Message-ID: <20170219173843.GB25989@Arch.lan>
Date:   Sun, 19 Feb 2017 18:38:45 +0100
From:   Tomasz Duszynski <tduszyns@...il.com>
To:     Peter Meerwald-Stadler <pmeerw@...erw.net>
Cc:     Tomasz Duszynski <tduszyns@...il.com>,
        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

On Sun, Feb 19, 2017 at 05:38:50PM +0100, Peter Meerwald-Stadler 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.
>
> 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
Ack
>
> > +	help
> > +	  Say yes here to build support for the  Sensirion SHT21 relative
>
> two spaces before Sensirion
Good catch!
>
> > +	  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
Ack
>
> > +	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?
Bool is also fine. Just thought bools are less common in kernel so
didn't use it.
>
> > +{
> > +	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
This was just to silence compiler warnings about uninitialized variables.
>
> > +	__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;
> ?
Ack
>
> > +	}
> > +
> > +	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
Ack
>
> > +
> > +	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;
Ack
>
> > +	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
No strong opinions on that, drivers seem to use both options.
>
> > +
> > +	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
And it did. Just ignored that.
>
> > +
> > +	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()
Ack
>
> > +			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)

Thanks for review Peter!

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