[PATCH v2 2/2] hwmon: (sht4x): Add support for Sensirion STS4x temperature sensors

The Sensirion STS4x series is the temperature-only variant of the
SHT4x family. It shares the same I2C command set, conversion formulas,
CRC checksum, and timing with the SHT4x, but only returns temperature
data (3 bytes: 2 data bytes + 1 CRC byte).

Add support for the STS4x series by dynamically adjusting the read
response length, suppressing humidity channel attributes when probed
as STS4x, and omitting heater sysfs attributes.

Link: https://sensirion.com/resource/datasheet/sts4x
Signed-off-by: Alessandro Zini <[email protected]>
---
Changes in v2:
- Unconditionally initialize data->heating_complete in probe to avoid
  an msleep delay on boot with INITIAL_JIFFIES.
- Bypass heater delay checks in sht4x_read_values() when chip is sts4x.

 Documentation/hwmon/sht4x.rst | 17 ++++++++--
 drivers/hwmon/sht4x.c         | 62 +++++++++++++++++++++++++----------
 2 files changed, 59 insertions(+), 20 deletions(-)

diff --git a/Documentation/hwmon/sht4x.rst b/Documentation/hwmon/sht4x.rst
index ba094ad0e2816..b9564632a1be2 100644
--- a/Documentation/hwmon/sht4x.rst
+++ b/Documentation/hwmon/sht4x.rst
@@ -15,6 +15,16 @@ Supported Chips:
 
       English: https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/2_Humidity_Sensors/Datasheets/Sensirion_Humidity_Sensors_SHT4x_Datasheet.pdf
 
+  * Sensirion STS4X
+
+    Prefix: 'sts4x'
+
+    Addresses scanned: None
+
+    Datasheet:
+
+      English: https://sensirion.com/resource/datasheet/sts4x
+
 Author: Navin Sankar Velliangiri <[email protected]>
 
 
@@ -22,9 +32,10 @@ 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.
+and temperature sensor, and the Sensirion STS4x chip, a temperature sensor.
+Temperature is measured in degree celsius, relative humidity is expressed as a
+percentage (on SHT4x only). In sysfs interface, all values are scaled by 1000,
+i.e. the value for 31.5 degrees celsius is 31500.
 
 Usage Notes
 -----------
diff --git a/drivers/hwmon/sht4x.c b/drivers/hwmon/sht4x.c
index 9cace0e8acdab..daca24cfbcd52 100644
--- a/drivers/hwmon/sht4x.c
+++ b/drivers/hwmon/sht4x.c
@@ -43,6 +43,7 @@
 #define SHT4X_CRC8_LEN		1
 #define SHT4X_WORD_LEN		2
 #define SHT4X_RESPONSE_LENGTH	6
+#define STS4X_RESPONSE_LENGTH	3
 #define SHT4X_CRC8_POLYNOMIAL	0x31
 #define SHT4X_CRC8_INIT		0xff
 #define SHT4X_MIN_TEMPERATURE	-45000
@@ -52,9 +53,15 @@
 
 DECLARE_CRC8_TABLE(sht4x_crc8_table);
 
+enum sht4x_chips {
+	sht4x,
+	sts4x,
+};
+
 /**
  * struct sht4x_data - All the data required to operate an SHT4X chip
  * @client: the i2c client associated with the SHT4X
+ * @chip_id: the chip type (sht4x or sts4x)
  * @heating_complete: the time that the last heating finished
  * @data_pending: true if and only if there are measurements to retrieve after heating
  * @heater_power: the power at which the heater will be started
@@ -67,6 +74,7 @@ DECLARE_CRC8_TABLE(sht4x_crc8_table);
  */
 struct sht4x_data {
 	struct i2c_client	*client;
+	enum sht4x_chips	chip_id;
 	unsigned long		heating_complete;	/* in jiffies */
 	bool			data_pending;
 	u32			heater_power;	/* in milli-watts */
@@ -92,11 +100,15 @@ static int sht4x_read_values(struct sht4x_data *data)
 	u8 crc;
 	u8 cmd[SHT4X_CMD_LEN] = {SHT4X_CMD_MEASURE_HPM};
 	u8 raw_data[SHT4X_RESPONSE_LENGTH];
+	size_t response_length = data->chip_id == sts4x ?
+				 STS4X_RESPONSE_LENGTH : SHT4X_RESPONSE_LENGTH;
 	unsigned long curr_jiffies;
 
-	curr_jiffies = jiffies;
-	if (time_before(curr_jiffies, data->heating_complete))
-		msleep(jiffies_to_msecs(data->heating_complete - curr_jiffies));
+	if (data->chip_id != sts4x) {
+		curr_jiffies = jiffies;
+		if (time_before(curr_jiffies, data->heating_complete))
+			msleep(jiffies_to_msecs(data->heating_complete - curr_jiffies));
+	}
 
 	if (data->data_pending &&
 	    time_before(jiffies, data->heating_complete + data->update_interval)) {
@@ -115,15 +127,14 @@ static int sht4x_read_values(struct sht4x_data *data)
 		usleep_range(SHT4X_MEAS_DELAY_HPM, SHT4X_MEAS_DELAY_HPM + SHT4X_DELAY_EXTRA);
 	}
 
-	ret = i2c_master_recv(client, raw_data, SHT4X_RESPONSE_LENGTH);
-	if (ret != SHT4X_RESPONSE_LENGTH) {
+	ret = i2c_master_recv(client, raw_data, response_length);
+	if (ret != response_length) {
 		if (ret >= 0)
 			ret = -ENODATA;
 		return ret;
 	}
 
 	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]) {
@@ -131,14 +142,19 @@ static int sht4x_read_values(struct sht4x_data *data)
 		return -EIO;
 	}
 
-	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");
-		return -EIO;
+	data->temperature = ((21875 * (int32_t)t_ticks) >> 13) - 45000;
+
+	if (data->chip_id != sts4x) {
+		rh_ticks = raw_data[3] << 8 | raw_data[4];
+		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");
+			return -EIO;
+		}
+
+		data->humidity = ((15625 * (int32_t)rh_ticks) >> 13) - 6000;
 	}
 
-	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;
 	return 0;
@@ -190,9 +206,14 @@ static umode_t sht4x_hwmon_visible(const void *data,
 				   enum hwmon_sensor_types type,
 				   u32 attr, int channel)
 {
+	const struct sht4x_data *chip_data = data;
+
 	switch (type) {
 	case hwmon_temp:
+		return 0444;
 	case hwmon_humidity:
+		if (chip_data->chip_id == sts4x)
+			return 0;
 		return 0444;
 	case hwmon_chip:
 		return 0644;
@@ -382,6 +403,7 @@ static const struct hwmon_chip_info sht4x_chip_info = {
 
 static int sht4x_probe(struct i2c_client *client)
 {
+	const struct attribute_group **groups = NULL;
 	struct device *device = &client->dev;
 	struct device *hwmon_dev;
 	struct sht4x_data *data;
@@ -400,11 +422,15 @@ static int sht4x_probe(struct i2c_client *client)
 	if (!data)
 		return -ENOMEM;
 
+	data->chip_id = (uintptr_t)i2c_get_match_data(client);
 	data->update_interval = SHT4X_MIN_POLL_INTERVAL;
 	data->client = client;
-	data->heater_power = 200;
-	data->heater_time = 1000;
 	data->heating_complete = jiffies;
+	if (data->chip_id != sts4x) {
+		data->heater_power = 200;
+		data->heater_time = 1000;
+		groups = sht4x_groups;
+	}
 
 	crc8_populate_msb(sht4x_crc8_table, SHT4X_CRC8_POLYNOMIAL);
 
@@ -418,19 +444,21 @@ static int sht4x_probe(struct i2c_client *client)
 							 client->name,
 							 data,
 							 &sht4x_chip_info,
-							 sht4x_groups);
+							 groups);
 
 	return PTR_ERR_OR_ZERO(hwmon_dev);
 }
 
 static const struct i2c_device_id sht4x_id[] = {
-	{ .name = "sht4x" },
+	{ .name = "sht4x", .driver_data = sht4x },
+	{ .name = "sts4x", .driver_data = sts4x },
 	{ }
 };
 MODULE_DEVICE_TABLE(i2c, sht4x_id);
 
 static const struct of_device_id sht4x_of_match[] = {
-	{ .compatible = "sensirion,sht4x" },
+	{ .compatible = "sensirion,sht4x", .data = (void *)sht4x },
+	{ .compatible = "sensirion,sts40", .data = (void *)sts4x },
 	{ }
 };
 MODULE_DEVICE_TABLE(of, sht4x_of_match);
-- 
2.55.0