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Date:   Sun, 19 Feb 2017 15:04:32 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Tomasz Duszynski <tduszyns@...il.com>,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Cc:     knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net,
        Guenter Roeck <linux@...ck-us.net>,
        Jean Delvare <khali@...ux-fr.org>, linux-hwmon@...r.kernel.org
Subject: Re: [PATCH 1/3] iio: humidity: add sht21 relative humidity and
 temperature sensor driver

On 19/02/17 14:58, Tomasz Duszynski wrote:
> 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@...il.com>
Hi Tomasz,

I haven't looked at this yet, but one thing we have to do whenever suggesting
replacement of an hwmon driver is to convince the hwmon guys that it is a
good idea.  

As such I've cc'd Guenter, Jean and the list.

Jonathan

p.s Probably won't get to this today as running out of time.  Depending on
how mad the week is it might be next weekend before I get a chance.
> ---
>  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@...il.com>
> + *
> + * 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@...il.com>");
> +MODULE_LICENSE("GPL v2");
> --
> 2.11.1
> 

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