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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/consumer.h>
26#include <linux/timekeeping.h>
27
28#include <linux/iio/iio.h>
29
30#define DRIVER_NAME "dht11"
31
32#define DHT11_DATA_VALID_TIME 2000000000
33
34#define DHT11_EDGES_PREAMBLE 2
35#define DHT11_BITS_PER_READ 40
36
37
38
39
40#define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \
41 DHT11_EDGES_PREAMBLE + 1)
42
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63
64#define DHT11_START_TRANSMISSION_MIN 18000
65#define DHT11_START_TRANSMISSION_MAX 20000
66#define DHT11_MIN_TIMERES 34000
67#define DHT11_THRESHOLD 49000
68#define DHT11_AMBIG_LOW 23000
69#define DHT11_AMBIG_HIGH 30000
70
71struct dht11 {
72 struct device *dev;
73
74 struct gpio_desc *gpiod;
75 int irq;
76
77 struct completion completion;
78
79 struct mutex lock;
80
81 s64 timestamp;
82 int temperature;
83 int humidity;
84
85
86 int num_edges;
87 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ];
88};
89
90#ifdef CONFIG_DYNAMIC_DEBUG
91
92
93
94
95static void dht11_edges_print(struct dht11 *dht11)
96{
97 int i;
98
99 dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);
100 for (i = 1; i < dht11->num_edges; ++i) {
101 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
102 dht11->edges[i].ts - dht11->edges[i - 1].ts,
103 dht11->edges[i - 1].value ? "high" : "low");
104 }
105}
106#endif
107
108static unsigned char dht11_decode_byte(char *bits)
109{
110 unsigned char ret = 0;
111 int i;
112
113 for (i = 0; i < 8; ++i) {
114 ret <<= 1;
115 if (bits[i])
116 ++ret;
117 }
118
119 return ret;
120}
121
122static int dht11_decode(struct dht11 *dht11, int offset)
123{
124 int i, t;
125 char bits[DHT11_BITS_PER_READ];
126 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
127
128 for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
129 t = dht11->edges[offset + 2 * i + 2].ts -
130 dht11->edges[offset + 2 * i + 1].ts;
131 if (!dht11->edges[offset + 2 * i + 1].value) {
132 dev_dbg(dht11->dev,
133 "lost synchronisation at edge %d\n",
134 offset + 2 * i + 1);
135 return -EIO;
136 }
137 bits[i] = t > DHT11_THRESHOLD;
138 }
139
140 hum_int = dht11_decode_byte(bits);
141 hum_dec = dht11_decode_byte(&bits[8]);
142 temp_int = dht11_decode_byte(&bits[16]);
143 temp_dec = dht11_decode_byte(&bits[24]);
144 checksum = dht11_decode_byte(&bits[32]);
145
146 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {
147 dev_dbg(dht11->dev, "invalid checksum\n");
148 return -EIO;
149 }
150
151 dht11->timestamp = ktime_get_boottime_ns();
152 if (hum_int < 4) {
153 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
154 ((temp_int & 0x80) ? -100 : 100);
155 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
156 } else if (temp_dec == 0 && hum_dec == 0) {
157 dht11->temperature = temp_int * 1000;
158 dht11->humidity = hum_int * 1000;
159 } else {
160 dev_err(dht11->dev,
161 "Don't know how to decode data: %d %d %d %d\n",
162 hum_int, hum_dec, temp_int, temp_dec);
163 return -EIO;
164 }
165
166 return 0;
167}
168
169
170
171
172static irqreturn_t dht11_handle_irq(int irq, void *data)
173{
174 struct iio_dev *iio = data;
175 struct dht11 *dht11 = iio_priv(iio);
176
177 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
178 dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns();
179 dht11->edges[dht11->num_edges++].value =
180 gpiod_get_value(dht11->gpiod);
181
182 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
183 complete(&dht11->completion);
184 }
185
186 return IRQ_HANDLED;
187}
188
189static int dht11_read_raw(struct iio_dev *iio_dev,
190 const struct iio_chan_spec *chan,
191 int *val, int *val2, long m)
192{
193 struct dht11 *dht11 = iio_priv(iio_dev);
194 int ret, timeres, offset;
195
196 mutex_lock(&dht11->lock);
197 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boottime_ns()) {
198 timeres = ktime_get_resolution_ns();
199 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);
200 if (timeres > DHT11_MIN_TIMERES) {
201 dev_err(dht11->dev, "timeresolution %dns too low\n",
202 timeres);
203
204
205
206
207 ret = -EAGAIN;
208 goto err;
209 }
210 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)
211 dev_warn(dht11->dev,
212 "timeresolution: %dns - decoding ambiguous\n",
213 timeres);
214
215 reinit_completion(&dht11->completion);
216
217 dht11->num_edges = 0;
218 ret = gpiod_direction_output(dht11->gpiod, 0);
219 if (ret)
220 goto err;
221 usleep_range(DHT11_START_TRANSMISSION_MIN,
222 DHT11_START_TRANSMISSION_MAX);
223 ret = gpiod_direction_input(dht11->gpiod);
224 if (ret)
225 goto err;
226
227 ret = request_irq(dht11->irq, dht11_handle_irq,
228 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
229 iio_dev->name, iio_dev);
230 if (ret)
231 goto err;
232
233 ret = wait_for_completion_killable_timeout(&dht11->completion,
234 HZ);
235
236 free_irq(dht11->irq, iio_dev);
237
238#ifdef CONFIG_DYNAMIC_DEBUG
239 dht11_edges_print(dht11);
240#endif
241
242 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
243 dev_err(dht11->dev, "Only %d signal edges detected\n",
244 dht11->num_edges);
245 ret = -ETIMEDOUT;
246 }
247 if (ret < 0)
248 goto err;
249
250 offset = DHT11_EDGES_PREAMBLE +
251 dht11->num_edges - DHT11_EDGES_PER_READ;
252 for (; offset >= 0; --offset) {
253 ret = dht11_decode(dht11, offset);
254 if (!ret)
255 break;
256 }
257
258 if (ret)
259 goto err;
260 }
261
262 ret = IIO_VAL_INT;
263 if (chan->type == IIO_TEMP)
264 *val = dht11->temperature;
265 else if (chan->type == IIO_HUMIDITYRELATIVE)
266 *val = dht11->humidity;
267 else
268 ret = -EINVAL;
269err:
270 dht11->num_edges = -1;
271 mutex_unlock(&dht11->lock);
272 return ret;
273}
274
275static const struct iio_info dht11_iio_info = {
276 .read_raw = dht11_read_raw,
277};
278
279static const struct iio_chan_spec dht11_chan_spec[] = {
280 { .type = IIO_TEMP,
281 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
282 { .type = IIO_HUMIDITYRELATIVE,
283 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
284};
285
286static const struct of_device_id dht11_dt_ids[] = {
287 { .compatible = "dht11", },
288 { }
289};
290MODULE_DEVICE_TABLE(of, dht11_dt_ids);
291
292static int dht11_probe(struct platform_device *pdev)
293{
294 struct device *dev = &pdev->dev;
295 struct dht11 *dht11;
296 struct iio_dev *iio;
297
298 iio = devm_iio_device_alloc(dev, sizeof(*dht11));
299 if (!iio) {
300 dev_err(dev, "Failed to allocate IIO device\n");
301 return -ENOMEM;
302 }
303
304 dht11 = iio_priv(iio);
305 dht11->dev = dev;
306 dht11->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN);
307 if (IS_ERR(dht11->gpiod))
308 return PTR_ERR(dht11->gpiod);
309
310 dht11->irq = gpiod_to_irq(dht11->gpiod);
311 if (dht11->irq < 0) {
312 dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod));
313 return -EINVAL;
314 }
315
316 dht11->timestamp = ktime_get_boottime_ns() - DHT11_DATA_VALID_TIME - 1;
317 dht11->num_edges = -1;
318
319 platform_set_drvdata(pdev, iio);
320
321 init_completion(&dht11->completion);
322 mutex_init(&dht11->lock);
323 iio->name = pdev->name;
324 iio->info = &dht11_iio_info;
325 iio->modes = INDIO_DIRECT_MODE;
326 iio->channels = dht11_chan_spec;
327 iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
328
329 return devm_iio_device_register(dev, iio);
330}
331
332static struct platform_driver dht11_driver = {
333 .driver = {
334 .name = DRIVER_NAME,
335 .of_match_table = dht11_dt_ids,
336 },
337 .probe = dht11_probe,
338};
339
340module_platform_driver(dht11_driver);
341
342MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
343MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
344MODULE_LICENSE("GPL v2");
345
