Version:  2.0.40 2.2.26 2.4.37 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7

Linux/drivers/iio/humidity/dht11.c

  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        18  /* ms */
 75 #define DHT11_MIN_TIMERES       34000  /* ns */
 76 #define DHT11_THRESHOLD         49000  /* ns */
 77 #define DHT11_AMBIG_LOW         23000  /* ns */
 78 #define DHT11_AMBIG_HIGH        30000  /* ns */
 79 
 80 struct dht11 {
 81         struct device                   *dev;
 82 
 83         int                             gpio;
 84         int                             irq;
 85 
 86         struct completion               completion;
 87         /* The iio sysfs interface doesn't prevent concurrent reads: */
 88         struct mutex                    lock;
 89 
 90         s64                             timestamp;
 91         int                             temperature;
 92         int                             humidity;
 93 
 94         /* num_edges: -1 means "no transmission in progress" */
 95         int                             num_edges;
 96         struct {s64 ts; int value; }    edges[DHT11_EDGES_PER_READ];
 97 };
 98 
 99 #ifdef CONFIG_DYNAMIC_DEBUG
100 /*
101  * dht11_edges_print: show the data as actually received by the
102  *                    driver.
103  */
104 static void dht11_edges_print(struct dht11 *dht11)
105 {
106         int i;
107 
108         dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);
109         for (i = 1; i < dht11->num_edges; ++i) {
110                 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
111                         dht11->edges[i].ts - dht11->edges[i - 1].ts,
112                         dht11->edges[i - 1].value ? "high" : "low");
113         }
114 }
115 #endif /* CONFIG_DYNAMIC_DEBUG */
116 
117 static unsigned char dht11_decode_byte(char *bits)
118 {
119         unsigned char ret = 0;
120         int i;
121 
122         for (i = 0; i < 8; ++i) {
123                 ret <<= 1;
124                 if (bits[i])
125                         ++ret;
126         }
127 
128         return ret;
129 }
130 
131 static int dht11_decode(struct dht11 *dht11, int offset)
132 {
133         int i, t;
134         char bits[DHT11_BITS_PER_READ];
135         unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
136 
137         for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
138                 t = dht11->edges[offset + 2 * i + 2].ts -
139                         dht11->edges[offset + 2 * i + 1].ts;
140                 if (!dht11->edges[offset + 2 * i + 1].value) {
141                         dev_dbg(dht11->dev,
142                                 "lost synchronisation at edge %d\n",
143                                 offset + 2 * i + 1);
144                         return -EIO;
145                 }
146                 bits[i] = t > DHT11_THRESHOLD;
147         }
148 
149         hum_int = dht11_decode_byte(bits);
150         hum_dec = dht11_decode_byte(&bits[8]);
151         temp_int = dht11_decode_byte(&bits[16]);
152         temp_dec = dht11_decode_byte(&bits[24]);
153         checksum = dht11_decode_byte(&bits[32]);
154 
155         if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {
156                 dev_dbg(dht11->dev, "invalid checksum\n");
157                 return -EIO;
158         }
159 
160         dht11->timestamp = ktime_get_boot_ns();
161         if (hum_int < 20) {  /* DHT22 */
162                 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
163                                         ((temp_int & 0x80) ? -100 : 100);
164                 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
165         } else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
166                 dht11->temperature = temp_int * 1000;
167                 dht11->humidity = hum_int * 1000;
168         } else {
169                 dev_err(dht11->dev,
170                         "Don't know how to decode data: %d %d %d %d\n",
171                         hum_int, hum_dec, temp_int, temp_dec);
172                 return -EIO;
173         }
174 
175         return 0;
176 }
177 
178 /*
179  * IRQ handler called on GPIO edges
180  */
181 static irqreturn_t dht11_handle_irq(int irq, void *data)
182 {
183         struct iio_dev *iio = data;
184         struct dht11 *dht11 = iio_priv(iio);
185 
186         /* TODO: Consider making the handler safe for IRQ sharing */
187         if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
188                 dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns();
189                 dht11->edges[dht11->num_edges++].value =
190                                                 gpio_get_value(dht11->gpio);
191 
192                 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
193                         complete(&dht11->completion);
194         }
195 
196         return IRQ_HANDLED;
197 }
198 
199 static int dht11_read_raw(struct iio_dev *iio_dev,
200                           const struct iio_chan_spec *chan,
201                         int *val, int *val2, long m)
202 {
203         struct dht11 *dht11 = iio_priv(iio_dev);
204         int ret, timeres, offset;
205 
206         mutex_lock(&dht11->lock);
207         if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) {
208                 timeres = ktime_get_resolution_ns();
209                 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);
210                 if (timeres > DHT11_MIN_TIMERES) {
211                         dev_err(dht11->dev, "timeresolution %dns too low\n",
212                                 timeres);
213                         /* In theory a better clock could become available
214                          * at some point ... and there is no error code
215                          * that really fits better.
216                          */
217                         ret = -EAGAIN;
218                         goto err;
219                 }
220                 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)
221                         dev_warn(dht11->dev,
222                                  "timeresolution: %dns - decoding ambiguous\n",
223                                  timeres);
224 
225                 reinit_completion(&dht11->completion);
226 
227                 dht11->num_edges = 0;
228                 ret = gpio_direction_output(dht11->gpio, 0);
229                 if (ret)
230                         goto err;
231                 msleep(DHT11_START_TRANSMISSION);
232                 ret = gpio_direction_input(dht11->gpio);
233                 if (ret)
234                         goto err;
235 
236                 ret = request_irq(dht11->irq, dht11_handle_irq,
237                                   IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
238                                   iio_dev->name, iio_dev);
239                 if (ret)
240                         goto err;
241 
242                 ret = wait_for_completion_killable_timeout(&dht11->completion,
243                                                            HZ);
244 
245                 free_irq(dht11->irq, iio_dev);
246 
247 #ifdef CONFIG_DYNAMIC_DEBUG
248                 dht11_edges_print(dht11);
249 #endif
250 
251                 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
252                         dev_err(dht11->dev, "Only %d signal edges detected\n",
253                                 dht11->num_edges);
254                         ret = -ETIMEDOUT;
255                 }
256                 if (ret < 0)
257                         goto err;
258 
259                 offset = DHT11_EDGES_PREAMBLE +
260                                 dht11->num_edges - DHT11_EDGES_PER_READ;
261                 for (; offset >= 0; --offset) {
262                         ret = dht11_decode(dht11, offset);
263                         if (!ret)
264                                 break;
265                 }
266 
267                 if (ret)
268                         goto err;
269         }
270 
271         ret = IIO_VAL_INT;
272         if (chan->type == IIO_TEMP)
273                 *val = dht11->temperature;
274         else if (chan->type == IIO_HUMIDITYRELATIVE)
275                 *val = dht11->humidity;
276         else
277                 ret = -EINVAL;
278 err:
279         dht11->num_edges = -1;
280         mutex_unlock(&dht11->lock);
281         return ret;
282 }
283 
284 static const struct iio_info dht11_iio_info = {
285         .driver_module          = THIS_MODULE,
286         .read_raw               = dht11_read_raw,
287 };
288 
289 static const struct iio_chan_spec dht11_chan_spec[] = {
290         { .type = IIO_TEMP,
291                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
292         { .type = IIO_HUMIDITYRELATIVE,
293                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
294 };
295 
296 static const struct of_device_id dht11_dt_ids[] = {
297         { .compatible = "dht11", },
298         { }
299 };
300 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
301 
302 static int dht11_probe(struct platform_device *pdev)
303 {
304         struct device *dev = &pdev->dev;
305         struct device_node *node = dev->of_node;
306         struct dht11 *dht11;
307         struct iio_dev *iio;
308         int ret;
309 
310         iio = devm_iio_device_alloc(dev, sizeof(*dht11));
311         if (!iio) {
312                 dev_err(dev, "Failed to allocate IIO device\n");
313                 return -ENOMEM;
314         }
315 
316         dht11 = iio_priv(iio);
317         dht11->dev = dev;
318 
319         ret = of_get_gpio(node, 0);
320         if (ret < 0)
321                 return ret;
322         dht11->gpio = ret;
323         ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
324         if (ret)
325                 return ret;
326 
327         dht11->irq = gpio_to_irq(dht11->gpio);
328         if (dht11->irq < 0) {
329                 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
330                 return -EINVAL;
331         }
332 
333         dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1;
334         dht11->num_edges = -1;
335 
336         platform_set_drvdata(pdev, iio);
337 
338         init_completion(&dht11->completion);
339         mutex_init(&dht11->lock);
340         iio->name = pdev->name;
341         iio->dev.parent = &pdev->dev;
342         iio->info = &dht11_iio_info;
343         iio->modes = INDIO_DIRECT_MODE;
344         iio->channels = dht11_chan_spec;
345         iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
346 
347         return devm_iio_device_register(dev, iio);
348 }
349 
350 static struct platform_driver dht11_driver = {
351         .driver = {
352                 .name   = DRIVER_NAME,
353                 .of_match_table = dht11_dt_ids,
354         },
355         .probe  = dht11_probe,
356 };
357 
358 module_platform_driver(dht11_driver);
359 
360 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
361 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
362 MODULE_LICENSE("GPL v2");
363 

This page was automatically generated by LXR 0.3.1 (source).  •  Linux is a registered trademark of Linus Torvalds  •  Contact us