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

From: Gregory CLEMENT <[email-masked]>
Date: Fri, 22 Mar 2019 11:13:27 +0100

Hi Jonathan,
 
 On sam., mars 16 2019, Jonathan Cameron <[email-masked]> wrote:

> 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!

Exactly! :)

>
> 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 ;)

No problem, I agree to have a more polished driver!

>
> 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.

OK

>
>> +			.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.

OK, I agree it looks better.

>
>> +	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!

Actually I am going to remove the goto.

>
>> +	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.

Right and we already have a depend on OF in the Kconfig

> 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.
OK

Thanks,

Gregory

>
>> +	},
>> +	.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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-- 
Gregory Clement, Bootlin
Embedded Linux and Kernel engineering
http://bootlin.com

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