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/sysfs.h>
15 #include <linux/io.h>
16 #include <linux/mod_devicetable.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 DRIVER_NAME "dht11"
30
31 #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */
32
33 #define DHT11_EDGES_PREAMBLE 2
34 #define DHT11_BITS_PER_READ 40
35 /*
36 * Note that when reading the sensor actually 84 edges are detected, but
37 * since the last edge is not significant, we only store 83:
38 */
39 #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \
40 DHT11_EDGES_PREAMBLE + 1)
41
42 /*
43 * Data transmission timing:
44 * Data bits are encoded as pulse length (high time) on the data line.
45 * 0-bit: 22-30uS -- typically 26uS (AM2302)
46 * 1-bit: 68-75uS -- typically 70uS (AM2302)
47 * The acutal timings also depend on the properties of the cable, with
48 * longer cables typically making pulses shorter.
49 *
50 * Our decoding depends on the time resolution of the system:
51 * timeres > 34uS ... don't know what a 1-tick pulse is
52 * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks)
53 * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is
54 * timeres < 23uS ... no problem
55 *
56 * Luckily clocks in the 33-44kHz range are quite uncommon, so we can
57 * support most systems if the threshold for decoding a pulse as 1-bit
58 * is chosen carefully. If somebody really wants to support clocks around
59 * 40kHz, where this driver is most unreliable, there are two options.
60 * a) select an implementation using busy loop polling on those systems
61 * b) use the checksum to do some probabilistic decoding
62 */
63 #define DHT11_START_TRANSMISSION_MIN 18000 /* us */
64 #define DHT11_START_TRANSMISSION_MAX 20000 /* us */
65 #define DHT11_MIN_TIMERES 34000 /* ns */
66 #define DHT11_THRESHOLD 49000 /* ns */
67 #define DHT11_AMBIG_LOW 23000 /* ns */
68 #define DHT11_AMBIG_HIGH 30000 /* ns */
69
70 struct dht11 {
71 struct device *dev;
72
73 struct gpio_desc *gpiod;
74 int irq;
75
76 struct completion completion;
77 /* The iio sysfs interface doesn't prevent concurrent reads: */
78 struct mutex lock;
79
80 s64 timestamp;
81 int temperature;
82 int humidity;
83
84 /* num_edges: -1 means "no transmission in progress" */
85 int num_edges;
86 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ];
87 };
88
89 #ifdef CONFIG_DYNAMIC_DEBUG
90 /*
91 * dht11_edges_print: show the data as actually received by the
92 * driver.
93 */
dht11_edges_print(struct dht11 * dht11)94 static void dht11_edges_print(struct dht11 *dht11)
95 {
96 int i;
97
98 dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);
99 for (i = 1; i < dht11->num_edges; ++i) {
100 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
101 dht11->edges[i].ts - dht11->edges[i - 1].ts,
102 dht11->edges[i - 1].value ? "high" : "low");
103 }
104 }
105 #endif /* CONFIG_DYNAMIC_DEBUG */
106
dht11_decode_byte(char * bits)107 static unsigned char dht11_decode_byte(char *bits)
108 {
109 unsigned char ret = 0;
110 int i;
111
112 for (i = 0; i < 8; ++i) {
113 ret <<= 1;
114 if (bits[i])
115 ++ret;
116 }
117
118 return ret;
119 }
120
dht11_decode(struct dht11 * dht11,int offset)121 static int dht11_decode(struct dht11 *dht11, int offset)
122 {
123 int i, t;
124 char bits[DHT11_BITS_PER_READ];
125 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
126
127 for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
128 t = dht11->edges[offset + 2 * i + 2].ts -
129 dht11->edges[offset + 2 * i + 1].ts;
130 if (!dht11->edges[offset + 2 * i + 1].value) {
131 dev_dbg(dht11->dev,
132 "lost synchronisation at edge %d\n",
133 offset + 2 * i + 1);
134 return -EIO;
135 }
136 bits[i] = t > DHT11_THRESHOLD;
137 }
138
139 hum_int = dht11_decode_byte(bits);
140 hum_dec = dht11_decode_byte(&bits[8]);
141 temp_int = dht11_decode_byte(&bits[16]);
142 temp_dec = dht11_decode_byte(&bits[24]);
143 checksum = dht11_decode_byte(&bits[32]);
144
145 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {
146 dev_dbg(dht11->dev, "invalid checksum\n");
147 return -EIO;
148 }
149
150 dht11->timestamp = ktime_get_boottime_ns();
151 if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */
152 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
153 ((temp_int & 0x80) ? -100 : 100);
154 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
155 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */
156 dht11->temperature = temp_int * 1000;
157 dht11->humidity = hum_int * 1000;
158 } else {
159 dev_err(dht11->dev,
160 "Don't know how to decode data: %d %d %d %d\n",
161 hum_int, hum_dec, temp_int, temp_dec);
162 return -EIO;
163 }
164
165 return 0;
166 }
167
168 /*
169 * IRQ handler called on GPIO edges
170 */
dht11_handle_irq(int irq,void * data)171 static irqreturn_t dht11_handle_irq(int irq, void *data)
172 {
173 struct iio_dev *iio = data;
174 struct dht11 *dht11 = iio_priv(iio);
175
176 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
177 dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns();
178 dht11->edges[dht11->num_edges++].value =
179 gpiod_get_value(dht11->gpiod);
180
181 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
182 complete(&dht11->completion);
183 }
184
185 return IRQ_HANDLED;
186 }
187
dht11_read_raw(struct iio_dev * iio_dev,const struct iio_chan_spec * chan,int * val,int * val2,long m)188 static int dht11_read_raw(struct iio_dev *iio_dev,
189 const struct iio_chan_spec *chan,
190 int *val, int *val2, long m)
191 {
192 struct dht11 *dht11 = iio_priv(iio_dev);
193 int ret, timeres, offset;
194
195 mutex_lock(&dht11->lock);
196 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boottime_ns()) {
197 timeres = ktime_get_resolution_ns();
198 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);
199 if (timeres > DHT11_MIN_TIMERES) {
200 dev_err(dht11->dev, "timeresolution %dns too low\n",
201 timeres);
202 /* In theory a better clock could become available
203 * at some point ... and there is no error code
204 * that really fits better.
205 */
206 ret = -EAGAIN;
207 goto err;
208 }
209 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)
210 dev_warn(dht11->dev,
211 "timeresolution: %dns - decoding ambiguous\n",
212 timeres);
213
214 reinit_completion(&dht11->completion);
215
216 dht11->num_edges = 0;
217 ret = gpiod_direction_output(dht11->gpiod, 0);
218 if (ret)
219 goto err;
220 usleep_range(DHT11_START_TRANSMISSION_MIN,
221 DHT11_START_TRANSMISSION_MAX);
222 ret = gpiod_direction_input(dht11->gpiod);
223 if (ret)
224 goto err;
225
226 ret = request_irq(dht11->irq, dht11_handle_irq,
227 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
228 iio_dev->name, iio_dev);
229 if (ret)
230 goto err;
231
232 ret = wait_for_completion_killable_timeout(&dht11->completion,
233 HZ);
234
235 free_irq(dht11->irq, iio_dev);
236
237 #ifdef CONFIG_DYNAMIC_DEBUG
238 dht11_edges_print(dht11);
239 #endif
240
241 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
242 dev_err(dht11->dev, "Only %d signal edges detected\n",
243 dht11->num_edges);
244 ret = -ETIMEDOUT;
245 }
246 if (ret < 0)
247 goto err;
248
249 offset = DHT11_EDGES_PREAMBLE +
250 dht11->num_edges - DHT11_EDGES_PER_READ;
251 for (; offset >= 0; --offset) {
252 ret = dht11_decode(dht11, offset);
253 if (!ret)
254 break;
255 }
256
257 if (ret)
258 goto err;
259 }
260
261 ret = IIO_VAL_INT;
262 if (chan->type == IIO_TEMP)
263 *val = dht11->temperature;
264 else if (chan->type == IIO_HUMIDITYRELATIVE)
265 *val = dht11->humidity;
266 else
267 ret = -EINVAL;
268 err:
269 dht11->num_edges = -1;
270 mutex_unlock(&dht11->lock);
271 return ret;
272 }
273
274 static const struct iio_info dht11_iio_info = {
275 .read_raw = dht11_read_raw,
276 };
277
278 static const struct iio_chan_spec dht11_chan_spec[] = {
279 { .type = IIO_TEMP,
280 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
281 { .type = IIO_HUMIDITYRELATIVE,
282 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
283 };
284
285 static const struct of_device_id dht11_dt_ids[] = {
286 { .compatible = "dht11", },
287 { }
288 };
289 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
290
dht11_probe(struct platform_device * pdev)291 static int dht11_probe(struct platform_device *pdev)
292 {
293 struct device *dev = &pdev->dev;
294 struct dht11 *dht11;
295 struct iio_dev *iio;
296
297 iio = devm_iio_device_alloc(dev, sizeof(*dht11));
298 if (!iio) {
299 dev_err(dev, "Failed to allocate IIO device\n");
300 return -ENOMEM;
301 }
302
303 dht11 = iio_priv(iio);
304 dht11->dev = dev;
305 dht11->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN);
306 if (IS_ERR(dht11->gpiod))
307 return PTR_ERR(dht11->gpiod);
308
309 dht11->irq = gpiod_to_irq(dht11->gpiod);
310 if (dht11->irq < 0) {
311 dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod));
312 return -EINVAL;
313 }
314
315 dht11->timestamp = ktime_get_boottime_ns() - DHT11_DATA_VALID_TIME - 1;
316 dht11->num_edges = -1;
317
318 platform_set_drvdata(pdev, iio);
319
320 init_completion(&dht11->completion);
321 mutex_init(&dht11->lock);
322 iio->name = pdev->name;
323 iio->info = &dht11_iio_info;
324 iio->modes = INDIO_DIRECT_MODE;
325 iio->channels = dht11_chan_spec;
326 iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
327
328 return devm_iio_device_register(dev, iio);
329 }
330
331 static struct platform_driver dht11_driver = {
332 .driver = {
333 .name = DRIVER_NAME,
334 .of_match_table = dht11_dt_ids,
335 },
336 .probe = dht11_probe,
337 };
338
339 module_platform_driver(dht11_driver);
340
341 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
342 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
343 MODULE_LICENSE("GPL v2");
344
