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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_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 
 81 struct 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  */
105 static 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 
118 static 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 
132 static 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 < 20) {  /* DHT22 */
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  */
182 static 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 
200 static 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;
280 err:
281         dht11->num_edges = -1;
282         mutex_unlock(&dht11->lock);
283         return ret;
284 }
285 
286 static const struct iio_info dht11_iio_info = {
287         .driver_module          = THIS_MODULE,
288         .read_raw               = dht11_read_raw,
289 };
290 
291 static const struct iio_chan_spec dht11_chan_spec[] = {
292         { .type = IIO_TEMP,
293                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
294         { .type = IIO_HUMIDITYRELATIVE,
295                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
296 };
297 
298 static const struct of_device_id dht11_dt_ids[] = {
299         { .compatible = "dht11", },
300         { }
301 };
302 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
303 
304 static int dht11_probe(struct platform_device *pdev)
305 {
306         struct device *dev = &pdev->dev;
307         struct device_node *node = dev->of_node;
308         struct dht11 *dht11;
309         struct iio_dev *iio;
310         int ret;
311 
312         iio = devm_iio_device_alloc(dev, sizeof(*dht11));
313         if (!iio) {
314                 dev_err(dev, "Failed to allocate IIO device\n");
315                 return -ENOMEM;
316         }
317 
318         dht11 = iio_priv(iio);
319         dht11->dev = dev;
320 
321         ret = of_get_gpio(node, 0);
322         if (ret < 0)
323                 return ret;
324         dht11->gpio = ret;
325         ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
326         if (ret)
327                 return ret;
328 
329         dht11->irq = gpio_to_irq(dht11->gpio);
330         if (dht11->irq < 0) {
331                 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
332                 return -EINVAL;
333         }
334 
335         dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1;
336         dht11->num_edges = -1;
337 
338         platform_set_drvdata(pdev, iio);
339 
340         init_completion(&dht11->completion);
341         mutex_init(&dht11->lock);
342         iio->name = pdev->name;
343         iio->dev.parent = &pdev->dev;
344         iio->info = &dht11_iio_info;
345         iio->modes = INDIO_DIRECT_MODE;
346         iio->channels = dht11_chan_spec;
347         iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
348 
349         return devm_iio_device_register(dev, iio);
350 }
351 
352 static struct platform_driver dht11_driver = {
353         .driver = {
354                 .name   = DRIVER_NAME,
355                 .of_match_table = dht11_dt_ids,
356         },
357         .probe  = dht11_probe,
358 };
359 
360 module_platform_driver(dht11_driver);
361 
362 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
363 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
364 MODULE_LICENSE("GPL v2");
365 

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