Re: [PATCH v2] IIO: add si7020 driver

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David Barksdale schrieb, Am 22.09.2014 17:40:
> 
> 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@xxxxxxxxxxx>
>>>
>> 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?
It would be a bit more accurate using a fractional offset, but this error is just in the range of 10 m°C or 4 m%RH. Compared to the tolerances of the sensor for temperature (at least 500 m°C) or humidity (at least 3000 m%RH), this doesn't seem relevant.
> 
>>> --
>>> 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@xxxxxxxxxxx>
>>> + *
>>> + * 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@xxxxxxxxxxx>");
>>> +MODULE_LICENSE("GPL");
>>> +
>>>
>>
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