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1/*
2 * DHT11/DHT22 bit banging GPIO driver
3 *
4 * Copyright (c) Harald Geyer <harald@ccbib.org>
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 */
16
17#include <linux/err.h>
18#include <linux/interrupt.h>
19#include <linux/device.h>
20#include <linux/kernel.h>
21#include <linux/printk.h>
22#include <linux/slab.h>
23#include <linux/of.h>
24#include <linux/of_device.h>
25#include <linux/sysfs.h>
26#include <linux/io.h>
27#include <linux/module.h>
28#include <linux/platform_device.h>
29#include <linux/wait.h>
30#include <linux/bitops.h>
31#include <linux/completion.h>
32#include <linux/mutex.h>
33#include <linux/delay.h>
34#include <linux/gpio.h>
35#include <linux/of_gpio.h>
36#include <linux/timekeeping.h>
37
38#include <linux/iio/iio.h>
39
40#define DRIVER_NAME "dht11"
41
42#define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */
43
44#define DHT11_EDGES_PREAMBLE 2
45#define DHT11_BITS_PER_READ 40
46/*
47 * Note that when reading the sensor actually 84 edges are detected, but
48 * since the last edge is not significant, we only store 83:
49 */
50#define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \
51 DHT11_EDGES_PREAMBLE + 1)
52
53/*
54 * Data transmission timing:
55 * Data bits are encoded as pulse length (high time) on the data line.
56 * 0-bit: 22-30uS -- typically 26uS (AM2302)
57 * 1-bit: 68-75uS -- typically 70uS (AM2302)
58 * The acutal timings also depend on the properties of the cable, with
59 * longer cables typically making pulses shorter.
60 *
61 * Our decoding depends on the time resolution of the system:
62 * timeres > 34uS ... don't know what a 1-tick pulse is
63 * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks)
64 * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is
65 * timeres < 23uS ... no problem
66 *
67 * Luckily clocks in the 33-44kHz range are quite uncommon, so we can
68 * support most systems if the threshold for decoding a pulse as 1-bit
69 * is chosen carefully. If somebody really wants to support clocks around
70 * 40kHz, where this driver is most unreliable, there are two options.
71 * a) select an implementation using busy loop polling on those systems
72 * b) use the checksum to do some probabilistic decoding
73 */
74#define DHT11_START_TRANSMISSION_MIN 18000 /* us */
75#define DHT11_START_TRANSMISSION_MAX 20000 /* us */
76#define DHT11_MIN_TIMERES 34000 /* ns */
77#define DHT11_THRESHOLD 49000 /* ns */
78#define DHT11_AMBIG_LOW 23000 /* ns */
79#define DHT11_AMBIG_HIGH 30000 /* ns */
80
81struct dht11 {
82 struct device *dev;
83
84 int gpio;
85 int irq;
86
87 struct completion completion;
88 /* The iio sysfs interface doesn't prevent concurrent reads: */
89 struct mutex lock;
90
91 s64 timestamp;
92 int temperature;
93 int humidity;
94
95 /* num_edges: -1 means "no transmission in progress" */
96 int num_edges;
97 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ];
98};
99
100#ifdef CONFIG_DYNAMIC_DEBUG
101/*
102 * dht11_edges_print: show the data as actually received by the
103 * driver.
104 */
105static void dht11_edges_print(struct dht11 *dht11)
106{
107 int i;
108
109 dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);
110 for (i = 1; i < dht11->num_edges; ++i) {
111 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
112 dht11->edges[i].ts - dht11->edges[i - 1].ts,
113 dht11->edges[i - 1].value ? "high" : "low");
114 }
115}
116#endif /* CONFIG_DYNAMIC_DEBUG */
117
118static unsigned char dht11_decode_byte(char *bits)
119{
120 unsigned char ret = 0;
121 int i;
122
123 for (i = 0; i < 8; ++i) {
124 ret <<= 1;
125 if (bits[i])
126 ++ret;
127 }
128
129 return ret;
130}
131
132static int dht11_decode(struct dht11 *dht11, int offset)
133{
134 int i, t;
135 char bits[DHT11_BITS_PER_READ];
136 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
137
138 for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
139 t = dht11->edges[offset + 2 * i + 2].ts -
140 dht11->edges[offset + 2 * i + 1].ts;
141 if (!dht11->edges[offset + 2 * i + 1].value) {
142 dev_dbg(dht11->dev,
143 "lost synchronisation at edge %d\n",
144 offset + 2 * i + 1);
145 return -EIO;
146 }
147 bits[i] = t > DHT11_THRESHOLD;
148 }
149
150 hum_int = dht11_decode_byte(bits);
151 hum_dec = dht11_decode_byte(&bits[8]);
152 temp_int = dht11_decode_byte(&bits[16]);
153 temp_dec = dht11_decode_byte(&bits[24]);
154 checksum = dht11_decode_byte(&bits[32]);
155
156 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {
157 dev_dbg(dht11->dev, "invalid checksum\n");
158 return -EIO;
159 }
160
161 dht11->timestamp = ktime_get_boot_ns();
162 if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */
163 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
164 ((temp_int & 0x80) ? -100 : 100);
165 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
166 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */
167 dht11->temperature = temp_int * 1000;
168 dht11->humidity = hum_int * 1000;
169 } else {
170 dev_err(dht11->dev,
171 "Don't know how to decode data: %d %d %d %d\n",
172 hum_int, hum_dec, temp_int, temp_dec);
173 return -EIO;
174 }
175
176 return 0;
177}
178
179/*
180 * IRQ handler called on GPIO edges
181 */
182static irqreturn_t dht11_handle_irq(int irq, void *data)
183{
184 struct iio_dev *iio = data;
185 struct dht11 *dht11 = iio_priv(iio);
186
187 /* TODO: Consider making the handler safe for IRQ sharing */
188 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
189 dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns();
190 dht11->edges[dht11->num_edges++].value =
191 gpio_get_value(dht11->gpio);
192
193 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
194 complete(&dht11->completion);
195 }
196
197 return IRQ_HANDLED;
198}
199
200static int dht11_read_raw(struct iio_dev *iio_dev,
201 const struct iio_chan_spec *chan,
202 int *val, int *val2, long m)
203{
204 struct dht11 *dht11 = iio_priv(iio_dev);
205 int ret, timeres, offset;
206
207 mutex_lock(&dht11->lock);
208 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) {
209 timeres = ktime_get_resolution_ns();
210 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);
211 if (timeres > DHT11_MIN_TIMERES) {
212 dev_err(dht11->dev, "timeresolution %dns too low\n",
213 timeres);
214 /* In theory a better clock could become available
215 * at some point ... and there is no error code
216 * that really fits better.
217 */
218 ret = -EAGAIN;
219 goto err;
220 }
221 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)
222 dev_warn(dht11->dev,
223 "timeresolution: %dns - decoding ambiguous\n",
224 timeres);
225
226 reinit_completion(&dht11->completion);
227
228 dht11->num_edges = 0;
229 ret = gpio_direction_output(dht11->gpio, 0);
230 if (ret)
231 goto err;
232 usleep_range(DHT11_START_TRANSMISSION_MIN,
233 DHT11_START_TRANSMISSION_MAX);
234 ret = gpio_direction_input(dht11->gpio);
235 if (ret)
236 goto err;
237
238 ret = request_irq(dht11->irq, dht11_handle_irq,
239 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
240 iio_dev->name, iio_dev);
241 if (ret)
242 goto err;
243
244 ret = wait_for_completion_killable_timeout(&dht11->completion,
245 HZ);
246
247 free_irq(dht11->irq, iio_dev);
248
249#ifdef CONFIG_DYNAMIC_DEBUG
250 dht11_edges_print(dht11);
251#endif
252
253 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
254 dev_err(dht11->dev, "Only %d signal edges detected\n",
255 dht11->num_edges);
256 ret = -ETIMEDOUT;
257 }
258 if (ret < 0)
259 goto err;
260
261 offset = DHT11_EDGES_PREAMBLE +
262 dht11->num_edges - DHT11_EDGES_PER_READ;
263 for (; offset >= 0; --offset) {
264 ret = dht11_decode(dht11, offset);
265 if (!ret)
266 break;
267 }
268
269 if (ret)
270 goto err;
271 }
272
273 ret = IIO_VAL_INT;
274 if (chan->type == IIO_TEMP)
275 *val = dht11->temperature;
276 else if (chan->type == IIO_HUMIDITYRELATIVE)
277 *val = dht11->humidity;
278 else
279 ret = -EINVAL;
280err:
281 dht11->num_edges = -1;
282 mutex_unlock(&dht11->lock);
283 return ret;
284}
285
286static const struct iio_info dht11_iio_info = {
287 .read_raw = dht11_read_raw,
288};
289
290static const struct iio_chan_spec dht11_chan_spec[] = {
291 { .type = IIO_TEMP,
292 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
293 { .type = IIO_HUMIDITYRELATIVE,
294 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
295};
296
297static const struct of_device_id dht11_dt_ids[] = {
298 { .compatible = "dht11", },
299 { }
300};
301MODULE_DEVICE_TABLE(of, dht11_dt_ids);
302
303static int dht11_probe(struct platform_device *pdev)
304{
305 struct device *dev = &pdev->dev;
306 struct device_node *node = dev->of_node;
307 struct dht11 *dht11;
308 struct iio_dev *iio;
309 int ret;
310
311 iio = devm_iio_device_alloc(dev, sizeof(*dht11));
312 if (!iio) {
313 dev_err(dev, "Failed to allocate IIO device\n");
314 return -ENOMEM;
315 }
316
317 dht11 = iio_priv(iio);
318 dht11->dev = dev;
319
320 ret = of_get_gpio(node, 0);
321 if (ret < 0)
322 return ret;
323 dht11->gpio = ret;
324 ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
325 if (ret)
326 return ret;
327
328 dht11->irq = gpio_to_irq(dht11->gpio);
329 if (dht11->irq < 0) {
330 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
331 return -EINVAL;
332 }
333
334 dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1;
335 dht11->num_edges = -1;
336
337 platform_set_drvdata(pdev, iio);
338
339 init_completion(&dht11->completion);
340 mutex_init(&dht11->lock);
341 iio->name = pdev->name;
342 iio->dev.parent = &pdev->dev;
343 iio->info = &dht11_iio_info;
344 iio->modes = INDIO_DIRECT_MODE;
345 iio->channels = dht11_chan_spec;
346 iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
347
348 return devm_iio_device_register(dev, iio);
349}
350
351static struct platform_driver dht11_driver = {
352 .driver = {
353 .name = DRIVER_NAME,
354 .of_match_table = dht11_dt_ids,
355 },
356 .probe = dht11_probe,
357};
358
359module_platform_driver(dht11_driver);
360
361MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
362MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
363MODULE_LICENSE("GPL v2");