Re: [PATCH v6] hwmon: Add sht4x Temperature and Humidity Sensor Driver

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On 5/21/21 11:09 PM, 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.

Changes in v6:

* clamp_val() alone is used to set the update interval. since the update
   interval is a continuous setting.
---
  Documentation/hwmon/index.rst |   1 +
  Documentation/hwmon/sht4x.rst |  45 +++++
  drivers/hwmon/Kconfig         |  11 ++
  drivers/hwmon/Makefile        |   1 +
  drivers/hwmon/sht4x.c         | 305 ++++++++++++++++++++++++++++++++++
  5 files changed, 363 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 9ed60fa84cbe..b6fcae40258c 100644
--- a/Documentation/hwmon/index.rst
+++ b/Documentation/hwmon/index.rst
@@ -164,6 +164,7 @@ 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 87624902ea80..e3675377bc5d 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 59e78bc212cf..d712c61c1f5e 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -171,6 +171,7 @@ 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..39e1b4a123fa
--- /dev/null
+++ b/drivers/hwmon/sht4x.c
@@ -0,0 +1,305 @@
+// 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;

Ah yes, the value of ret will be uninitialized, and the function will return
a random value if data->valid is false or if two measurements follow each other.

Please fix and resubmit. The driver looks good otherwise.

Guenter



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