Re: [PATCH v2] IIO: add si7020 driver

From: Hartmut Knaack
Date: Mon Sep 22 2014 - 16:16:15 EST

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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