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
46DECLARE_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 * @valid: validity of fields below
53 * @update_interval: the minimum poll interval
54 * @last_updated: the previous time that the SHT4X was polled
55 * @temperature: the latest temperature value received from the SHT4X
56 * @humidity: the latest humidity value received from the SHT4X
57 */
58struct sht4x_data {
59	struct i2c_client	*client;
60	struct mutex		lock;	/* atomic read data updates */
61	bool			valid;	/* validity of fields below */
62	long			update_interval;	/* in milli-seconds */
63	long			last_updated;	/* in jiffies */
64	s32			temperature;
65	s32			humidity;
66};
67
68/**
69 * sht4x_read_values() - read and parse the raw data from the SHT4X
70 * @data: the struct sht4x_data to use for the lock
71 * Return: 0 if successful, -ERRNO if not
72 */
73static int sht4x_read_values(struct sht4x_data *data)
74{
75	int ret = 0;
76	u16 t_ticks, rh_ticks;
77	unsigned long next_update;
78	struct i2c_client *client = data->client;
79	u8 crc;
80	u8 cmd[SHT4X_CMD_LEN] = {SHT4X_CMD_MEASURE_HPM};
81	u8 raw_data[SHT4X_RESPONSE_LENGTH];
82
83	mutex_lock(&data->lock);
84	next_update = data->last_updated +
85		      msecs_to_jiffies(data->update_interval);
86
87	if (data->valid && time_before_eq(jiffies, next_update))
88		goto unlock;
89
90	ret = i2c_master_send(client, cmd, SHT4X_CMD_LEN);
91	if (ret < 0)
92		goto unlock;
93
94	usleep_range(SHT4X_MEAS_DELAY_HPM, SHT4X_MEAS_DELAY_HPM + SHT4X_DELAY_EXTRA);
95
96	ret = i2c_master_recv(client, raw_data, SHT4X_RESPONSE_LENGTH);
97	if (ret != SHT4X_RESPONSE_LENGTH) {
98		if (ret >= 0)
99			ret = -ENODATA;
100		goto unlock;
101	}
102
103	t_ticks = raw_data[0] << 8 | raw_data[1];
104	rh_ticks = raw_data[3] << 8 | raw_data[4];
105
106	crc = crc8(sht4x_crc8_table, &raw_data[0], SHT4X_WORD_LEN, CRC8_INIT_VALUE);
107	if (crc != raw_data[2]) {
108		dev_err(&client->dev, "data integrity check failed\n");
109		ret = -EIO;
110		goto unlock;
111	}
112
113	crc = crc8(sht4x_crc8_table, &raw_data[3], SHT4X_WORD_LEN, CRC8_INIT_VALUE);
114	if (crc != raw_data[5]) {
115		dev_err(&client->dev, "data integrity check failed\n");
116		ret = -EIO;
117		goto unlock;
118	}
119
120	data->temperature = ((21875 * (int32_t)t_ticks) >> 13) - 45000;
121	data->humidity = ((15625 * (int32_t)rh_ticks) >> 13) - 6000;
122	data->last_updated = jiffies;
123	data->valid = true;
124	ret = 0;
125
126unlock:
127	mutex_unlock(&data->lock);
128	return ret;
129}
130
131static ssize_t sht4x_interval_write(struct sht4x_data *data, long val)
132{
133	data->update_interval = clamp_val(val, SHT4X_MIN_POLL_INTERVAL, INT_MAX);
134
135	return 0;
136}
137
138/* sht4x_interval_read() - read the minimum poll interval in milliseconds */
139static size_t sht4x_interval_read(struct sht4x_data *data, long *val)
140{
141	*val = data->update_interval;
142	return 0;
143}
144
145/* sht4x_temperature1_read() - read the temperature in millidegrees */
146static int sht4x_temperature1_read(struct sht4x_data *data, long *val)
147{
148	int ret;
149
150	ret = sht4x_read_values(data);
151	if (ret < 0)
152		return ret;
153
154	*val = data->temperature;
155
156	return 0;
157}
158
159/* sht4x_humidity1_read() - read a relative humidity in millipercent */
160static int sht4x_humidity1_read(struct sht4x_data *data, long *val)
161{
162	int ret;
163
164	ret = sht4x_read_values(data);
165	if (ret < 0)
166		return ret;
167
168	*val = data->humidity;
169
170	return 0;
171}
172
173static umode_t sht4x_hwmon_visible(const void *data,
174				   enum hwmon_sensor_types type,
175				   u32 attr, int channel)
176{
177	switch (type) {
178	case hwmon_temp:
179	case hwmon_humidity:
180		return 0444;
181	case hwmon_chip:
182		return 0644;
183	default:
184		return 0;
185	}
186}
187
188static int sht4x_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
189			    u32 attr, int channel, long *val)
190{
191	struct sht4x_data *data = dev_get_drvdata(dev);
192
193	switch (type) {
194	case hwmon_temp:
195		return sht4x_temperature1_read(data, val);
196	case hwmon_humidity:
197		return sht4x_humidity1_read(data, val);
198	case hwmon_chip:
199		return sht4x_interval_read(data, val);
200	default:
201		return -EOPNOTSUPP;
202	}
203}
204
205static int sht4x_hwmon_write(struct device *dev, enum hwmon_sensor_types type,
206			     u32 attr, int channel, long val)
207{
208	struct sht4x_data *data = dev_get_drvdata(dev);
209
210	switch (type) {
211	case hwmon_chip:
212		return sht4x_interval_write(data, val);
213	default:
214		return -EOPNOTSUPP;
215	}
216}
217
218static const struct hwmon_channel_info * const sht4x_info[] = {
219	HWMON_CHANNEL_INFO(chip, HWMON_C_UPDATE_INTERVAL),
220	HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT),
221	HWMON_CHANNEL_INFO(humidity, HWMON_H_INPUT),
222	NULL,
223};
224
225static const struct hwmon_ops sht4x_hwmon_ops = {
226	.is_visible = sht4x_hwmon_visible,
227	.read = sht4x_hwmon_read,
228	.write = sht4x_hwmon_write,
229};
230
231static const struct hwmon_chip_info sht4x_chip_info = {
232	.ops = &sht4x_hwmon_ops,
233	.info = sht4x_info,
234};
235
236static int sht4x_probe(struct i2c_client *client)
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
278static const struct i2c_device_id sht4x_id[] = {
279	{ "sht4x", 0 },
280	{ },
281};
282MODULE_DEVICE_TABLE(i2c, sht4x_id);
283
284static const struct of_device_id sht4x_of_match[] = {
285	{ .compatible = "sensirion,sht4x" },
286	{ }
287};
288MODULE_DEVICE_TABLE(of, sht4x_of_match);
289
290static 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
299module_i2c_driver(sht4x_driver);
300
301MODULE_AUTHOR("Navin Sankar Velliangiri <navin@linumiz.com>");
302MODULE_DESCRIPTION("Sensirion SHT4x humidity and temperature sensor driver");
303MODULE_LICENSE("GPL v2");
304