Re: [PATCH v5] hwmon: Add sht4x Temperature and Humidity Sensor Driver
From: Guenter Roeck
Date: Thu May 13 2021 - 04:45:04 EST
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On Thu, May 13, 2021 at 09:26:09AM +0530, Navin Sankar Velliangiri wrote:
> This patch adds a hwmon driver for the SHT4x Temperature and
> Humidity sensor.
>
> Signed-off-by: Navin Sankar Velliangiri <navin@xxxxxxxxxxx>
>
> Changes in v2:
>
> * Removed unused macro SHT4X_MIN_POLL_INTERVAL
> * Replaced time_after instead of ktime_after
> * Used goto statements for error handling
> * Hardcoded the interval_time instead of clamp_val().
>
> Changes in v3:
>
> * Accept the poll interval if it is greater than SHT4X_MIN_POLL_INTERVAL and
> return -EINVAL for negative values & less than SHT4X_MIN_POLL_INTERVAL
> * Changed the data type of update_interval and last_updated to long.
>
> Changes in v4:
>
> * "update_interval" is long but msecs_to_jiffies() accepts only unsigned int.
> clamp_val() api is used to assign the update_interval stays within UINT_MAX.
>
> Changes in v5:
>
> * Added error handling when master unable to send the data.
> ---
> Documentation/hwmon/index.rst | 1 +
> Documentation/hwmon/sht4x.rst | 45 +++++
> drivers/hwmon/Kconfig | 11 ++
> drivers/hwmon/Makefile | 1 +
> drivers/hwmon/sht4x.c | 307 ++++++++++++++++++++++++++++++++++
> 5 files changed, 365 insertions(+)
> create mode 100644 Documentation/hwmon/sht4x.rst
> create mode 100644 drivers/hwmon/sht4x.c
>
> diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
> index 8d5a2df1ecb6..2a20c6616e21 100644
> --- a/Documentation/hwmon/index.rst
> +++ b/Documentation/hwmon/index.rst
> @@ -160,6 +160,7 @@ Hardware Monitoring Kernel Drivers
> sht15
> sht21
> sht3x
> + sht4x
> shtc1
> sis5595
> sl28cpld
> diff --git a/Documentation/hwmon/sht4x.rst b/Documentation/hwmon/sht4x.rst
> new file mode 100644
> index 000000000000..3b37abcd4a46
> --- /dev/null
> +++ b/Documentation/hwmon/sht4x.rst
> @@ -0,0 +1,45 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +Kernel driver sht4x
> +===================
> +
> +Supported Chips:
> +
> + * Sensirion SHT4X
> +
> + Prefix: 'sht4x'
> +
> + Addresses scanned: None
> +
> + Datasheet:
> +
> + English: https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/2_Humidity_Sensors/Datasheets/Sensirion_Humidity_Sensors_SHT4x_Datasheet.pdf
> +
> +Author: Navin Sankar Velliangiri <navin@xxxxxxxxxxx>
> +
> +
> +Description
> +-----------
> +
> +This driver implements support for the Sensirion SHT4x chip, a humidity
> +and temperature sensor. Temperature is measured in degree celsius, relative
> +humidity is expressed as a percentage. In sysfs interface, all values are
> +scaled by 1000, i.e. the value for 31.5 degrees celsius is 31500.
> +
> +Usage Notes
> +-----------
> +
> +The device communicates with the I2C protocol. Sensors can have the I2C
> +address 0x44. See Documentation/i2c/instantiating-devices.rst for methods
> +to instantiate the device.
> +
> +Sysfs entries
> +-------------
> +
> +=============== ============================================
> +temp1_input Measured temperature in millidegrees Celcius
> +humidity1_input Measured humidity in %H
> +update_interval The minimum interval for polling the sensor,
> + in milliseconds. Writable. Must be at least
> + 2000.
> +============== =============================================
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index 54f04e61fb83..0640e510f3c8 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -1583,6 +1583,17 @@ config SENSORS_SHT3x
> This driver can also be built as a module. If so, the module
> will be called sht3x.
>
> +config SENSORS_SHT4x
> + tristate "Sensiron humidity and temperature sensors. SHT4x and compat."
> + depends on I2C
> + select CRC8
> + help
> + If you say yes here you get support for the Sensiron SHT40, SHT41 and
> + SHT45 humidity and temperature sensors.
> +
> + This driver can also be built as a module. If so, the module
> + will be called sht4x.
> +
> config SENSORS_SHTC1
> tristate "Sensiron humidity and temperature sensors. SHTC1 and compat."
> depends on I2C
> diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
> index fe38e8a5c979..62cee3e03c7f 100644
> --- a/drivers/hwmon/Makefile
> +++ b/drivers/hwmon/Makefile
> @@ -170,6 +170,7 @@ obj-$(CONFIG_SENSORS_SL28CPLD) += sl28cpld-hwmon.o
> obj-$(CONFIG_SENSORS_SHT15) += sht15.o
> obj-$(CONFIG_SENSORS_SHT21) += sht21.o
> obj-$(CONFIG_SENSORS_SHT3x) += sht3x.o
> +obj-$(CONFIG_SENSORS_SHT4x) += sht4x.o
> obj-$(CONFIG_SENSORS_SHTC1) += shtc1.o
> obj-$(CONFIG_SENSORS_SIS5595) += sis5595.o
> obj-$(CONFIG_SENSORS_SMM665) += smm665.o
> diff --git a/drivers/hwmon/sht4x.c b/drivers/hwmon/sht4x.c
> new file mode 100644
> index 000000000000..e1602dc794fb
> --- /dev/null
> +++ b/drivers/hwmon/sht4x.c
> @@ -0,0 +1,307 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +/*
> + * Copyright (c) Linumiz 2021
> + *
> + * sht4x.c - Linux hwmon driver for SHT4x Temperature and Humidity sensor
> + *
> + * Author: Navin Sankar Velliangiri <navin@xxxxxxxxxxx>
> + */
> +
> +#include <linux/crc8.h>
> +#include <linux/delay.h>
> +#include <linux/hwmon.h>
> +#include <linux/i2c.h>
> +#include <linux/jiffies.h>
> +#include <linux/module.h>
> +
> +/*
> + * Poll intervals (in milliseconds)
> + */
> +#define SHT4X_MIN_POLL_INTERVAL 2000
> +
> +/*
> + * I2C command delays (in microseconds)
> + */
> +#define SHT4X_MEAS_DELAY 1000
> +#define SHT4X_DELAY_EXTRA 10000
> +
> +/*
> + * Command Bytes
> + */
> +#define SHT4X_CMD_MEASURE_HPM 0b11111101
> +#define SHT4X_CMD_RESET 0b10010100
> +
> +#define SHT4X_CMD_LEN 1
> +#define SHT4X_CRC8_LEN 1
> +#define SHT4X_WORD_LEN 2
> +#define SHT4X_RESPONSE_LENGTH 6
> +#define SHT4X_CRC8_POLYNOMIAL 0x31
> +#define SHT4X_CRC8_INIT 0xff
> +#define SHT4X_MIN_TEMPERATURE -45000
> +#define SHT4X_MAX_TEMPERATURE 125000
> +#define SHT4X_MIN_HUMIDITY 0
> +#define SHT4X_MAX_HUMIDITY 100000
> +
> +DECLARE_CRC8_TABLE(sht4x_crc8_table);
> +
> +/**
> + * struct sht4x_data - All the data required to operate an SHT4X chip
> + * @client: the i2c client associated with the SHT4X
> + * @lock: a mutex that is used to prevent parallel access to the i2c client
> + * @update_interval: the minimum poll interval
> + * @last_updated: the previous time that the SHT4X was polled
> + * @temperature: the latest temperature value received from the SHT4X
> + * @humidity: the latest humidity value received from the SHT4X
> + */
> +struct sht4x_data {
> + struct i2c_client *client;
> + struct mutex lock; /* atomic read data updates */
> + bool valid; /* validity of fields below */
> + long update_interval; /* in milli-seconds */
> + long last_updated; /* in jiffies */
> + s32 temperature;
> + s32 humidity;
> +};
> +
> +/**
> + * sht4x_read_values() - read and parse the raw data from the SHT4X
> + * @sht4x_data: the struct sht4x_data to use for the lock
> + * Return: 0 if succesfull, 1 if not
> + */
> +static int sht4x_read_values(struct sht4x_data *data)
> +{
> + int ret;
> + u16 t_ticks, rh_ticks;
> + unsigned long next_update;
> + struct i2c_client *client = data->client;
> + u8 crc, raw_data[SHT4X_RESPONSE_LENGTH],
> + cmd[] = {SHT4X_CMD_MEASURE_HPM};
> +
> + mutex_lock(&data->lock);
> + next_update = data->last_updated +
> + msecs_to_jiffies(data->update_interval);
> + if (!data->valid || time_after(jiffies, next_update)) {
> + ret = i2c_master_send(client, cmd, SHT4X_CMD_LEN);
> + if (ret < 0)
> + goto unlock;
> +
> + usleep_range(SHT4X_MEAS_DELAY,
> + SHT4X_MEAS_DELAY + SHT4X_DELAY_EXTRA);
> +
> + ret = i2c_master_recv(client, raw_data, SHT4X_RESPONSE_LENGTH);
> + if (ret != SHT4X_RESPONSE_LENGTH) {
> + if (ret >= 0)
> + ret = -ENODATA;
> +
> + goto unlock;
> + }
> +
> + t_ticks = raw_data[0] << 8 | raw_data[1];
> + rh_ticks = raw_data[3] << 8 | raw_data[4];
> +
> + crc = crc8(sht4x_crc8_table, &raw_data[0], SHT4X_WORD_LEN, CRC8_INIT_VALUE);
> + if (crc != raw_data[2]) {
> + dev_err(&client->dev, "data integrity check failed\n");
> + ret = -EIO;
> + goto unlock;
> + }
> +
> + crc = crc8(sht4x_crc8_table, &raw_data[3], SHT4X_WORD_LEN, CRC8_INIT_VALUE);
> + if (crc != raw_data[5]) {
> + dev_err(&client->dev, "data integrity check failed\n");
> + ret = -EIO;
> + goto unlock;
> + }
> +
> + data->temperature = ((21875 * (int32_t)t_ticks) >> 13) - 45000;
> + data->humidity = ((15625 * (int32_t)rh_ticks) >> 13) - 6000;
> + data->last_updated = jiffies;
> + data->valid = true;
> + }
> +
> +unlock:
> + mutex_unlock(&data->lock);
> + return ret;
> +}
> +
> +static ssize_t sht4x_interval_write(struct sht4x_data *data,
> + long val)
> +{
> + if (val < SHT4X_MIN_POLL_INTERVAL)
> + return -EINVAL;
> +
I don't see the point of rejecting small values (and expecting the user
to know what the minimum value is).
>From sysfs ABI:
"What to do if a value is found to be invalid, depends on the type of the
sysfs attribute that is being set. If it is a continuous setting like a
tempX_max or inX_max attribute, then the value should be clamped to its
limits using clamp_val(value, min_limit, max_limit). If it is not continuous
like for example a tempX_type, then when an invalid value is written,
-EINVAL should be returned."
> +
> + data->update_interval = clamp_val(val, SHT4X_MIN_POLL_INTERVAL,
> + UINT_MAX);
Please keep it simple and just use clamp_val(). I really do not understand
why we have to keep arguing about this. Do I need to clarify the ABI
document to make it easier to understand ? How do I need to phrase
it to explain more clearly what should be done here ?
Thanks,
Guenter
> +
> + return 0;
> +}
> +
> +/**
> + * sht4x_interval_read() - read the minimum poll interval
> + * in milliseconds
> + */
> +static size_t sht4x_interval_read(struct sht4x_data *data,
> + long *val)
> +{
> + *val = data->update_interval;
> + return 0;
> +}
> +
> +/**
> + * sht4x_temperature1_read() - read the temperature in millidegrees
> + */
> +static int sht4x_temperature1_read(struct sht4x_data *data, long *val)
> +{
> + int ret;
> +
> + ret = sht4x_read_values(data);
> + if (ret < 0)
> + return ret;
> +
> + *val = data->temperature;
> +
> + return 0;
> +}
> +
> +/**
> + * sht4x_humidity1_read() - read a relative humidity in millipercent
> + */
> +static int sht4x_humidity1_read(struct sht4x_data *data, long *val)
> +{
> + int ret;
> +
> + ret = sht4x_read_values(data);
> + if (ret < 0)
> + return ret;
> +
> + *val = data->humidity;
> +
> + return 0;
> +}
> +
> +static umode_t sht4x_hwmon_visible(const void *data,
> + enum hwmon_sensor_types type,
> + u32 attr, int channel)
> +{
> + switch (type) {
> + case hwmon_temp:
> + case hwmon_humidity:
> + return 0444;
> + case hwmon_chip:
> + return 0644;
> + default:
> + return 0;
> + }
> +}
> +
> +static int sht4x_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
> + u32 attr, int channel, long *val)
> +{
> + struct sht4x_data *data = dev_get_drvdata(dev);
> +
> + switch (type) {
> + case hwmon_temp:
> + return sht4x_temperature1_read(data, val);
> + case hwmon_humidity:
> + return sht4x_humidity1_read(data, val);
> + case hwmon_chip:
> + return sht4x_interval_read(data, val);
> + default:
> + return -EOPNOTSUPP;
> + }
> +}
> +
> +static int sht4x_hwmon_write(struct device *dev, enum hwmon_sensor_types type,
> + u32 attr, int channel, long val)
> +{
> + struct sht4x_data *data = dev_get_drvdata(dev);
> +
> + switch (type) {
> + case hwmon_chip:
> + return sht4x_interval_write(data, val);
> + default:
> + return -EOPNOTSUPP;
> + }
> +}
> +
> +static const struct hwmon_channel_info *sht4x_info[] = {
> + HWMON_CHANNEL_INFO(chip, HWMON_C_UPDATE_INTERVAL),
> + HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT),
> + HWMON_CHANNEL_INFO(humidity, HWMON_H_INPUT),
> + NULL,
> +};
> +
> +static const struct hwmon_ops sht4x_hwmon_ops = {
> + .is_visible = sht4x_hwmon_visible,
> + .read = sht4x_hwmon_read,
> + .write = sht4x_hwmon_write,
> +};
> +
> +static const struct hwmon_chip_info sht4x_chip_info = {
> + .ops = &sht4x_hwmon_ops,
> + .info = sht4x_info,
> +};
> +
> +static int sht4x_probe(struct i2c_client *client,
> + const struct i2c_device_id *sht4x_id)
> +{
> + struct device *device = &client->dev;
> + struct device *hwmon_dev;
> + struct sht4x_data *data;
> + u8 cmd[] = {SHT4X_CMD_RESET};
> + int ret;
> +
> + /*
> + * we require full i2c support since the sht4x uses multi-byte read and
> + * writes as well as multi-byte commands which are not supported by
> + * the smbus protocol
> + */
> + if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
> + return -EOPNOTSUPP;
> +
> + data = devm_kzalloc(device, sizeof(*data), GFP_KERNEL);
> + if (!data)
> + return -ENOMEM;
> +
> + data->update_interval = SHT4X_MIN_POLL_INTERVAL;
> + data->client = client;
> +
> + mutex_init(&data->lock);
> +
> + crc8_populate_msb(sht4x_crc8_table, SHT4X_CRC8_POLYNOMIAL);
> +
> + ret = i2c_master_send(client, cmd, SHT4X_CMD_LEN);
> + if (ret < 0)
> + return ret;
> + if (ret != SHT4X_CMD_LEN)
> + return -EIO;
> +
> + hwmon_dev = devm_hwmon_device_register_with_info(device,
> + client->name,
> + data,
> + &sht4x_chip_info,
> + NULL);
> +
> + return PTR_ERR_OR_ZERO(hwmon_dev);
> +}
> +
> +static const struct i2c_device_id sht4x_id[] = {
> + { "sht4x", 0 },
> + { },
> +};
> +MODULE_DEVICE_TABLE(i2c, sht4x_id);
> +
> +static struct i2c_driver sht4x_driver = {
> + .driver = {
> + .name = "sht4x",
> + },
> + .probe = sht4x_probe,
> + .id_table = sht4x_id,
> +};
> +
> +module_i2c_driver(sht4x_driver);
> +
> +MODULE_AUTHOR("Navin Sankar Velliangiri <navin@xxxxxxxxxxx>");
> +MODULE_DESCRIPTION("Sensirion SHT4x humidity and temperature sensor driver");
> +MODULE_LICENSE("GPL v2");