Re: [PATCH] iio: Add LTC2471/LTC2473 driver

[Jonathan Cameron]

On Sun, 2 Jul 2017 10:29:35 +0200 (CEST)
Peter Meerwald-Stadler <pmeerw@xxxxxxxxxx> wrote:

> > The LTC2741 and LTC2473 are single voltage ADC chips. The LTC2473
> > is similar to the LTC2471 but outputs a signed differential value.  
> 
> comments below
>  
> > Datasheet:
> >   http://cds.linear.com/docs/en/datasheet/24713fb.pdf
> > 
> > Signed-off-by: Mike Looijmans <mike.looijmans@xxxxxxxx>
Enough here that I've dropped the patch for now and look forward
to a v2 incorporating both Peter and Lars' comments.

Jonathan
> > ---
> > Note: Moved from "hwmon" subsystem to "iio" as discussed per e-mail,
> > see also: https://patchwork.kernel.org/patch/9816607/
> > Only tested the LTC2741 in real life.
> > 
> >  drivers/iio/adc/Kconfig   |  10 +++
> >  drivers/iio/adc/Makefile  |   1 +
> >  drivers/iio/adc/ltc2471.c | 163 ++++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 174 insertions(+)
> >  create mode 100644 drivers/iio/adc/ltc2471.c
> > 
> > diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> > index 401f47b..fbee44a 100644
> > --- a/drivers/iio/adc/Kconfig
> > +++ b/drivers/iio/adc/Kconfig
> > @@ -362,6 +362,16 @@ config LPC32XX_ADC
> >  	  activate only one via device tree selection.  Provides direct access
> >  	  via sysfs.
> >  
> > +config LTC2471
> > +	tristate "Linear Technology LTC2471 and LTC2473 ADC driver"
> > +	depends on I2C
> > +	help
> > +	  Say yes here to build support for Linear Technology LTC2471 and
> > +	  LTC2473 ADC.
> > +
> > +	  This driver can also be built as a module. If so, the module will
> > +	  be called ltc2471.
> > +
> >  config LTC2485
> >  	tristate "Linear Technology LTC2485 ADC driver"
> >  	depends on I2C
> > diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
> > index 9339bec..afafe85 100644
> > --- a/drivers/iio/adc/Makefile
> > +++ b/drivers/iio/adc/Makefile
> > @@ -34,6 +34,7 @@ obj-$(CONFIG_INA2XX_ADC) += ina2xx-adc.o
> >  obj-$(CONFIG_LP8788_ADC) += lp8788_adc.o
> >  obj-$(CONFIG_LPC18XX_ADC) += lpc18xx_adc.o
> >  obj-$(CONFIG_LPC32XX_ADC) += lpc32xx_adc.o
> > +obj-$(CONFIG_LTC2471) += ltc2471.o
> >  obj-$(CONFIG_LTC2485) += ltc2485.o
> >  obj-$(CONFIG_LTC2497) += ltc2497.o
> >  obj-$(CONFIG_MAX1027) += max1027.o
> > diff --git a/drivers/iio/adc/ltc2471.c b/drivers/iio/adc/ltc2471.c
> > new file mode 100644
> > index 0000000..f26bdad
> > --- /dev/null
> > +++ b/drivers/iio/adc/ltc2471.c
> > @@ -0,0 +1,163 @@
> > +/*
> > + * Driver for Linear Technology LTC2471 and LTC2473 voltage monitors
> > + * The LTC2473 is identical to the 2471, but reports a differential signal.
> > + *
> > + * Copyright (C) 2017 Topic Embedded Products
> > + * Author: Mike Looijmans <mike.looijmans@xxxxxxxx>
> > + *
> > + * License: GPLv2
> > + */
> > +
> > +#include <linux/err.h>
> > +#include <linux/i2c.h>
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/iio/iio.h>
> > +#include <linux/iio/sysfs.h>
> > +
> > +enum chips {  
> 
> ltc2471_ prefix please
> 
> > +	ltc2471,
> > +	ltc2473  
> 
> end last line with a comma, so additions can be done with a one-line patch
> 
> > +};
> > +
> > +struct ltc2471_data {
> > +	struct i2c_client *client;
> > +};
> > +
> > +/* Reference voltage is 1.25V */
> > +#define LTC2471_VREF 1250
> > +
> > +/* Read two bytes from the I2C bus to obtain the ADC result */
> > +static int ltc2471_get_value(struct i2c_client *client)
> > +{
> > +	int ret;
> > +	__be16 buf;
> > +
> > +	ret = i2c_master_recv(client, (char *)&buf, 2);  
> 
> sizeof(buf) probably
> 
> > +	if (ret < 0)
> > +		return ret;
> > +	if (ret != 2)  
> 
> sizeof(buf) probably
> 
> > +		return -EIO;
> > +
> > +	/* MSB first */
> > +	return be16_to_cpu(buf);
> > +}
> > +
> > +static int ltc2471_read_raw(struct iio_dev *indio_dev,
> > +			    struct iio_chan_spec const *chan,
> > +			    int *val, int *val2, long info)
> > +{
> > +	struct ltc2471_data *data = iio_priv(indio_dev);
> > +	int ret;
> > +
> > +	switch (info) {
> > +	case IIO_CHAN_INFO_RAW:
> > +		ret = ltc2471_get_value(data->client);
> > +		if (ret < 0)
> > +			return ret;
> > +		*val = ret;
> > +		return IIO_VAL_INT;
> > +
> > +	case IIO_CHAN_INFO_SCALE:
> > +		if (chan->differential)
> > +			/* Output ranges from -VREF to +VREF */
> > +			*val = 2 * LTC2471_VREF;
> > +		else
> > +			/* Output ranges from 0 to VREF */
> > +			*val = LTC2471_VREF;
> > +		*val2 = 16;	/* 16 data bits */
> > +		return IIO_VAL_FRACTIONAL_LOG2;
> > +
> > +	case IIO_CHAN_INFO_OFFSET:
> > +		if (chan->differential)
> > +			*val = -LTC2471_VREF;
> > +		else
> > +			*val = 0;  
> 
> the non-differential (single ended) chip has no offset channel anyway 
> according to iio_chan_spec...
> 
> > +		return IIO_VAL_INT;
> > +
> > +	default:
> > +		return -EINVAL;
> > +	}
> > +}
> > +
> > +static const struct iio_chan_spec ltc2471_channel[] = {
> > +	{
> > +		.type = IIO_VOLTAGE,
> > +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> > +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
> > +		.differential = 0,  
> 
> .differential = 0 not needed
> 
> > +	},
> > +};
> > +static const struct iio_chan_spec ltc2473_channel[] = {
> > +	{
> > +		.type = IIO_VOLTAGE,
> > +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> > +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |
> > +					    BIT(IIO_CHAN_INFO_OFFSET),
> > +		.differential = 1,
> > +	},
> > +};
> > +
> > +static const struct iio_info ltc2471_info = {
> > +	.read_raw = ltc2471_read_raw,
> > +	.driver_module = THIS_MODULE,
> > +};
> > +
> > +static int ltc2471_i2c_probe(struct i2c_client *client,
> > +			     const struct i2c_device_id *id)
> > +{
> > +	struct iio_dev *indio_dev;
> > +	struct ltc2471_data *data;
> > +	int ret;
> > +
> > +	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
> > +		return -EOPNOTSUPP;
> > +
> > +	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
> > +	if (!indio_dev)
> > +		return -ENOMEM;
> > +
> > +	data = iio_priv(indio_dev);
> > +	i2c_set_clientdata(client, indio_dev);
> > +	data->client = client;
> > +
> > +	indio_dev->dev.parent = &client->dev;
> > +	indio_dev->name = id->name;
> > +	indio_dev->info = &ltc2471_info;
> > +	indio_dev->modes = INDIO_DIRECT_MODE;
> > +	if (id->driver_data == ltc2473)
> > +		indio_dev->channels = ltc2473_channel;
> > +	else
> > +		indio_dev->channels = ltc2471_channel;
> > +	indio_dev->num_channels = 1;
> > +
> > +	/* Trigger once to start conversion and check if chip is there */
> > +	ret = ltc2471_get_value(client);
> > +	if (ret < 0) {
> > +		dev_err(&client->dev, "Cannot read from device.\n");
> > +		return ret;
> > +	}
> > +
> > +	return devm_iio_device_register(&client->dev, indio_dev);
> > +}
> > +
> > +static const struct i2c_device_id ltc2471_i2c_id[] = {
> > +	{ "ltc2471", ltc2471 },
> > +	{ "ltc2473", ltc2473 },
> > +	{}
> > +};
> > +MODULE_DEVICE_TABLE(i2c, ltc2471_i2c_id);
> > +
> > +static struct i2c_driver ltc2471_i2c_driver = {
> > +	.driver = {
> > +		.name = "ltc2471",
> > +	},
> > +	.probe    = ltc2471_i2c_probe,
> > +	.id_table = ltc2471_i2c_id,
> > +};
> > +
> > +module_i2c_driver(ltc2471_i2c_driver);
> > +
> > +MODULE_DESCRIPTION("LTC2471/LTC2473 Sensor Driver");  
> 
> maybe "ADC driver"
> 
> > +MODULE_AUTHOR("Topic Embedded Products");
> > +MODULE_LICENSE("GPL v2");
> >   
>