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1 // SPDX-License-Identifier: GPL-2.0-only
2 
3 /*
4  * Copyright (c) Linumiz 2021
5  *
6  * sht4x.c - Linux hwmon driver for SHT4x Temperature and Humidity sensor
7  *
8  * Author: Navin Sankar Velliangiri <navin@linumiz.com>
9  */
10 
11 #include <linux/crc8.h>
12 #include <linux/delay.h>
13 #include <linux/hwmon.h>
14 #include <linux/i2c.h>
15 #include <linux/jiffies.h>
16 #include <linux/module.h>
17 
18 /*
19  * Poll intervals (in milliseconds)
20  */
21 #define SHT4X_MIN_POLL_INTERVAL	2000
22 
23 /*
24  * I2C command delays (in microseconds)
25  */
26 #define SHT4X_MEAS_DELAY_HPM	8200	/* see t_MEAS,h in datasheet */
27 #define SHT4X_DELAY_EXTRA	10000
28 
29 /*
30  * Command Bytes
31  */
32 #define SHT4X_CMD_MEASURE_HPM	0b11111101
33 #define SHT4X_CMD_RESET		0b10010100
34 
35 #define SHT4X_CMD_LEN		1
36 #define SHT4X_CRC8_LEN		1
37 #define SHT4X_WORD_LEN		2
38 #define SHT4X_RESPONSE_LENGTH	6
39 #define SHT4X_CRC8_POLYNOMIAL	0x31
40 #define SHT4X_CRC8_INIT		0xff
41 #define SHT4X_MIN_TEMPERATURE	-45000
42 #define SHT4X_MAX_TEMPERATURE	125000
43 #define SHT4X_MIN_HUMIDITY	0
44 #define SHT4X_MAX_HUMIDITY	100000
45 
46 DECLARE_CRC8_TABLE(sht4x_crc8_table);
47 
48 /**
49  * struct sht4x_data - All the data required to operate an SHT4X chip
50  * @client: the i2c client associated with the SHT4X
51  * @lock: a mutex that is used to prevent parallel access to the i2c client
52  * @update_interval: the minimum poll interval
53  * @last_updated: the previous time that the SHT4X was polled
54  * @temperature: the latest temperature value received from the SHT4X
55  * @humidity: the latest humidity value received from the SHT4X
56  */
57 struct sht4x_data {
58 	struct i2c_client	*client;
59 	struct mutex		lock;	/* atomic read data updates */
60 	bool			valid;	/* validity of fields below */
61 	long			update_interval;	/* in milli-seconds */
62 	long			last_updated;	/* in jiffies */
63 	s32			temperature;
64 	s32			humidity;
65 };
66 
67 /**
68  * sht4x_read_values() - read and parse the raw data from the SHT4X
69  * @sht4x_data: the struct sht4x_data to use for the lock
70  * Return: 0 if successful, -ERRNO if not
71  */
sht4x_read_values(struct sht4x_data * data)72 static int sht4x_read_values(struct sht4x_data *data)
73 {
74 	int ret = 0;
75 	u16 t_ticks, rh_ticks;
76 	unsigned long next_update;
77 	struct i2c_client *client = data->client;
78 	u8 crc;
79 	u8 cmd[SHT4X_CMD_LEN] = {SHT4X_CMD_MEASURE_HPM};
80 	u8 raw_data[SHT4X_RESPONSE_LENGTH];
81 
82 	mutex_lock(&data->lock);
83 	next_update = data->last_updated +
84 		      msecs_to_jiffies(data->update_interval);
85 
86 	if (data->valid && time_before_eq(jiffies, next_update))
87 		goto unlock;
88 
89 	ret = i2c_master_send(client, cmd, SHT4X_CMD_LEN);
90 	if (ret < 0)
91 		goto unlock;
92 
93 	usleep_range(SHT4X_MEAS_DELAY_HPM, SHT4X_MEAS_DELAY_HPM + SHT4X_DELAY_EXTRA);
94 
95 	ret = i2c_master_recv(client, raw_data, SHT4X_RESPONSE_LENGTH);
96 	if (ret != SHT4X_RESPONSE_LENGTH) {
97 		if (ret >= 0)
98 			ret = -ENODATA;
99 		goto unlock;
100 	}
101 
102 	t_ticks = raw_data[0] << 8 | raw_data[1];
103 	rh_ticks = raw_data[3] << 8 | raw_data[4];
104 
105 	crc = crc8(sht4x_crc8_table, &raw_data[0], SHT4X_WORD_LEN, CRC8_INIT_VALUE);
106 	if (crc != raw_data[2]) {
107 		dev_err(&client->dev, "data integrity check failed\n");
108 		ret = -EIO;
109 		goto unlock;
110 	}
111 
112 	crc = crc8(sht4x_crc8_table, &raw_data[3], SHT4X_WORD_LEN, CRC8_INIT_VALUE);
113 	if (crc != raw_data[5]) {
114 		dev_err(&client->dev, "data integrity check failed\n");
115 		ret = -EIO;
116 		goto unlock;
117 	}
118 
119 	data->temperature = ((21875 * (int32_t)t_ticks) >> 13) - 45000;
120 	data->humidity = ((15625 * (int32_t)rh_ticks) >> 13) - 6000;
121 	data->last_updated = jiffies;
122 	data->valid = true;
123 	ret = 0;
124 
125 unlock:
126 	mutex_unlock(&data->lock);
127 	return ret;
128 }
129 
sht4x_interval_write(struct sht4x_data * data,long val)130 static ssize_t sht4x_interval_write(struct sht4x_data *data, long val)
131 {
132 	data->update_interval = clamp_val(val, SHT4X_MIN_POLL_INTERVAL, INT_MAX);
133 
134 	return 0;
135 }
136 
137 /* sht4x_interval_read() - read the minimum poll interval in milliseconds */
sht4x_interval_read(struct sht4x_data * data,long * val)138 static size_t sht4x_interval_read(struct sht4x_data *data, long *val)
139 {
140 	*val = data->update_interval;
141 	return 0;
142 }
143 
144 /* sht4x_temperature1_read() - read the temperature in millidegrees */
sht4x_temperature1_read(struct sht4x_data * data,long * val)145 static int sht4x_temperature1_read(struct sht4x_data *data, long *val)
146 {
147 	int ret;
148 
149 	ret = sht4x_read_values(data);
150 	if (ret < 0)
151 		return ret;
152 
153 	*val = data->temperature;
154 
155 	return 0;
156 }
157 
158 /* sht4x_humidity1_read() - read a relative humidity in millipercent */
sht4x_humidity1_read(struct sht4x_data * data,long * val)159 static int sht4x_humidity1_read(struct sht4x_data *data, long *val)
160 {
161 	int ret;
162 
163 	ret = sht4x_read_values(data);
164 	if (ret < 0)
165 		return ret;
166 
167 	*val = data->humidity;
168 
169 	return 0;
170 }
171 
sht4x_hwmon_visible(const void * data,enum hwmon_sensor_types type,u32 attr,int channel)172 static umode_t sht4x_hwmon_visible(const void *data,
173 				   enum hwmon_sensor_types type,
174 				   u32 attr, int channel)
175 {
176 	switch (type) {
177 	case hwmon_temp:
178 	case hwmon_humidity:
179 		return 0444;
180 	case hwmon_chip:
181 		return 0644;
182 	default:
183 		return 0;
184 	}
185 }
186 
sht4x_hwmon_read(struct device * dev,enum hwmon_sensor_types type,u32 attr,int channel,long * val)187 static int sht4x_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
188 			    u32 attr, int channel, long *val)
189 {
190 	struct sht4x_data *data = dev_get_drvdata(dev);
191 
192 	switch (type) {
193 	case hwmon_temp:
194 		return sht4x_temperature1_read(data, val);
195 	case hwmon_humidity:
196 		return sht4x_humidity1_read(data, val);
197 	case hwmon_chip:
198 		return sht4x_interval_read(data, val);
199 	default:
200 		return -EOPNOTSUPP;
201 	}
202 }
203 
sht4x_hwmon_write(struct device * dev,enum hwmon_sensor_types type,u32 attr,int channel,long val)204 static int sht4x_hwmon_write(struct device *dev, enum hwmon_sensor_types type,
205 			     u32 attr, int channel, long val)
206 {
207 	struct sht4x_data *data = dev_get_drvdata(dev);
208 
209 	switch (type) {
210 	case hwmon_chip:
211 		return sht4x_interval_write(data, val);
212 	default:
213 		return -EOPNOTSUPP;
214 	}
215 }
216 
217 static const struct hwmon_channel_info *sht4x_info[] = {
218 	HWMON_CHANNEL_INFO(chip, HWMON_C_UPDATE_INTERVAL),
219 	HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT),
220 	HWMON_CHANNEL_INFO(humidity, HWMON_H_INPUT),
221 	NULL,
222 };
223 
224 static const struct hwmon_ops sht4x_hwmon_ops = {
225 	.is_visible = sht4x_hwmon_visible,
226 	.read = sht4x_hwmon_read,
227 	.write = sht4x_hwmon_write,
228 };
229 
230 static const struct hwmon_chip_info sht4x_chip_info = {
231 	.ops = &sht4x_hwmon_ops,
232 	.info = sht4x_info,
233 };
234 
sht4x_probe(struct i2c_client * client,const struct i2c_device_id * sht4x_id)235 static int sht4x_probe(struct i2c_client *client,
236 		       const struct i2c_device_id *sht4x_id)
237 {
238 	struct device *device = &client->dev;
239 	struct device *hwmon_dev;
240 	struct sht4x_data *data;
241 	u8 cmd[] = {SHT4X_CMD_RESET};
242 	int ret;
243 
244 	/*
245 	 * we require full i2c support since the sht4x uses multi-byte read and
246 	 * writes as well as multi-byte commands which are not supported by
247 	 * the smbus protocol
248 	 */
249 	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
250 		return -EOPNOTSUPP;
251 
252 	data = devm_kzalloc(device, sizeof(*data), GFP_KERNEL);
253 	if (!data)
254 		return -ENOMEM;
255 
256 	data->update_interval = SHT4X_MIN_POLL_INTERVAL;
257 	data->client = client;
258 
259 	mutex_init(&data->lock);
260 
261 	crc8_populate_msb(sht4x_crc8_table, SHT4X_CRC8_POLYNOMIAL);
262 
263 	ret = i2c_master_send(client, cmd, SHT4X_CMD_LEN);
264 	if (ret < 0)
265 		return ret;
266 	if (ret != SHT4X_CMD_LEN)
267 		return -EIO;
268 
269 	hwmon_dev = devm_hwmon_device_register_with_info(device,
270 							 client->name,
271 							 data,
272 							 &sht4x_chip_info,
273 							 NULL);
274 
275 	return PTR_ERR_OR_ZERO(hwmon_dev);
276 }
277 
278 static const struct i2c_device_id sht4x_id[] = {
279 	{ "sht4x", 0 },
280 	{ },
281 };
282 MODULE_DEVICE_TABLE(i2c, sht4x_id);
283 
284 static const struct of_device_id sht4x_of_match[] = {
285 	{ .compatible = "sensirion,sht4x" },
286 	{ }
287 };
288 MODULE_DEVICE_TABLE(of, sht4x_of_match);
289 
290 static struct i2c_driver sht4x_driver = {
291 	.driver = {
292 		.name = "sht4x",
293 		.of_match_table = sht4x_of_match,
294 	},
295 	.probe		= sht4x_probe,
296 	.id_table	= sht4x_id,
297 };
298 
299 module_i2c_driver(sht4x_driver);
300 
301 MODULE_AUTHOR("Navin Sankar Velliangiri <navin@linumiz.com>");
302 MODULE_DESCRIPTION("Sensirion SHT4x humidity and temperature sensor driver");
303 MODULE_LICENSE("GPL v2");
304