1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * DHT11/DHT22 bit banging GPIO driver
4 *
5 * Copyright (c) Harald Geyer <harald@ccbib.org>
6 */
7
8 #include <linux/err.h>
9 #include <linux/interrupt.h>
10 #include <linux/device.h>
11 #include <linux/kernel.h>
12 #include <linux/printk.h>
13 #include <linux/slab.h>
14 #include <linux/string_choices.h>
15 #include <linux/sysfs.h>
16 #include <linux/io.h>
17 #include <linux/module.h>
18 #include <linux/platform_device.h>
19 #include <linux/wait.h>
20 #include <linux/bitops.h>
21 #include <linux/completion.h>
22 #include <linux/mutex.h>
23 #include <linux/delay.h>
24 #include <linux/gpio/consumer.h>
25 #include <linux/timekeeping.h>
26
27 #include <linux/iio/iio.h>
28
29 #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */
30
31 #define DHT11_EDGES_PREAMBLE 2
32 #define DHT11_BITS_PER_READ 40
33 /*
34 * Note that when reading the sensor actually 84 edges are detected, but
35 * since the last edge is not significant, we only store 83:
36 */
37 #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \
38 DHT11_EDGES_PREAMBLE + 1)
39
40 /*
41 * Data transmission timing:
42 * Data bits are encoded as pulse length (high time) on the data line.
43 * 0-bit: 22-30uS -- typically 26uS (AM2302)
44 * 1-bit: 68-75uS -- typically 70uS (AM2302)
45 * The acutal timings also depend on the properties of the cable, with
46 * longer cables typically making pulses shorter.
47 *
48 * Our decoding depends on the time resolution of the system:
49 * timeres > 34uS ... don't know what a 1-tick pulse is
50 * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks)
51 * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is
52 * timeres < 23uS ... no problem
53 *
54 * Luckily clocks in the 33-44kHz range are quite uncommon, so we can
55 * support most systems if the threshold for decoding a pulse as 1-bit
56 * is chosen carefully. If somebody really wants to support clocks around
57 * 40kHz, where this driver is most unreliable, there are two options.
58 * a) select an implementation using busy loop polling on those systems
59 * b) use the checksum to do some probabilistic decoding
60 */
61 #define DHT11_START_TRANSMISSION_MIN 18000 /* us */
62 #define DHT11_START_TRANSMISSION_MAX 20000 /* us */
63 #define DHT11_MIN_TIMERES 34000 /* ns */
64 #define DHT11_THRESHOLD 49000 /* ns */
65 #define DHT11_AMBIG_LOW 23000 /* ns */
66 #define DHT11_AMBIG_HIGH 30000 /* ns */
67
68 struct dht11 {
69 struct device *dev;
70
71 struct gpio_desc *gpiod;
72 int irq;
73
74 struct completion completion;
75 /* The iio sysfs interface doesn't prevent concurrent reads: */
76 struct mutex lock;
77
78 s64 timestamp;
79 int temperature;
80 int humidity;
81
82 /* num_edges: -1 means "no transmission in progress" */
83 int num_edges;
84 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ];
85 };
86
87 #ifdef CONFIG_DYNAMIC_DEBUG
88 /*
89 * dht11_edges_print: show the data as actually received by the
90 * driver.
91 */
dht11_edges_print(struct dht11 * dht11)92 static void dht11_edges_print(struct dht11 *dht11)
93 {
94 int i;
95
96 dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);
97 for (i = 1; i < dht11->num_edges; ++i) {
98 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
99 dht11->edges[i].ts - dht11->edges[i - 1].ts,
100 str_high_low(dht11->edges[i - 1].value));
101 }
102 }
103 #endif /* CONFIG_DYNAMIC_DEBUG */
104
dht11_decode_byte(char * bits)105 static unsigned char dht11_decode_byte(char *bits)
106 {
107 unsigned char ret = 0;
108 int i;
109
110 for (i = 0; i < 8; ++i) {
111 ret <<= 1;
112 if (bits[i])
113 ++ret;
114 }
115
116 return ret;
117 }
118
dht11_decode(struct dht11 * dht11,int offset)119 static int dht11_decode(struct dht11 *dht11, int offset)
120 {
121 int i, t;
122 char bits[DHT11_BITS_PER_READ];
123 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
124
125 for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
126 t = dht11->edges[offset + 2 * i + 2].ts -
127 dht11->edges[offset + 2 * i + 1].ts;
128 if (!dht11->edges[offset + 2 * i + 1].value) {
129 dev_dbg(dht11->dev,
130 "lost synchronisation at edge %d\n",
131 offset + 2 * i + 1);
132 return -EIO;
133 }
134 bits[i] = t > DHT11_THRESHOLD;
135 }
136
137 hum_int = dht11_decode_byte(bits);
138 hum_dec = dht11_decode_byte(&bits[8]);
139 temp_int = dht11_decode_byte(&bits[16]);
140 temp_dec = dht11_decode_byte(&bits[24]);
141 checksum = dht11_decode_byte(&bits[32]);
142
143 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {
144 dev_dbg(dht11->dev, "invalid checksum\n");
145 return -EIO;
146 }
147
148 dht11->timestamp = ktime_get_boottime_ns();
149 if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */
150 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
151 ((temp_int & 0x80) ? -100 : 100);
152 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
153 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */
154 dht11->temperature = temp_int * 1000;
155 dht11->humidity = hum_int * 1000;
156 } else {
157 dev_err(dht11->dev,
158 "Don't know how to decode data: %d %d %d %d\n",
159 hum_int, hum_dec, temp_int, temp_dec);
160 return -EIO;
161 }
162
163 return 0;
164 }
165
166 /*
167 * IRQ handler called on GPIO edges
168 */
dht11_handle_irq(int irq,void * data)169 static irqreturn_t dht11_handle_irq(int irq, void *data)
170 {
171 struct iio_dev *iio = data;
172 struct dht11 *dht11 = iio_priv(iio);
173
174 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
175 dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns();
176 dht11->edges[dht11->num_edges++].value =
177 gpiod_get_value(dht11->gpiod);
178
179 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
180 complete(&dht11->completion);
181 }
182
183 return IRQ_HANDLED;
184 }
185
dht11_read_raw(struct iio_dev * iio_dev,const struct iio_chan_spec * chan,int * val,int * val2,long m)186 static int dht11_read_raw(struct iio_dev *iio_dev,
187 const struct iio_chan_spec *chan,
188 int *val, int *val2, long m)
189 {
190 struct dht11 *dht11 = iio_priv(iio_dev);
191 int ret, timeres, offset;
192
193 mutex_lock(&dht11->lock);
194 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boottime_ns()) {
195 timeres = ktime_get_resolution_ns();
196 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);
197 if (timeres > DHT11_MIN_TIMERES) {
198 dev_err(dht11->dev, "timeresolution %dns too low\n",
199 timeres);
200 /* In theory a better clock could become available
201 * at some point ... and there is no error code
202 * that really fits better.
203 */
204 ret = -EAGAIN;
205 goto err;
206 }
207 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)
208 dev_warn(dht11->dev,
209 "timeresolution: %dns - decoding ambiguous\n",
210 timeres);
211
212 reinit_completion(&dht11->completion);
213
214 dht11->num_edges = 0;
215 ret = gpiod_direction_output(dht11->gpiod, 0);
216 if (ret)
217 goto err;
218 usleep_range(DHT11_START_TRANSMISSION_MIN,
219 DHT11_START_TRANSMISSION_MAX);
220 ret = gpiod_direction_input(dht11->gpiod);
221 if (ret)
222 goto err;
223
224 ret = request_irq(dht11->irq, dht11_handle_irq,
225 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
226 iio_dev->name, iio_dev);
227 if (ret)
228 goto err;
229
230 ret = wait_for_completion_killable_timeout(&dht11->completion,
231 HZ);
232
233 free_irq(dht11->irq, iio_dev);
234
235 #ifdef CONFIG_DYNAMIC_DEBUG
236 dht11_edges_print(dht11);
237 #endif
238
239 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
240 dev_err(dht11->dev, "Only %d signal edges detected\n",
241 dht11->num_edges);
242 ret = -ETIMEDOUT;
243 }
244 if (ret < 0)
245 goto err;
246
247 offset = DHT11_EDGES_PREAMBLE +
248 dht11->num_edges - DHT11_EDGES_PER_READ;
249 for (; offset >= 0; --offset) {
250 ret = dht11_decode(dht11, offset);
251 if (!ret)
252 break;
253 }
254
255 if (ret)
256 goto err;
257 }
258
259 ret = IIO_VAL_INT;
260 if (chan->type == IIO_TEMP)
261 *val = dht11->temperature;
262 else if (chan->type == IIO_HUMIDITYRELATIVE)
263 *val = dht11->humidity;
264 else
265 ret = -EINVAL;
266 err:
267 dht11->num_edges = -1;
268 mutex_unlock(&dht11->lock);
269 return ret;
270 }
271
272 static const struct iio_info dht11_iio_info = {
273 .read_raw = dht11_read_raw,
274 };
275
276 static const struct iio_chan_spec dht11_chan_spec[] = {
277 { .type = IIO_TEMP,
278 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
279 { .type = IIO_HUMIDITYRELATIVE,
280 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
281 };
282
283 static const struct of_device_id dht11_dt_ids[] = {
284 { .compatible = "dht11", },
285 { }
286 };
287 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
288
dht11_probe(struct platform_device * pdev)289 static int dht11_probe(struct platform_device *pdev)
290 {
291 struct device *dev = &pdev->dev;
292 struct dht11 *dht11;
293 struct iio_dev *iio;
294
295 iio = devm_iio_device_alloc(dev, sizeof(*dht11));
296 if (!iio)
297 return -ENOMEM;
298
299 dht11 = iio_priv(iio);
300 dht11->dev = dev;
301 dht11->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN);
302 if (IS_ERR(dht11->gpiod))
303 return PTR_ERR(dht11->gpiod);
304
305 dht11->irq = gpiod_to_irq(dht11->gpiod);
306 if (dht11->irq < 0) {
307 dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod));
308 return -EINVAL;
309 }
310
311 dht11->timestamp = ktime_get_boottime_ns() - DHT11_DATA_VALID_TIME - 1;
312 dht11->num_edges = -1;
313
314 platform_set_drvdata(pdev, iio);
315
316 init_completion(&dht11->completion);
317 mutex_init(&dht11->lock);
318 iio->name = pdev->name;
319 iio->info = &dht11_iio_info;
320 iio->modes = INDIO_DIRECT_MODE;
321 iio->channels = dht11_chan_spec;
322 iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
323
324 return devm_iio_device_register(dev, iio);
325 }
326
327 static struct platform_driver dht11_driver = {
328 .driver = {
329 .name = "dht11",
330 .of_match_table = dht11_dt_ids,
331 },
332 .probe = dht11_probe,
333 };
334
335 module_platform_driver(dht11_driver);
336
337 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
338 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
339 MODULE_LICENSE("GPL v2");
340