Re: [PATCH] IIO: add si701x driver

From: David Barksdale
Date: Thu Sep 18 2014 - 14:56:01 EST



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@xxxxxxxxxxx>

---
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@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 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@xxxxxxxxxxx>");
+MODULE_LICENSE("GPL");
+


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