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Date:	Mon, 22 Sep 2014 10:40:09 -0500
From:	David Barksdale <dbarksdale@...ogix.com>
To:	Hartmut Knaack <knaack.h@....de>,
	Jonathan Cameron <jic23@...nel.org>
CC:	Peter Meerwald <pmeerw@...erw.net>, <linux-kernel@...r.kernel.org>,
	<linux-iio@...r.kernel.org>
Subject: Re: [PATCH v2] IIO: add si7020 driver


On 09/21/2014 07:27 AM, Hartmut Knaack wrote:
> David Barksdale schrieb, Am 18.09.2014 22:01:
>> This patch adds support to the Industrial IO subsystem
>> for the Silicon Labs Si7013/20/21 Relative Humidity and
>> Temperature Sensors.
>>
>> Website: http://www.silabs.com/products/sensors/humidity-sensors/Pages/si7013-20-21.aspx
>>
>> These are i2c devices which measure relative humidity
>> and temperature and all use the same protocol. The
>> Si7013 has an additional input with programmable
>> linearization which is not supported because that's
>> complicated and I didn't need it.
>>
>> Signed-off-by: David Barksdale <dbarksdale@...ogix.com>
>>
> Hi,
> I'm not really convinced of the concept of treating all measurements as 16 bit data, since the datasheet states a maximum resolution of 14 bits for temperature and 12 bits for humidity. It also states, that the 2 LSBs contain an identifier rather than measured data. So, the least to do would be to mask out everything, which is not measured data (which should also include the 2 MSBs of humidity channel). Even better would be to also apply a shift and treat the data with the real resolution (especially for scale, as it would represent the sensitivity of the sensor a bit better).
> Besides that, I think it would be a good idea to initialize the sensor during probe (for example set resolution to maximum), since you can never be sure, in which state the sensor has been before.
> Also, find some small style issues inline.

The math done by iio_convert_raw_to_processed_unlocked loses accuracy in 
my case because I need the offset to be fractional. It assumes offset is 
an integer so I have to round the true offset to the nearest integer.
If I provide IIO_CHAN_INFO_PROCESSED then I can do the math correctly.
Would it be kosher to provide only IIO_CHAN_INFO_RAW and 
IIO_CHAN_INFO_PROCESSED?

>> --
>> Changes since v1:
>> * Renamed to si7020 and replaced Si701x/2x with Si7013/20/21.
>> * Removed unneeded mutex.
>> * Pre-computed floating-point constant expressions.
>> * Removed address_list and I2C_CLASS_HWMON.
>>
>> ---
>>   drivers/iio/humidity/Kconfig  |  10 +++
>>   drivers/iio/humidity/Makefile |   1 +
>>   drivers/iio/humidity/si7020.c | 142 ++++++++++++++++++++++++++++++++++++++++++
>>   3 files changed, 153 insertions(+)
>>
>> diff --git a/drivers/iio/humidity/Kconfig b/drivers/iio/humidity/Kconfig
>> index e116bd8..4813b79 100644
>> --- a/drivers/iio/humidity/Kconfig
>> +++ b/drivers/iio/humidity/Kconfig
>> @@ -22,4 +22,14 @@ config SI7005
>>   	  To compile this driver as a module, choose M here: the module
>>   	  will be called si7005.
>>
>> +config SI7020
>> +	tristate "Si7013/20/21 Relative Humidity and Temperature Sensors"
>> +	depends on I2C
>> +	help
>> +	  Say yes here to build support for the Silicon Labs Si7013/20/21
>> +	  Relative Humidity and Temperature Sensors.
>> +
>> +	  To compile this driver as a module, choose M here: the module
>> +	  will be called si7020.
>> +
>>   endmenu
>> diff --git a/drivers/iio/humidity/Makefile b/drivers/iio/humidity/Makefile
>> index e3f3d94..86e2d26 100644
>> --- a/drivers/iio/humidity/Makefile
>> +++ b/drivers/iio/humidity/Makefile
>> @@ -4,3 +4,4 @@
>>
>>   obj-$(CONFIG_DHT11) += dht11.o
>>   obj-$(CONFIG_SI7005) += si7005.o
>> +obj-$(CONFIG_SI7020) += si7020.o
>> diff --git a/drivers/iio/humidity/si7020.c b/drivers/iio/humidity/si7020.c
>> new file mode 100644
>> index 0000000..cabdb7d
>> --- /dev/null
>> +++ b/drivers/iio/humidity/si7020.c
>> @@ -0,0 +1,142 @@
>> +/*
>> + * si7020.c - Silicon Labs Si7013/20/21 Relative Humidity and Temp Sensors
>> + * Copyright (c) 2013,2014  Uplogix, Inc.
>> + * David Barksdale <dbarksdale@...ogix.com>
>> + *
>> + * This program is free software; you can redistribute it and/or modify it
>> + * under the terms and conditions of the GNU General Public License,
>> + * version 2, as published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> + * GNU General Public License for more details.
>> + */
>> +
>> +/*
>> + * The Silicon Labs Si7013/20/21 Relative Humidity and Temperature Sensors
>> + * are i2c devices which have an identical programming interface for
>> + * measuring relative humidity and temperature. The Si7013 has an additional
>> + * temperature input which this driver does not support.
>> + *
>> + * Data Sheets:
>> + *   Si7013: http://www.silabs.com/Support%20Documents/TechnicalDocs/Si7013.pdf
>> + *   Si7020: http://www.silabs.com/Support%20Documents/TechnicalDocs/Si7020.pdf
>> + *   Si7021: http://www.silabs.com/Support%20Documents/TechnicalDocs/Si7021.pdf
>> + */
>> +
>> +#include <linux/i2c.h>
>> +#include <linux/module.h>
>> +#include <linux/slab.h>
>> +#include <linux/sysfs.h>
>> +
>> +#include <linux/iio/iio.h>
>> +#include <linux/iio/sysfs.h>
>> +
>> +enum {
>> +	/* Measure Relative Humidity, Hold Master Mode */
>> +	SI7020CMD_RH_HOLD	= 0xE5,
>> +	/* Measure Temperature, Hold Master Mode */
>> +	SI7020CMD_TEMP_HOLD	= 0xE3,
>> +};
>> +
>> +static int si7020_read_raw(struct iio_dev *indio_dev,
>> +			   struct iio_chan_spec const *chan, int *val,
>> +			   int *val2, long mask)
>> +{
>> +	struct i2c_client **client = iio_priv(indio_dev);
>> +	int ret;
>> +
>> +	switch (mask) {
>> +	case IIO_CHAN_INFO_RAW:
>> +		ret = i2c_smbus_read_word_data(*client,
>> +					       chan->type == IIO_TEMP ?
>> +					       SI7020CMD_TEMP_HOLD :
>> +					       SI7020CMD_RH_HOLD);
>> +		if (ret < 0)
>> +			return ret;
>> +		*val = ret;
>> +		return IIO_VAL_INT;
>> +	case IIO_CHAN_INFO_SCALE:
>> +		if (chan->type == IIO_TEMP)
>> +			*val = 175720; /* = 175.72 * 1000 */
>> +		else
>> +			*val = 125 * 1000;
>> +		*val2 = 65536;
>> +		return IIO_VAL_FRACTIONAL;
>> +	case IIO_CHAN_INFO_OFFSET:
>> +		if (chan->type == IIO_TEMP)
>> +			*val = -17473; /* = -46.85 * 65536 / 175.72 */
>> +		else
>> +			*val = -3146; /* = -6 * 65536 / 125 */
>> +		return IIO_VAL_INT;
>> +	default:
>> +		break;
>> +	}
>> +
>> +	return -EINVAL;
>> +}
>> +
>> +static const struct iio_chan_spec si7020_channels[] = {
>> +	{
>> +		.type = IIO_HUMIDITYRELATIVE,
>> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
>> +			BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET),
>> +	},
>> +	{
>> +		.type = IIO_TEMP,
>> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
>> +			BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET),
>> +	}
>> +};
>> +
>> +static const struct iio_info si7020_info = {
>> +	.read_raw = si7020_read_raw,
>> +	.driver_module = THIS_MODULE,
>> +};
>> +
>> +static int si7020_probe(struct i2c_client *client,
>> +			const struct i2c_device_id *id)
>> +{
>> +	struct iio_dev *dev;
> Better name it indio_dev.
>> +	struct i2c_client **data;
>> +
>> +	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_WORD_DATA))
>> +		return -ENODEV;
>> +
>> +	dev = devm_iio_device_alloc(&client->dev, sizeof(*client));
>> +	if (!dev)
>> +		return -ENOMEM;
>> +
>> +	data = iio_priv(dev);
>> +	*data = client;
>> +	i2c_set_clientdata(client, dev);
>> +
>> +	dev->dev.parent = &client->dev;
>> +	dev->name = dev_name(&client->dev);
>> +	dev->modes = INDIO_DIRECT_MODE;
>> +	dev->info = &si7020_info;
>> +	dev->channels = si7020_channels;
>> +	dev->num_channels = ARRAY_SIZE(si7020_channels);
>> +
>> +	return devm_iio_device_register(&client->dev, dev);
>> +}
>> +
>> +static const struct i2c_device_id si7020_id[] = {
>> +	{ "si7020", 0 },
>> +	{ }
>> +};
>> +MODULE_DEVICE_TABLE(i2c, si7020_id);
>> +
>> +static struct i2c_driver si7020_driver = {
>> +	.driver.name	= "si7020",
>> +	.probe		= si7020_probe,
>> +	.id_table	= si7020_id,
>> +};
>> +
>> +module_i2c_driver(si7020_driver);
>> +MODULE_DESCRIPTION("Silicon Labs Si7013/20/21 "
> Trailing whitespace in string.
>> +		   "Relative Humidity and Temperature Sensors");
>> +MODULE_AUTHOR("David Barksdale <dbarksdale@...ogix.com>");
>> +MODULE_LICENSE("GPL");
>> +
>>
>
--
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