treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157
[sfrench/cifs-2.6.git] / drivers / iio / humidity / dht11.c
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/of.h>
15 #include <linux/of_device.h>
16 #include <linux/sysfs.h>
17 #include <linux/io.h>
18 #include <linux/module.h>
19 #include <linux/platform_device.h>
20 #include <linux/wait.h>
21 #include <linux/bitops.h>
22 #include <linux/completion.h>
23 #include <linux/mutex.h>
24 #include <linux/delay.h>
25 #include <linux/gpio.h>
26 #include <linux/of_gpio.h>
27 #include <linux/timekeeping.h>
28
29 #include <linux/iio/iio.h>
30
31 #define DRIVER_NAME     "dht11"
32
33 #define DHT11_DATA_VALID_TIME   2000000000  /* 2s in ns */
34
35 #define DHT11_EDGES_PREAMBLE 2
36 #define DHT11_BITS_PER_READ 40
37 /*
38  * Note that when reading the sensor actually 84 edges are detected, but
39  * since the last edge is not significant, we only store 83:
40  */
41 #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \
42                               DHT11_EDGES_PREAMBLE + 1)
43
44 /*
45  * Data transmission timing:
46  * Data bits are encoded as pulse length (high time) on the data line.
47  * 0-bit: 22-30uS -- typically 26uS (AM2302)
48  * 1-bit: 68-75uS -- typically 70uS (AM2302)
49  * The acutal timings also depend on the properties of the cable, with
50  * longer cables typically making pulses shorter.
51  *
52  * Our decoding depends on the time resolution of the system:
53  * timeres > 34uS ... don't know what a 1-tick pulse is
54  * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks)
55  * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is
56  * timeres < 23uS ... no problem
57  *
58  * Luckily clocks in the 33-44kHz range are quite uncommon, so we can
59  * support most systems if the threshold for decoding a pulse as 1-bit
60  * is chosen carefully. If somebody really wants to support clocks around
61  * 40kHz, where this driver is most unreliable, there are two options.
62  * a) select an implementation using busy loop polling on those systems
63  * b) use the checksum to do some probabilistic decoding
64  */
65 #define DHT11_START_TRANSMISSION_MIN    18000  /* us */
66 #define DHT11_START_TRANSMISSION_MAX    20000  /* us */
67 #define DHT11_MIN_TIMERES       34000  /* ns */
68 #define DHT11_THRESHOLD         49000  /* ns */
69 #define DHT11_AMBIG_LOW         23000  /* ns */
70 #define DHT11_AMBIG_HIGH        30000  /* ns */
71
72 struct dht11 {
73         struct device                   *dev;
74
75         int                             gpio;
76         int                             irq;
77
78         struct completion               completion;
79         /* The iio sysfs interface doesn't prevent concurrent reads: */
80         struct mutex                    lock;
81
82         s64                             timestamp;
83         int                             temperature;
84         int                             humidity;
85
86         /* num_edges: -1 means "no transmission in progress" */
87         int                             num_edges;
88         struct {s64 ts; int value; }    edges[DHT11_EDGES_PER_READ];
89 };
90
91 #ifdef CONFIG_DYNAMIC_DEBUG
92 /*
93  * dht11_edges_print: show the data as actually received by the
94  *                    driver.
95  */
96 static void dht11_edges_print(struct dht11 *dht11)
97 {
98         int i;
99
100         dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);
101         for (i = 1; i < dht11->num_edges; ++i) {
102                 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
103                         dht11->edges[i].ts - dht11->edges[i - 1].ts,
104                         dht11->edges[i - 1].value ? "high" : "low");
105         }
106 }
107 #endif /* CONFIG_DYNAMIC_DEBUG */
108
109 static unsigned char dht11_decode_byte(char *bits)
110 {
111         unsigned char ret = 0;
112         int i;
113
114         for (i = 0; i < 8; ++i) {
115                 ret <<= 1;
116                 if (bits[i])
117                         ++ret;
118         }
119
120         return ret;
121 }
122
123 static int dht11_decode(struct dht11 *dht11, int offset)
124 {
125         int i, t;
126         char bits[DHT11_BITS_PER_READ];
127         unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
128
129         for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
130                 t = dht11->edges[offset + 2 * i + 2].ts -
131                         dht11->edges[offset + 2 * i + 1].ts;
132                 if (!dht11->edges[offset + 2 * i + 1].value) {
133                         dev_dbg(dht11->dev,
134                                 "lost synchronisation at edge %d\n",
135                                 offset + 2 * i + 1);
136                         return -EIO;
137                 }
138                 bits[i] = t > DHT11_THRESHOLD;
139         }
140
141         hum_int = dht11_decode_byte(bits);
142         hum_dec = dht11_decode_byte(&bits[8]);
143         temp_int = dht11_decode_byte(&bits[16]);
144         temp_dec = dht11_decode_byte(&bits[24]);
145         checksum = dht11_decode_byte(&bits[32]);
146
147         if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {
148                 dev_dbg(dht11->dev, "invalid checksum\n");
149                 return -EIO;
150         }
151
152         dht11->timestamp = ktime_get_boot_ns();
153         if (hum_int < 4) {  /* DHT22: 100000 = (3*256+232)*100 */
154                 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
155                                         ((temp_int & 0x80) ? -100 : 100);
156                 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
157         } else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
158                 dht11->temperature = temp_int * 1000;
159                 dht11->humidity = hum_int * 1000;
160         } else {
161                 dev_err(dht11->dev,
162                         "Don't know how to decode data: %d %d %d %d\n",
163                         hum_int, hum_dec, temp_int, temp_dec);
164                 return -EIO;
165         }
166
167         return 0;
168 }
169
170 /*
171  * IRQ handler called on GPIO edges
172  */
173 static irqreturn_t dht11_handle_irq(int irq, void *data)
174 {
175         struct iio_dev *iio = data;
176         struct dht11 *dht11 = iio_priv(iio);
177
178         /* TODO: Consider making the handler safe for IRQ sharing */
179         if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
180                 dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns();
181                 dht11->edges[dht11->num_edges++].value =
182                                                 gpio_get_value(dht11->gpio);
183
184                 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
185                         complete(&dht11->completion);
186         }
187
188         return IRQ_HANDLED;
189 }
190
191 static int dht11_read_raw(struct iio_dev *iio_dev,
192                           const struct iio_chan_spec *chan,
193                         int *val, int *val2, long m)
194 {
195         struct dht11 *dht11 = iio_priv(iio_dev);
196         int ret, timeres, offset;
197
198         mutex_lock(&dht11->lock);
199         if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) {
200                 timeres = ktime_get_resolution_ns();
201                 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);
202                 if (timeres > DHT11_MIN_TIMERES) {
203                         dev_err(dht11->dev, "timeresolution %dns too low\n",
204                                 timeres);
205                         /* In theory a better clock could become available
206                          * at some point ... and there is no error code
207                          * that really fits better.
208                          */
209                         ret = -EAGAIN;
210                         goto err;
211                 }
212                 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)
213                         dev_warn(dht11->dev,
214                                  "timeresolution: %dns - decoding ambiguous\n",
215                                  timeres);
216
217                 reinit_completion(&dht11->completion);
218
219                 dht11->num_edges = 0;
220                 ret = gpio_direction_output(dht11->gpio, 0);
221                 if (ret)
222                         goto err;
223                 usleep_range(DHT11_START_TRANSMISSION_MIN,
224                              DHT11_START_TRANSMISSION_MAX);
225                 ret = gpio_direction_input(dht11->gpio);
226                 if (ret)
227                         goto err;
228
229                 ret = request_irq(dht11->irq, dht11_handle_irq,
230                                   IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
231                                   iio_dev->name, iio_dev);
232                 if (ret)
233                         goto err;
234
235                 ret = wait_for_completion_killable_timeout(&dht11->completion,
236                                                            HZ);
237
238                 free_irq(dht11->irq, iio_dev);
239
240 #ifdef CONFIG_DYNAMIC_DEBUG
241                 dht11_edges_print(dht11);
242 #endif
243
244                 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
245                         dev_err(dht11->dev, "Only %d signal edges detected\n",
246                                 dht11->num_edges);
247                         ret = -ETIMEDOUT;
248                 }
249                 if (ret < 0)
250                         goto err;
251
252                 offset = DHT11_EDGES_PREAMBLE +
253                                 dht11->num_edges - DHT11_EDGES_PER_READ;
254                 for (; offset >= 0; --offset) {
255                         ret = dht11_decode(dht11, offset);
256                         if (!ret)
257                                 break;
258                 }
259
260                 if (ret)
261                         goto err;
262         }
263
264         ret = IIO_VAL_INT;
265         if (chan->type == IIO_TEMP)
266                 *val = dht11->temperature;
267         else if (chan->type == IIO_HUMIDITYRELATIVE)
268                 *val = dht11->humidity;
269         else
270                 ret = -EINVAL;
271 err:
272         dht11->num_edges = -1;
273         mutex_unlock(&dht11->lock);
274         return ret;
275 }
276
277 static const struct iio_info dht11_iio_info = {
278         .read_raw               = dht11_read_raw,
279 };
280
281 static const struct iio_chan_spec dht11_chan_spec[] = {
282         { .type = IIO_TEMP,
283                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
284         { .type = IIO_HUMIDITYRELATIVE,
285                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
286 };
287
288 static const struct of_device_id dht11_dt_ids[] = {
289         { .compatible = "dht11", },
290         { }
291 };
292 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
293
294 static int dht11_probe(struct platform_device *pdev)
295 {
296         struct device *dev = &pdev->dev;
297         struct device_node *node = dev->of_node;
298         struct dht11 *dht11;
299         struct iio_dev *iio;
300         int ret;
301
302         iio = devm_iio_device_alloc(dev, sizeof(*dht11));
303         if (!iio) {
304                 dev_err(dev, "Failed to allocate IIO device\n");
305                 return -ENOMEM;
306         }
307
308         dht11 = iio_priv(iio);
309         dht11->dev = dev;
310
311         ret = of_get_gpio(node, 0);
312         if (ret < 0)
313                 return ret;
314         dht11->gpio = ret;
315         ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
316         if (ret)
317                 return ret;
318
319         dht11->irq = gpio_to_irq(dht11->gpio);
320         if (dht11->irq < 0) {
321                 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
322                 return -EINVAL;
323         }
324
325         dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1;
326         dht11->num_edges = -1;
327
328         platform_set_drvdata(pdev, iio);
329
330         init_completion(&dht11->completion);
331         mutex_init(&dht11->lock);
332         iio->name = pdev->name;
333         iio->dev.parent = &pdev->dev;
334         iio->info = &dht11_iio_info;
335         iio->modes = INDIO_DIRECT_MODE;
336         iio->channels = dht11_chan_spec;
337         iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
338
339         return devm_iio_device_register(dev, iio);
340 }
341
342 static struct platform_driver dht11_driver = {
343         .driver = {
344                 .name   = DRIVER_NAME,
345                 .of_match_table = dht11_dt_ids,
346         },
347         .probe  = dht11_probe,
348 };
349
350 module_platform_driver(dht11_driver);
351
352 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
353 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
354 MODULE_LICENSE("GPL v2");