Re: [PATCH] IIO: add si701x driver

[David Barksdale <dbarksdale@uplogix.com>]

On 09/18/2014 12:43 PM, Peter Meerwald wrote:
>
>> This patch adds support to the Industrial IO subsystem
>> for the Silicon Labs Si701x/2x Relative Humidity and
>> Temperature Sensors.
>
> the name si701x is problematic; the si7015 for example is supported by
> the si7005 driver
>
> how about calling the driver si7020 and stating that it also supports
> si7013, si7021 -- the x notation in driver names always leads to touble...

Sounds good.

> the additional features of the si7013 are not supported by the driver
>
>> 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@uplogix.com>
>>
>> ---
>>   drivers/iio/humidity/Kconfig  |  10 +++
>>   drivers/iio/humidity/Makefile |   1 +
>>   drivers/iio/humidity/si701x.c | 159 ++++++++++++++++++++++++++++++++++++++++++
>>   3 files changed, 170 insertions(+)
>>
>> diff --git a/drivers/iio/humidity/Kconfig b/drivers/iio/humidity/Kconfig
>> index e116bd8..ba0ef61 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 SI701X
>> +	tristate "Si701x/2x Relative Humidity and Temperature Sensors"
>> +	depends on I2C
>> +	help
>> +	  Say yes here to build support for the Silicon Labs Si701x/2x Relative
>> +	  Humidity and Temperature Sensors.
>> +
>> +	  To compile this driver as a module, choose M here: the module
>> +	  will be called si701x.
>> +
>>   endmenu
>> diff --git a/drivers/iio/humidity/Makefile b/drivers/iio/humidity/Makefile
>> index e3f3d94..d2e9645 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_SI701X) += si701x.o
>> diff --git a/drivers/iio/humidity/si701x.c b/drivers/iio/humidity/si701x.c
>> new file mode 100644
>> index 0000000..1a2ee22
>> --- /dev/null
>> +++ b/drivers/iio/humidity/si701x.c
>> @@ -0,0 +1,159 @@
>> +/*
>> + * si701x.c - Silicon Labs Si701x/2x Relative Humidity and Temperature Sensors
>> + * Copyright (c) 2013,2014  Uplogix, Inc.
>> + * David Barksdale <dbarksdale@uplogix.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 Si701x/2x 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 */
>> +	SI701XCMD_RH_HOLD	= 0xE5,
>> +	/* Measure Temperature, Hold Master Mode */
>> +	SI701XCMD_TEMP_HOLD	= 0xE3,
>> +};
>> +
>> +struct si701x_data {
>> +	struct i2c_client *client;
>> +	struct mutex lock;
>> +};
>> +
>> +static int si701x_read_raw(struct iio_dev *indio_dev,
>> +			   struct iio_chan_spec const *chan, int *val,
>> +			   int *val2, long mask)
>> +{
>> +	struct si701x_data *data = iio_priv(indio_dev);
>> +	int ret;
>> +
>> +	switch (mask) {
>> +	case IIO_CHAN_INFO_RAW:
>> +		mutex_lock(&data->lock);
>
> is the locking needed? what is protected?

I copied this from the si7005 driver. I assumed because calls to 
read_raw were not serialized and calls to i2c_smbus_read_word_data on 
the same client need to be serialized.

>> +		ret = i2c_smbus_read_word_data(data->client,
>> +					       chan->type == IIO_TEMP ?
>> +					       SI701XCMD_TEMP_HOLD :
>> +					       SI701XCMD_RH_HOLD);
>> +		mutex_unlock(&data->lock);
>> +		if (ret < 0)
>> +			return ret;
>> +		*val = ret;
>> +		return IIO_VAL_INT;
>> +	case IIO_CHAN_INFO_SCALE:
>> +		if (chan->type == IIO_TEMP) {
>> +			*val = 175.72 * 1000;
>
> floating-point constants in kernel space makes me nervous
>

I was trying to make this easy to compare to constants that appear in 
the data sheets: 175.72, 125, 65536, -6, and -46.85. I figured the 
compiler would transform them to integers, but I suppose that's not a 
great assumption. I'll precompute them and explain them in a comment.

>> +			*val2 = 65536;
>
> could set val2 once after the if
>
>> +		} else {
>> +			*val = 125 * 1000;
>> +			*val2 = 65536;
>> +		}
>> +		return IIO_VAL_FRACTIONAL;
>> +	case IIO_CHAN_INFO_OFFSET:
>> +		if (chan->type == IIO_TEMP)
>> +			*val = -46.85 * 65536 / 175.72;
>> +		else
>> +			*val = -6 * 65536 / 125;
>> +		return IIO_VAL_INT;
>> +	default:
>> +		break;
>> +	}
>> +
>> +	return -EINVAL;
>> +}
>> +
>> +static const struct iio_chan_spec si701x_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 si701x_info = {
>> +	.read_raw = si701x_read_raw,
>> +	.driver_module = THIS_MODULE,
>> +};
>> +
>> +static int si701x_probe(struct i2c_client *client,
>> +			const struct i2c_device_id *id)
>> +{
>> +	struct iio_dev *dev;
>> +	struct si701x_data *data;
>> +
>> +	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_WORD_DATA))
>> +		return -ENODEV;
>> +
>> +	dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
>> +	if (!dev)
>> +		return -ENOMEM;
>> +
>> +	data = iio_priv(dev);
>> +	i2c_set_clientdata(client, dev);
>> +	data->client = client;
>> +	mutex_init(&data->lock);
>> +
>> +	dev->dev.parent = &client->dev;
>> +	dev->name = dev_name(&client->dev);
>> +	dev->modes = INDIO_DIRECT_MODE;
>> +	dev->info = &si701x_info;
>> +	dev->channels = si701x_channels;
>> +	dev->num_channels = ARRAY_SIZE(si701x_channels);
>> +
>> +	return devm_iio_device_register(&client->dev, dev);
>> +}
>> +
>> +static const unsigned short si701x_address_list[] = {
>> +	0x40,
>
> the alternate address is 0x41
>

Thanks.

>> +	I2C_CLIENT_END
>> +};
>> +
>> +static const struct i2c_device_id si701x_id[] = {
>> +	{ "si701x", 0 },
>> +	{ }
>> +};
>> +MODULE_DEVICE_TABLE(i2c, si701x_id);
>> +
>> +static struct i2c_driver si701x_driver = {
>> +	.class		= I2C_CLASS_HWMON,
>> +	.driver.name	= "si701x",
>> +	.probe		= si701x_probe,
>> +	.address_list	= si701x_address_list,
>> +	.id_table	= si701x_id,
>
> address_list and I2C_CLASS_HWMON -- what for?
>
> if doing auto-probing, I'd check the chip's ID
>

Oops. This was originally an hwmon driver but I ported it to iio when I 
saw that's where si7005 landed.

>> +};
>> +
>> +module_i2c_driver(si701x_driver);
>> +MODULE_DESCRIPTION("Silicon Labs Si701x/2x "
>> +		   "Relative Humidity and Temperature Sensors");
>> +MODULE_AUTHOR("David Barksdale <dbarksdale@uplogix.com>");
>> +MODULE_LICENSE("GPL");
>> +
>>
>