Date:   Sun, 19 Feb 2017 17:38:50 +0100 (CET)
From:   Peter Meerwald-Stadler <pmeerw@...erw.net>
To:     Tomasz Duszynski <tduszyns@...il.com>
cc:     linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
        jic23@...nel.org, knaack.h@....de, lars@...afoo.de
Subject: Re: [PATCH 1/3] iio: humidity: add sht21 relative humidity and
 temperature sensor driver


> 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.

comments below
 
> 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>
> ---
>  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

select IIO_BUFFER
select IIO_TRIGGERED_BUFFER

> +	help
> +	  Say yes here to build support for the  Sensirion SHT21 relative

two spaces before Sensirion

> +	  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,

I'd prefix these as well

> +	RES_8_12,
> +	RES_10_13,
> +	RES_11_11,
> +};
> +
> +/*
> + * Combined sampling frequency i.e measuring RH and T together, which seems

i.e.

> + * 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)

returns bool?

> +{
> +	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;

ret initialization not needed

> +	__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;

default:
return -EINVAL;
?

> +	}
> +
> +	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);

wondering if negative values are properly sign-extended?

I'd prefer a bit of code duplication if the ugliness above can be avoided

> +
> +	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);

simplify, just
mutex_unlock(&state->lock);
return ret;

> +	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;

can't this be expressed using _SCALE and _OFFSET?
I think that is the preferred way

> +
> +	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);

this should raise a checkpatch warning...
20ms should be fine

> +
> +	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))

use iio_device_claim_direct_mode()

> +			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
> 

-- 

Peter Meerwald-Stadler
+43-664-2444418 (mobile)

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