[PATCH 1/3] iio: humidity: add sht21 relative humidity and temperature sensor driver

[Tomasz Duszynski]

Add sht21 relative humidity and temperature sensor driver. There already
exists an in-kernel driver under hwmon but with limited functionality
like humidity and temperature always measured together at predefined
resolutions, etc.

New iio driver comes without limitations of predecessor, uses non-blocking i2c
communication mode and adds triggered buffer support thus is suited for more
use cases.

Device datasheet can be found under:

https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/ \
Dokumente/2_Humidity_Sensors/Sensirion_Humidity_Sensors_SHT21_Datasheet_V4.pdf

Signed-off-by: Tomasz Duszynski <tduszyns@xxxxxxxxx>
---
 drivers/iio/humidity/Kconfig  |  10 +
 drivers/iio/humidity/Makefile |   1 +
 drivers/iio/humidity/sht21.c  | 519 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 530 insertions(+)
 create mode 100644 drivers/iio/humidity/sht21.c

diff --git a/drivers/iio/humidity/Kconfig b/drivers/iio/humidity/Kconfig
index 866dda133336..93247ecc9324 100644
--- a/drivers/iio/humidity/Kconfig
+++ b/drivers/iio/humidity/Kconfig
@@ -35,6 +35,16 @@ config HTU21
 	  This driver can also be built as a module. If so, the module will
 	  be called htu21.

+config SHT21
+	tristate "Sensirion SHT21 relative humidity and temperature sensor"
+	depends on I2C
+	help
+	  Say yes here to build support for the  Sensirion SHT21 relative
+	  humidity and temperature sensor.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called sht21.
+
 config SI7005
 	tristate "SI7005 relative humidity and temperature sensor"
 	depends on I2C
diff --git a/drivers/iio/humidity/Makefile b/drivers/iio/humidity/Makefile
index c9f089a9a6b8..f2472fd2cc44 100644
--- a/drivers/iio/humidity/Makefile
+++ b/drivers/iio/humidity/Makefile
@@ -5,5 +5,6 @@
 obj-$(CONFIG_DHT11) += dht11.o
 obj-$(CONFIG_HDC100X) += hdc100x.o
 obj-$(CONFIG_HTU21) += htu21.o
+obj-$(CONFIG_SHT21) += sht21.o
 obj-$(CONFIG_SI7005) += si7005.o
 obj-$(CONFIG_SI7020) += si7020.o
diff --git a/drivers/iio/humidity/sht21.c b/drivers/iio/humidity/sht21.c
new file mode 100644
index 000000000000..199933b87297
--- /dev/null
+++ b/drivers/iio/humidity/sht21.c
@@ -0,0 +1,519 @@
+/*
+ * Sensirion SHT21 relative humidity and temperature sensor driver
+ *
+ * Copyright (C) 2017 Tomasz Duszynski <tduszyns@xxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 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.
+ *
+ * 7-bit I2C slave address: 0x40
+ */
+
+#include <linux/bitops.h>
+#include <linux/delay.h>
+#include <linux/i2c.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+#include <linux/iio/trigger_consumer.h>
+#include <linux/iio/triggered_buffer.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/of.h>
+
+#define SHT21_DRV_NAME "sht21"
+
+#define SHT21_TRIGGER_T_MEASUREMENT 0xF3
+#define SHT21_TRIGGER_RH_MEASUREMENT 0xF5
+
+#define SHT21_WRITE_USER_REG 0xE6
+#define SHT21_READ_USER_REG 0xE7
+#define SHT21_SOFT_RESET 0xFE
+
+#define SHT21_USER_REG_RES_8_12 BIT(0)
+#define SHT21_USER_REG_RES_10_13 BIT(7)
+#define SHT21_USER_REG_RES_11_11 (BIT(7) | BIT(0))
+
+#define SHT21_USER_REG_ENABLE_HEATER BIT(2)
+
+enum {
+	RES_12_14,
+	RES_8_12,
+	RES_10_13,
+	RES_11_11,
+};
+
+/*
+ * Combined sampling frequency i.e measuring RH and T together, which seems
+ * to be common case for pressure/humidity sensors, was chosen so that sensor
+ * is active for only 10% of time thus avoiding self-heating effect.
+ *
+ * Note that sampling frequencies are higher when measuring RH or T separately.
+ *
+ * Following table shows how available resolutions, combined sampling frequency
+ * and frequencies for RH and T when measured separately are related.
+ *
+ * +-------------------+-------------+---------+--------+
+ * | RH / T resolution | RH + T [Hz] | RH [Hz] | T [Hz] |
+ * +-------------------+-------------+---------+--------+
+ * | 12 / 14           | 0.88        | 3.45    | 1.18   |
+ * +-------------------+-------------+---------+--------+
+ * | 8 / 12            | 3.85        | 25      | 4.55   |
+ * +-------------------+-------------+---------+--------+
+ * | 10 / 13           | 1.93        | 11.11   | 2.33   |
+ * +-------------------+-------------+---------+--------+
+ * | 11 / 11           | 2.28        | 6.67    | 9.09   |
+ * +-------------------+-------------+---------+--------+
+ */
+static const struct {
+	int freq;
+	int freq2;
+
+	int rh_meas_time;
+	int t_meas_time;
+} sht21_freq_meas_time_tbl[] = {
+	[RES_12_14] = { 0, 880000, 29000, 85000 },
+	[RES_8_12] = { 3, 850000, 4000, 22000 },
+	[RES_10_13] = { 1, 930000, 9000, 43000 },
+	[RES_11_11] = { 2, 280000, 15000, 11000 }
+};
+
+struct sht21_state {
+	struct i2c_client *client;
+	struct mutex lock;
+	int res;
+};
+
+static int sht21_verify_crc(const u8 *data, int len)
+{
+	int i, j;
+	u8 crc = 0;
+
+	for (i = 0; i < len; i++) {
+		crc ^= data[i];
+
+		for (j = 0; j < 8; j++) {
+			if (crc & 0x80)
+				crc = (crc << 1) ^ 0x31;
+			else
+				crc = crc << 1;
+		}
+	}
+
+	return crc == 0;
+}
+
+/* every chunk of data read from sensor has crc byte appended */
+static int sht21_read_data(struct sht21_state *state, int cmd, int *data)
+{
+	int delay, ret = 0;
+	__be32 tmp = 0;
+
+	switch (cmd) {
+	case SHT21_READ_USER_REG:
+		ret = i2c_smbus_read_i2c_block_data(state->client, cmd,
+						    2, (u8 *)&tmp);
+		break;
+	case SHT21_TRIGGER_RH_MEASUREMENT:
+	case SHT21_TRIGGER_T_MEASUREMENT:
+		ret = i2c_smbus_write_byte(state->client, cmd);
+		if (ret)
+			break;
+
+		delay = cmd == SHT21_TRIGGER_RH_MEASUREMENT ?
+			sht21_freq_meas_time_tbl[state->res].rh_meas_time :
+			sht21_freq_meas_time_tbl[state->res].t_meas_time;
+
+		usleep_range(delay, delay + 1000);
+
+		ret = i2c_master_recv(state->client, (u8 *)&tmp, 3);
+		if (ret < 0)
+			break;
+
+		/*
+		 * Sensor should not be active more that 10% of time
+		 * otherwise it heats up and returns biased measurements.
+		 */
+		delay *= 9;
+		usleep_range(delay, delay + 1000);
+
+		break;
+	}
+
+	if (ret < 0)
+		return ret;
+
+	if (!sht21_verify_crc((u8 *)&tmp, ret)) {
+		dev_err(&state->client->dev, "Data integrity check failed\n");
+		return -EINVAL;
+	}
+
+	/* crc byte no longer needed so drop it here */
+	*data = be32_to_cpu(tmp) >> ((sizeof(tmp) - ret + 1) * 8);
+
+	return 0;
+}
+
+static int sht21_write_data(struct sht21_state *state, int cmd, int *data)
+{
+	int ret;
+
+	if (!data)
+		ret = i2c_smbus_write_byte(state->client, cmd);
+	else
+		ret = i2c_smbus_write_byte_data(state->client, cmd, *data);
+
+	return ret;
+}
+
+static int sht21_trigger_measurement(struct sht21_state *state, int cmd, int *data)
+{
+	int ret;
+
+	mutex_lock(&state->lock);
+	ret = sht21_read_data(state, cmd, data);
+	if (ret) {
+		mutex_unlock(&state->lock);
+		return ret;
+	}
+	mutex_unlock(&state->lock);
+
+	return 0;
+}
+
+static int sht21_trigger_rh_measurement(struct sht21_state *state, int *data)
+{
+	int ret = sht21_trigger_measurement(state, SHT21_TRIGGER_RH_MEASUREMENT, data);
+	if (ret)
+		return ret;
+
+	*data >>= 2;
+	*data = (((s64)*data * 125000) >> 14) - 6000;
+
+	return 0;
+}
+
+static int sht21_trigger_t_measurement(struct sht21_state *state, int *data)
+{
+	int ret = sht21_trigger_measurement(state, SHT21_TRIGGER_T_MEASUREMENT, data);
+	if (ret)
+		return ret;
+
+	*data >>= 2;
+	*data = (((s64)*data * 175720) >> 14) - 46850;
+
+	return 0;
+}
+
+static int sht21_set_resolution(struct sht21_state *state, int res)
+{
+	int ret, data;
+
+	ret = sht21_read_data(state, SHT21_READ_USER_REG, &data);
+	if (ret)
+		return ret;
+
+	data &= ~SHT21_USER_REG_RES_11_11;
+
+	switch (res) {
+	case RES_12_14:
+		break;
+	case RES_8_12:
+		data |= SHT21_USER_REG_RES_8_12;
+		break;
+	case RES_10_13:
+		data |= SHT21_USER_REG_RES_10_13;
+		break;
+	case RES_11_11:
+		data |= SHT21_USER_REG_RES_11_11;
+		break;
+	}
+
+	ret = sht21_write_data(state, SHT21_WRITE_USER_REG, &data);
+	if (ret)
+		return ret;
+
+	state->res = res;
+
+	return 0;
+}
+
+static int sht21_soft_reset(struct sht21_state *state)
+{
+	int ret = sht21_write_data(state, SHT21_SOFT_RESET, NULL);
+	if (ret) {
+		dev_err(&state->client->dev, "Failed to reset device\n");
+		return ret;
+	}
+
+	msleep(15);
+
+	return 0;
+}
+
+static irqreturn_t sht21_trigger_handler(int irq, void *p)
+{
+	struct iio_poll_func *pf = p;
+	struct iio_dev *indio_dev = pf->indio_dev;
+	struct sht21_state *state = iio_priv(indio_dev);
+	int buf[4], ret, i, j = 0;
+
+	for_each_set_bit(i, indio_dev->active_scan_mask, indio_dev->masklength) {
+		ret = i == 0 ? sht21_trigger_rh_measurement(state, &buf[j++]) :
+			       sht21_trigger_t_measurement(state, &buf[j++]);
+		if (ret)
+			goto out;
+	}
+
+	iio_push_to_buffers_with_timestamp(indio_dev, buf,
+					   iio_get_time_ns(indio_dev));
+out:
+	iio_trigger_notify_done(indio_dev->trig);
+
+	return IRQ_HANDLED;
+}
+
+static int sht21_read_raw(struct iio_dev *indio_dev,
+			  struct iio_chan_spec const *channel, int *val,
+			  int *val2, long mask)
+{
+	struct sht21_state *state = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_PROCESSED:
+		if (iio_buffer_enabled(indio_dev))
+			return -EBUSY;
+
+		switch (channel->type) {
+		case IIO_HUMIDITYRELATIVE:
+			ret = sht21_trigger_rh_measurement(state, val);
+			if (ret)
+				return ret;
+
+			return IIO_VAL_INT;
+		case IIO_TEMP:
+			ret = sht21_trigger_t_measurement(state, val);
+			if (ret)
+				return ret;
+
+			return IIO_VAL_INT;
+		default:
+			return -EINVAL;
+		}
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		*val = sht21_freq_meas_time_tbl[state->res].freq;
+		*val2 = sht21_freq_meas_time_tbl[state->res].freq2;
+
+		return IIO_VAL_INT_PLUS_MICRO;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int sht21_write_raw(struct iio_dev *indio_dev,
+			   struct iio_chan_spec const *chan,
+			   int val, int val2, long mask)
+{
+	struct sht21_state *state = iio_priv(indio_dev);
+	int i, ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		for (i = 0; i < ARRAY_SIZE(sht21_freq_meas_time_tbl); i++)
+			if (val == sht21_freq_meas_time_tbl[i].freq &&
+			    val2 == sht21_freq_meas_time_tbl[i].freq2)
+				break;
+
+		if (i == ARRAY_SIZE(sht21_freq_meas_time_tbl))
+			return -EINVAL;
+
+		ret = iio_device_claim_direct_mode(indio_dev);
+		if (ret)
+			return ret;
+
+		mutex_lock(&state->lock);
+		ret = sht21_set_resolution(state, i);
+		mutex_unlock(&state->lock);
+
+		iio_device_release_direct_mode(indio_dev);
+
+		return ret;
+	default:
+		return -EINVAL;
+	}
+}
+
+static ssize_t sht21_show_heater(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
+	struct sht21_state *state = iio_priv(indio_dev);
+	int data, ret;
+
+	ret = sht21_read_data(state, SHT21_READ_USER_REG, &data);
+	if (ret)
+		return ret;
+
+	return sprintf(buf, "%d\n", !!(data & SHT21_USER_REG_ENABLE_HEATER));
+}
+
+static ssize_t sht21_write_heater(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t len)
+{
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
+	struct sht21_state *state = iio_priv(indio_dev);
+	int val, data, ret;
+
+	ret = kstrtoint(buf, 10, &val);
+	if (ret)
+		return ret;
+	if (val != 0 && val != 1)
+		return -EINVAL;
+
+	mutex_lock(&state->lock);
+	ret = sht21_read_data(state, SHT21_READ_USER_REG, &data);
+	if (ret) {
+		mutex_unlock(&state->lock);
+		return ret;
+	}
+
+	if (val)
+		data |= SHT21_USER_REG_ENABLE_HEATER;
+	else
+		data &= ~SHT21_USER_REG_ENABLE_HEATER;
+
+	ret = sht21_write_data(state, SHT21_WRITE_USER_REG, &data);
+	mutex_unlock(&state->lock);
+
+	return ret ? ret : len;
+}
+
+static IIO_CONST_ATTR_SAMP_FREQ_AVAIL("0.88 1.93 2.28 3.85");
+static IIO_DEVICE_ATTR(heater_enable, S_IRUGO | S_IWUSR,
+		       sht21_show_heater, sht21_write_heater, 0);
+
+static struct attribute *sht21_attributes[] = {
+	&iio_const_attr_sampling_frequency_available.dev_attr.attr,
+	&iio_dev_attr_heater_enable.dev_attr.attr,
+	NULL
+};
+
+static const struct attribute_group sht21_attribute_group = {
+	.attrs = sht21_attributes,
+};
+
+static const struct iio_info sht21_info = {
+	.driver_module = THIS_MODULE,
+	.read_raw = sht21_read_raw,
+	.write_raw = sht21_write_raw,
+	.attrs = &sht21_attribute_group,
+};
+
+#define SHT21_CHANNEL(_type, _index) { \
+	.type = _type, \
+	.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), \
+	.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ), \
+	.scan_index = _index, \
+	.scan_type = { \
+		.sign = 's', \
+		.realbits = 32, \
+		.storagebits = 32, \
+		.endianness = IIO_CPU, \
+	}, \
+}
+
+static const struct iio_chan_spec sht21_channels[] = {
+	SHT21_CHANNEL(IIO_HUMIDITYRELATIVE, 0),
+	SHT21_CHANNEL(IIO_TEMP, 1),
+	IIO_CHAN_SOFT_TIMESTAMP(2),
+};
+
+static int sht21_probe(struct i2c_client *client, const struct i2c_device_id *id)
+{
+	struct iio_dev *indio_dev;
+	struct sht21_state *data;
+	int ret;
+
+	if (!i2c_check_functionality(client->adapter,
+				     I2C_FUNC_SMBUS_WRITE_BYTE |
+				     I2C_FUNC_SMBUS_BYTE_DATA |
+				     I2C_FUNC_SMBUS_READ_I2C_BLOCK))
+		return -ENODEV;
+
+	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	data = iio_priv(indio_dev);
+	i2c_set_clientdata(client, indio_dev);
+	data->client = client;
+	mutex_init(&data->lock);
+
+	indio_dev->dev.parent = &client->dev;
+	indio_dev->name = id->name;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->info = &sht21_info;
+	indio_dev->channels = sht21_channels;
+	indio_dev->num_channels = ARRAY_SIZE(sht21_channels);
+
+	ret = sht21_soft_reset(data);
+	if (ret)
+		return ret;
+
+	ret = iio_triggered_buffer_setup(indio_dev, NULL,
+					 sht21_trigger_handler, NULL);
+	if (ret)
+		return ret;
+
+	ret = iio_device_register(indio_dev);
+	if (ret)
+		iio_triggered_buffer_cleanup(indio_dev);
+
+	return ret;
+}
+
+static int sht21_remove(struct i2c_client *client)
+{
+	struct iio_dev *indio_dev = i2c_get_clientdata(client);
+
+	iio_device_unregister(indio_dev);
+	iio_triggered_buffer_cleanup(indio_dev);
+
+	return 0;
+}
+
+static const struct i2c_device_id sht21_id[] = {
+	{ "sht21", 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, sht21_id);
+
+static const struct of_device_id sht21_of_match[] = {
+	{ .compatible = "sensirion,sht21" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, sht21_of_match);
+
+static struct i2c_driver sht21_driver = {
+	.driver = {
+		.name = SHT21_DRV_NAME,
+		.of_match_table = of_match_ptr(sht21_of_match),
+	},
+	.id_table = sht21_id,
+	.probe = sht21_probe,
+	.remove = sht21_remove,
+};
+module_i2c_driver(sht21_driver);
+
+MODULE_DESCRIPTION("Sensirion SHT21 relative humidity and temperature sensor driver");
+MODULE_AUTHOR("Tomasz Duszynski <tduszyns@xxxxxxxxx>");
+MODULE_LICENSE("GPL v2");
--
2.11.1