Re: [PATCH v2] iio: adc: ltc2485: add support for Linear Technology LTC2485 ADC

[Jonathan Cameron]

On 25/08/16 06:48, Alison Schofield wrote:
> Adds basic support for the LTC2485 ADC - a delta-sigma analog-to-digital
> converter with an I2C interface that operates in single shot conversion
> mode.
> 
> The driver supports an on board 5V reference and the power-on default
> configuration which rejects both 50hz & 60hz line frequencies and
> operates in 1x speed mode.
> 
> Signed-off-by: Alison Schofield <amsfield22@xxxxxxxxx>
> Cc: Daniel Baluta <daniel.baluta@xxxxxxxxx>
> ---
> Changes in v2:
>   - changed the wait conversion time function to use monotonic rather than
>     real time and to use milliseconds rather than nanoseconds.  
>   - made conv time a constant int.
> 
> Same notes as in v1:
> Reviewers: In addition to commenting on what is present, please comment
> on what is absent and the priority in which you would like to see
> additional features added to this driver, or needed in this first submittal.
None of the below are needed for initially submital.
All 'value' add features at the end of the day. Job one: get reading from
ADC done :)

I made a few really small white space changes and applied this to the
togreg branch of iio.git.  Will be initially pushed out as testing
in a few minutes time to check the autobuilders can't find anything.

Thanks,

Jonathan

> 
> Not supported: 
> 1. External Vref
> 2. Additional Configuration Modes
>         Temperature Sensor Mode: report temp data (not voltage).
> 
>         Line Frequency Rejection Mode: select to reject 50Hz or 60Hz
> 	or both. (both is default)
This is interesting... Will need some new ABI.  It's a filter so we probably
want to try and fit it in with the existing filter ABI.  
> 
>         Speed Mode: Default speed mode (1x) performs two conversions each
> 	cycle and combines the results.  2x speed mode only does one
> 	conversion each cycle.
Really simple case of oversampling.  So this one is easy ;)

> 3. Power management
> 4. DT Bindings
> 5. Triggered buffers
Device is really slow, so no real rush on this one.  Nice to have for
the convenience of using standard interfaces in libiio etc, but
at 7sps reading sysfs will work fine for all usecases!

> 6. What else?
Other power supply regulators..
(allows complete power disabling if there is an appropriate controllable
regulator on the board).

> 
> 
>  drivers/iio/adc/Kconfig   |   9 +++
>  drivers/iio/adc/Makefile  |   1 +
>  drivers/iio/adc/ltc2485.c | 146 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 156 insertions(+)
>  create mode 100644 drivers/iio/adc/ltc2485.c
> 
> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> index 1de31bd..a042611 100644
> --- a/drivers/iio/adc/Kconfig
> +++ b/drivers/iio/adc/Kconfig
> @@ -264,6 +264,15 @@ config LPC18XX_ADC
>  	  To compile this driver as a module, choose M here: the module will be
>  	  called lpc18xx_adc.
>  
> +config LTC2485
> +	tristate "Linear Technology LTC2485 ADC driver"
> +	depends on I2C
> +	help
> +	  Say yes here to build support for Linear Technology LTC2485 ADC.
> +
> +	  To compile this driver as a module, choose M here: the module will be
> +	  called ltc2485.
> +
>  config MAX1027
>  	tristate "Maxim max1027 ADC driver"
>  	depends on SPI
> diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
> index 0ba0d50..1be5747 100644
> --- a/drivers/iio/adc/Makefile
> +++ b/drivers/iio/adc/Makefile
> @@ -27,6 +27,7 @@ obj-$(CONFIG_IMX7D_ADC) += imx7d_adc.o
>  obj-$(CONFIG_INA2XX_ADC) += ina2xx-adc.o
>  obj-$(CONFIG_LP8788_ADC) += lp8788_adc.o
>  obj-$(CONFIG_LPC18XX_ADC) += lpc18xx_adc.o
> +obj-$(CONFIG_LTC2485) += ltc2485.o
>  obj-$(CONFIG_MAX1027) += max1027.o
>  obj-$(CONFIG_MAX1363) += max1363.o
>  obj-$(CONFIG_MCP320X) += mcp320x.o
> diff --git a/drivers/iio/adc/ltc2485.c b/drivers/iio/adc/ltc2485.c
> new file mode 100644
> index 0000000..d8f9dac
> --- /dev/null
> +++ b/drivers/iio/adc/ltc2485.c
> @@ -0,0 +1,146 @@
> +/*
> + * ltc2485.c - Driver for Linear Technology LTC2485 ADC
> + *
> + * Copyright (C) 2016 Alison Schofield <amsfield22@xxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * Datasheet: http://cds.linear.com/docs/en/datasheet/2485fd.pdf
> + */
> +
> +#include <linux/delay.h>
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
> +
> +/* Power-on configuration: rejects both 50/60Hz, operates at 1x speed */
> +#define LTC2485_CONFIG_DEFAULT		0
> +
> +struct ltc2485_data {
> +	struct i2c_client	*client;
> +	ktime_t			time_prev;	/* last conversion */
> +};
> +
> +static void ltc2485_wait_conv(struct ltc2485_data *data)
> +{
> +	const unsigned int conv_time = 147;	/* conversion time ms */
> +	unsigned int time_elapsed;
> +
> +	/* delay if conversion time not passed since last read or write */
> +	time_elapsed = ktime_ms_delta(ktime_get(), data->time_prev);
> +
> +	if (time_elapsed < conv_time)
> +		msleep(conv_time - time_elapsed);
> +}
> +
> +static int ltc2485_read(struct ltc2485_data *data, int *val)
> +{
> +	struct i2c_client *client = data->client;
> +	__be32 buf = 0;
> +	int ret;
> +
> +	ltc2485_wait_conv(data);
> +
> +	ret = i2c_master_recv(client, (char *)&buf, 4);
> +	if (ret < 0)  {
> +		dev_err(&client->dev, "i2c_master_recv failed\n");
> +		return ret;
> +	}
> +	data->time_prev = ktime_get();
> +	*val = sign_extend32(be32_to_cpu(buf) >> 6, 24);
Slightly preference for a blank line before a simple return statement like
this.  Makes it ever so slightly easier to read.
> +	return ret;
> +}
> +
> +static int ltc2485_read_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int *val, int *val2, long mask)
> +{
> +	struct ltc2485_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	if (mask == IIO_CHAN_INFO_RAW) {
> +		ret = ltc2485_read(data, val);
> +		if (ret < 0)
> +			return ret;
> +
> +		return IIO_VAL_INT;
> +
> +	} else if (mask == IIO_CHAN_INFO_SCALE) {
> +		*val = 5000;			/* on board vref millivolts */
> +		*val2 = 25;			/* 25 (24 + sign) data bits */
> +		return IIO_VAL_FRACTIONAL_LOG2;
> +
> +	} else {
> +		return -EINVAL;
> +	}
> +}
> +
> +static const struct iio_chan_spec ltc2485_channel[] = {
> +	{
> +		.type = IIO_VOLTAGE,
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE)
> +	},
> +};
> +
> +static const struct iio_info ltc2485_info = {
> +	.read_raw = ltc2485_read_raw,
> +	.driver_module = THIS_MODULE,
> +};
> +
> +static int ltc2485_probe(struct i2c_client *client,
> +			 const struct i2c_device_id *id)
> +{
> +	struct iio_dev *indio_dev;
> +	struct ltc2485_data *data;
> +	int ret;
> +
> +	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C |
> +				     I2C_FUNC_SMBUS_WRITE_BYTE))
> +		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 = &ltc2485_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->channels = ltc2485_channel;
> +	indio_dev->num_channels = ARRAY_SIZE(ltc2485_channel);
> +
> +	ret = i2c_smbus_write_byte(data->client, LTC2485_CONFIG_DEFAULT);
> +	if (ret < 0)
> +		return ret;
> +
> +	data->time_prev = ktime_get();
> +	return devm_iio_device_register(&client->dev, indio_dev);
> +}
> +
> +static const struct i2c_device_id ltc2485_id[] = {
> +	{ "ltc2485", 0 },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(i2c, ltc2485_id);
> +
> +static struct i2c_driver ltc2485_driver = {
> +	.driver = {
> +		.name = "ltc2485",
> +	},
> +	.probe = ltc2485_probe,
> +	.id_table = ltc2485_id,
> +};
> +module_i2c_driver(ltc2485_driver);
> +
> +MODULE_AUTHOR("Alison Schofield <amsfield22@xxxxxxxxx>");
> +MODULE_DESCRIPTION("Linear Technology LTC2485 ADC driver");
> +MODULE_LICENSE("GPL v2");
>