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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/delay.h>
 33 #include <linux/gpio.h>
 34 #include <linux/of_gpio.h>
 35 
 36 #include <linux/iio/iio.h>
 37 
 38 #define DRIVER_NAME     "dht11"
 39 
 40 #define DHT11_DATA_VALID_TIME   2000000000  /* 2s in ns */
 41 
 42 #define DHT11_EDGES_PREAMBLE 4
 43 #define DHT11_BITS_PER_READ 40
 44 #define DHT11_EDGES_PER_READ (2*DHT11_BITS_PER_READ + DHT11_EDGES_PREAMBLE + 1)
 45 
 46 /* Data transmission timing (nano seconds) */
 47 #define DHT11_START_TRANSMISSION        18  /* ms */
 48 #define DHT11_SENSOR_RESPONSE   80000
 49 #define DHT11_START_BIT         50000
 50 #define DHT11_DATA_BIT_LOW      27000
 51 #define DHT11_DATA_BIT_HIGH     70000
 52 
 53 struct dht11 {
 54         struct device                   *dev;
 55 
 56         int                             gpio;
 57         int                             irq;
 58 
 59         struct completion               completion;
 60 
 61         s64                             timestamp;
 62         int                             temperature;
 63         int                             humidity;
 64 
 65         /* num_edges: -1 means "no transmission in progress" */
 66         int                             num_edges;
 67         struct {s64 ts; int value; }    edges[DHT11_EDGES_PER_READ];
 68 };
 69 
 70 static unsigned char dht11_decode_byte(int *timing, int threshold)
 71 {
 72         unsigned char ret = 0;
 73         int i;
 74 
 75         for (i = 0; i < 8; ++i) {
 76                 ret <<= 1;
 77                 if (timing[i] >= threshold)
 78                         ++ret;
 79         }
 80 
 81         return ret;
 82 }
 83 
 84 static int dht11_decode(struct dht11 *dht11, int offset)
 85 {
 86         int i, t, timing[DHT11_BITS_PER_READ], threshold,
 87                 timeres = DHT11_SENSOR_RESPONSE;
 88         unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
 89 
 90         /* Calculate timestamp resolution */
 91         for (i = 0; i < dht11->num_edges; ++i) {
 92                 t = dht11->edges[i].ts - dht11->edges[i-1].ts;
 93                 if (t > 0 && t < timeres)
 94                         timeres = t;
 95         }
 96         if (2*timeres > DHT11_DATA_BIT_HIGH) {
 97                 pr_err("dht11: timeresolution %d too bad for decoding\n",
 98                         timeres);
 99                 return -EIO;
100         }
101         threshold = DHT11_DATA_BIT_HIGH / timeres;
102         if (DHT11_DATA_BIT_LOW/timeres + 1 >= threshold)
103                 pr_err("dht11: WARNING: decoding ambiguous\n");
104 
105         /* scale down with timeres and check validity */
106         for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
107                 t = dht11->edges[offset + 2*i + 2].ts -
108                         dht11->edges[offset + 2*i + 1].ts;
109                 if (!dht11->edges[offset + 2*i + 1].value)
110                         return -EIO;  /* lost synchronisation */
111                 timing[i] = t / timeres;
112         }
113 
114         hum_int = dht11_decode_byte(timing, threshold);
115         hum_dec = dht11_decode_byte(&timing[8], threshold);
116         temp_int = dht11_decode_byte(&timing[16], threshold);
117         temp_dec = dht11_decode_byte(&timing[24], threshold);
118         checksum = dht11_decode_byte(&timing[32], threshold);
119 
120         if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum)
121                 return -EIO;
122 
123         dht11->timestamp = iio_get_time_ns();
124         if (hum_int < 20) {  /* DHT22 */
125                 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
126                                         ((temp_int & 0x80) ? -100 : 100);
127                 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
128         } else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
129                 dht11->temperature = temp_int * 1000;
130                 dht11->humidity = hum_int * 1000;
131         } else {
132                 dev_err(dht11->dev,
133                         "Don't know how to decode data: %d %d %d %d\n",
134                         hum_int, hum_dec, temp_int, temp_dec);
135                 return -EIO;
136         }
137 
138         return 0;
139 }
140 
141 static int dht11_read_raw(struct iio_dev *iio_dev,
142                         const struct iio_chan_spec *chan,
143                         int *val, int *val2, long m)
144 {
145         struct dht11 *dht11 = iio_priv(iio_dev);
146         int ret;
147 
148         if (dht11->timestamp + DHT11_DATA_VALID_TIME < iio_get_time_ns()) {
149                 reinit_completion(&dht11->completion);
150 
151                 dht11->num_edges = 0;
152                 ret = gpio_direction_output(dht11->gpio, 0);
153                 if (ret)
154                         goto err;
155                 msleep(DHT11_START_TRANSMISSION);
156                 ret = gpio_direction_input(dht11->gpio);
157                 if (ret)
158                         goto err;
159 
160                 ret = wait_for_completion_killable_timeout(&dht11->completion,
161                                                                  HZ);
162                 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
163                         dev_err(&iio_dev->dev,
164                                         "Only %d signal edges detected\n",
165                                         dht11->num_edges);
166                         ret = -ETIMEDOUT;
167                 }
168                 if (ret < 0)
169                         goto err;
170 
171                 ret = dht11_decode(dht11,
172                                 dht11->num_edges == DHT11_EDGES_PER_READ ?
173                                         DHT11_EDGES_PREAMBLE :
174                                         DHT11_EDGES_PREAMBLE - 2);
175                 if (ret)
176                         goto err;
177         }
178 
179         ret = IIO_VAL_INT;
180         if (chan->type == IIO_TEMP)
181                 *val = dht11->temperature;
182         else if (chan->type == IIO_HUMIDITYRELATIVE)
183                 *val = dht11->humidity;
184         else
185                 ret = -EINVAL;
186 err:
187         dht11->num_edges = -1;
188         return ret;
189 }
190 
191 static const struct iio_info dht11_iio_info = {
192         .driver_module          = THIS_MODULE,
193         .read_raw               = dht11_read_raw,
194 };
195 
196 /*
197  * IRQ handler called on GPIO edges
198 */
199 static irqreturn_t dht11_handle_irq(int irq, void *data)
200 {
201         struct iio_dev *iio = data;
202         struct dht11 *dht11 = iio_priv(iio);
203 
204         /* TODO: Consider making the handler safe for IRQ sharing */
205         if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
206                 dht11->edges[dht11->num_edges].ts = iio_get_time_ns();
207                 dht11->edges[dht11->num_edges++].value =
208                                                 gpio_get_value(dht11->gpio);
209 
210                 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
211                         complete(&dht11->completion);
212         }
213 
214         return IRQ_HANDLED;
215 }
216 
217 static const struct iio_chan_spec dht11_chan_spec[] = {
218         { .type = IIO_TEMP,
219                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
220         { .type = IIO_HUMIDITYRELATIVE,
221                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
222 };
223 
224 static const struct of_device_id dht11_dt_ids[] = {
225         { .compatible = "dht11", },
226         { }
227 };
228 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
229 
230 static int dht11_probe(struct platform_device *pdev)
231 {
232         struct device *dev = &pdev->dev;
233         struct device_node *node = dev->of_node;
234         struct dht11 *dht11;
235         struct iio_dev *iio;
236         int ret;
237 
238         iio = devm_iio_device_alloc(dev, sizeof(*dht11));
239         if (!iio) {
240                 dev_err(dev, "Failed to allocate IIO device\n");
241                 return -ENOMEM;
242         }
243 
244         dht11 = iio_priv(iio);
245         dht11->dev = dev;
246 
247         dht11->gpio = ret = of_get_gpio(node, 0);
248         if (ret < 0)
249                 return ret;
250         ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
251         if (ret)
252                 return ret;
253 
254         dht11->irq = gpio_to_irq(dht11->gpio);
255         if (dht11->irq < 0) {
256                 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
257                 return -EINVAL;
258         }
259         ret = devm_request_irq(dev, dht11->irq, dht11_handle_irq,
260                                 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
261                                 pdev->name, iio);
262         if (ret)
263                 return ret;
264 
265         dht11->timestamp = iio_get_time_ns() - DHT11_DATA_VALID_TIME - 1;
266         dht11->num_edges = -1;
267 
268         platform_set_drvdata(pdev, iio);
269 
270         init_completion(&dht11->completion);
271         iio->name = pdev->name;
272         iio->dev.parent = &pdev->dev;
273         iio->info = &dht11_iio_info;
274         iio->modes = INDIO_DIRECT_MODE;
275         iio->channels = dht11_chan_spec;
276         iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
277 
278         return devm_iio_device_register(dev, iio);
279 }
280 
281 static struct platform_driver dht11_driver = {
282         .driver = {
283                 .name   = DRIVER_NAME,
284                 .owner  = THIS_MODULE,
285                 .of_match_table = dht11_dt_ids,
286         },
287         .probe  = dht11_probe,
288 };
289 
290 module_platform_driver(dht11_driver);
291 
292 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
293 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
294 MODULE_LICENSE("GPL v2");
295 

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