = (chan2),					\
> +		.differential = 1,					\
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
> +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
> +		.scan_index = si,					\
> +		.scan_type = {						\
> +			.sign = 'u',					\
> +			.realbits = 16,					\
> +			.storagebits = 16,				\
> +		},							\
> +	}
> +
> +static const struct iio_chan_spec ads8344_channels[] = {
> +	ADS8344_VOLTAGE_CHANNEL(0, 0),
> +	ADS8344_VOLTAGE_CHANNEL(1, 4),
> +	ADS8344_VOLTAGE_CHANNEL(2, 1),
> +	ADS8344_VOLTAGE_CHANNEL(3, 5),
> +	ADS8344_VOLTAGE_CHANNEL(4, 2),
> +	ADS8344_VOLTAGE_CHANNEL(5, 6),
> +	ADS8344_VOLTAGE_CHANNEL(6, 3),
> +	ADS8344_VOLTAGE_CHANNEL(7, 7),
> +	ADS8344_VOLTAGE_CHANNEL_DIFF(0, 1, 8),
> +	ADS8344_VOLTAGE_CHANNEL_DIFF(2, 3, 9),
> +	ADS8344_VOLTAGE_CHANNEL_DIFF(4, 5, 10),
> +	ADS8344_VOLTAGE_CHANNEL_DIFF(6, 7, 11),
> +	ADS8344_VOLTAGE_CHANNEL_DIFF(1, 0, 12),
> +	ADS8344_VOLTAGE_CHANNEL_DIFF(3, 2, 13),
> +	ADS8344_VOLTAGE_CHANNEL_DIFF(5, 4, 14),
> +	ADS8344_VOLTAGE_CHANNEL_DIFF(7, 6, 15),
> +};
> +
> +static int ads8344_adc_conversion(struct ads8344 *adc, int channel,
> +				  bool differential)
> +{
> +	struct spi_device *spi = adc->spi;
> +	int ret;
> +
> +	/* start bit */
> +	adc->tx_buf = BIT(7);
> +	/* single-ended or differential */
> +	adc->tx_buf |= differential ? 0 : BIT(2);
> +	/* select channel(s) */
The moment you need comments to say what a bit is, you are
almost always better off adding some defines so that this
block becomes something like.

adc->tx_buff = ADS8344_START;
if (!differential)
	adc->tx_buff |= ADS8344_SINGLE_END;
adc->tx_buff |= ADS8344_CHANNEL(channel);
adc->tx_buff |= ADS8344_CLOCK_INTERNAL;

Then you can drop the comments and the defines are nice
and easy to check against a datasheet as they are all in
one place.

> +	adc->tx_buf |= channel << 4;
> +	/* internal clock mode */
> +	adc->tx_buf |= 0x2;
> +
> +	ret = spi_write(spi, &adc->tx_buf, 1);
> +	if (ret)
> +		return ret;
> +
> +	udelay(9);
> +
> +	ret = spi_read(spi, &adc->rx_buf, 2);
> +	if (ret)
> +		return ret;
> +
> +	return adc->rx_buf;
> +}
> +
> +static int ads8344_read_raw(struct iio_dev *iio,
> +			    struct iio_chan_spec const *channel, int *value,
> +			    int *shift, long mask)
> +{
> +	struct ads8344 *adc = iio_priv(iio);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		mutex_lock(&adc->lock);
> +		*value = ads8344_adc_conversion(adc, channel->scan_index,
> +						channel->differential);
> +		mutex_unlock(&adc->lock);
> +		if (*value < 0)
> +			return *value;
> +
> +		return IIO_VAL_INT;
> +	case IIO_CHAN_INFO_SCALE:
> +		*value = regulator_get_voltage(adc->reg);
> +		if (*value < 0)
> +			return *value;
> +
> +		/* convert regulator output voltage to mV */
> +		*value /= 1000;
> +		*shift = 16;
> +
> +		return IIO_VAL_FRACTIONAL_LOG2;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static const struct iio_info ads8344_info = {
> +	.read_raw = ads8344_read_raw,
> +};
> +
> +static int ads8344_probe(struct spi_device *spi)
> +{
> +	struct iio_dev *indio_dev;
> +	struct ads8344 *adc;
> +	int ret;
> +
> +	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);
> +
> +	indio_dev->name = dev_name(&spi->dev);
> +	indio_dev->dev.parent = &spi->dev;
> +	indio_dev->dev.of_node = spi->dev.of_node;
> +	indio_dev->info = &ads8344_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->channels = ads8344_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(ads8344_channels);
> +
> +	adc->reg = devm_regulator_get(&spi->dev, "vref");
> +	if (IS_ERR(adc->reg))
> +		return PTR_ERR(adc->reg);
> +
> +	ret = regulator_enable(adc->reg);
> +	if (ret)
> +		return ret;
> +
> +	spi_set_drvdata(spi, indio_dev);
> +
> +	ret = iio_device_register(indio_dev);
> +	if (ret)
> +		goto err_buffer_cleanup;
> +
> +	return 0;
> +err_buffer_cleanup:

That is not a useful or correct label.. Give it a better name!

> +	regulator_disable(adc->reg);
> +
> +	return ret;
> +}
> +
> +static int ads8344_remove(struct spi_device *spi)
> +{
> +	struct iio_dev *indio_dev = spi_get_drvdata(spi);
> +	struct ads8344 *adc = iio_priv(indio_dev);
> +
> +	iio_device_unregister(indio_dev);
> +	regulator_disable(adc->reg);
> +
> +	return 0;
> +}
> +
> +#ifdef CONFIG_OF

Given there isn't currently any other way of (normally
at least) instantiating this I wouldn't bother with the config guards.
Also see below for additional comment on this.

> +
> +static const struct of_device_id ads8344_dt_ids[] = {
> +	{ .compatible = "ti,ads8344", },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, ads8344_dt_ids);
> +
> +#endif
> +
> +static struct spi_driver ads8344_driver = {
> +	.driver = {
> +		.name = "ads8344",
> +		.of_match_table = of_match_ptr(ads8344_dt_ids),

Don't use of_match_ptr as it breaks the magic ACPI binding which
uses the DT tables.

> +	},
> +	.probe = ads8344_probe,
> +	.remove = ads8344_remove,
> +};
> +module_spi_driver(ads8344_driver);
> +
> +MODULE_AUTHOR("Gregory CLEMENT <[email-masked]>");
> +MODULE_DESCRIPTION("ADS8344 driver");
> +MODULE_LICENSE("GPL v2");

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