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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 
 37 #include <linux/iio/iio.h>
 38 
 39 #define DRIVER_NAME     "dht11"
 40 
 41 #define DHT11_DATA_VALID_TIME   2000000000  /* 2s in ns */
 42 
 43 #define DHT11_EDGES_PREAMBLE 2
 44 #define DHT11_BITS_PER_READ 40
 45 /*
 46  * Note that when reading the sensor actually 84 edges are detected, but
 47  * since the last edge is not significant, we only store 83:
 48  */
 49 #define DHT11_EDGES_PER_READ (2*DHT11_BITS_PER_READ + DHT11_EDGES_PREAMBLE + 1)
 50 
 51 /* Data transmission timing (nano seconds) */
 52 #define DHT11_START_TRANSMISSION        18  /* ms */
 53 #define DHT11_SENSOR_RESPONSE   80000
 54 #define DHT11_START_BIT         50000
 55 #define DHT11_DATA_BIT_LOW      27000
 56 #define DHT11_DATA_BIT_HIGH     70000
 57 
 58 struct dht11 {
 59         struct device                   *dev;
 60 
 61         int                             gpio;
 62         int                             irq;
 63 
 64         struct completion               completion;
 65         struct mutex                    lock;
 66 
 67         s64                             timestamp;
 68         int                             temperature;
 69         int                             humidity;
 70 
 71         /* num_edges: -1 means "no transmission in progress" */
 72         int                             num_edges;
 73         struct {s64 ts; int value; }    edges[DHT11_EDGES_PER_READ];
 74 };
 75 
 76 static unsigned char dht11_decode_byte(int *timing, int threshold)
 77 {
 78         unsigned char ret = 0;
 79         int i;
 80 
 81         for (i = 0; i < 8; ++i) {
 82                 ret <<= 1;
 83                 if (timing[i] >= threshold)
 84                         ++ret;
 85         }
 86 
 87         return ret;
 88 }
 89 
 90 static int dht11_decode(struct dht11 *dht11, int offset)
 91 {
 92         int i, t, timing[DHT11_BITS_PER_READ], threshold,
 93                 timeres = DHT11_SENSOR_RESPONSE;
 94         unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
 95 
 96         /* Calculate timestamp resolution */
 97         for (i = 1; i < dht11->num_edges; ++i) {
 98                 t = dht11->edges[i].ts - dht11->edges[i-1].ts;
 99                 if (t > 0 && t < timeres)
100                         timeres = t;
101         }
102         if (2*timeres > DHT11_DATA_BIT_HIGH) {
103                 pr_err("dht11: timeresolution %d too bad for decoding\n",
104                         timeres);
105                 return -EIO;
106         }
107         threshold = DHT11_DATA_BIT_HIGH / timeres;
108         if (DHT11_DATA_BIT_LOW/timeres + 1 >= threshold)
109                 pr_err("dht11: WARNING: decoding ambiguous\n");
110 
111         /* scale down with timeres and check validity */
112         for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
113                 t = dht11->edges[offset + 2*i + 2].ts -
114                         dht11->edges[offset + 2*i + 1].ts;
115                 if (!dht11->edges[offset + 2*i + 1].value)
116                         return -EIO;  /* lost synchronisation */
117                 timing[i] = t / timeres;
118         }
119 
120         hum_int = dht11_decode_byte(timing, threshold);
121         hum_dec = dht11_decode_byte(&timing[8], threshold);
122         temp_int = dht11_decode_byte(&timing[16], threshold);
123         temp_dec = dht11_decode_byte(&timing[24], threshold);
124         checksum = dht11_decode_byte(&timing[32], threshold);
125 
126         if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum)
127                 return -EIO;
128 
129         dht11->timestamp = iio_get_time_ns();
130         if (hum_int < 20) {  /* DHT22 */
131                 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
132                                         ((temp_int & 0x80) ? -100 : 100);
133                 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
134         } else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
135                 dht11->temperature = temp_int * 1000;
136                 dht11->humidity = hum_int * 1000;
137         } else {
138                 dev_err(dht11->dev,
139                         "Don't know how to decode data: %d %d %d %d\n",
140                         hum_int, hum_dec, temp_int, temp_dec);
141                 return -EIO;
142         }
143 
144         return 0;
145 }
146 
147 /*
148  * IRQ handler called on GPIO edges
149  */
150 static irqreturn_t dht11_handle_irq(int irq, void *data)
151 {
152         struct iio_dev *iio = data;
153         struct dht11 *dht11 = iio_priv(iio);
154 
155         /* TODO: Consider making the handler safe for IRQ sharing */
156         if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
157                 dht11->edges[dht11->num_edges].ts = iio_get_time_ns();
158                 dht11->edges[dht11->num_edges++].value =
159                                                 gpio_get_value(dht11->gpio);
160 
161                 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
162                         complete(&dht11->completion);
163         }
164 
165         return IRQ_HANDLED;
166 }
167 
168 static int dht11_read_raw(struct iio_dev *iio_dev,
169                         const struct iio_chan_spec *chan,
170                         int *val, int *val2, long m)
171 {
172         struct dht11 *dht11 = iio_priv(iio_dev);
173         int ret;
174 
175         mutex_lock(&dht11->lock);
176         if (dht11->timestamp + DHT11_DATA_VALID_TIME < iio_get_time_ns()) {
177                 reinit_completion(&dht11->completion);
178 
179                 dht11->num_edges = 0;
180                 ret = gpio_direction_output(dht11->gpio, 0);
181                 if (ret)
182                         goto err;
183                 msleep(DHT11_START_TRANSMISSION);
184                 ret = gpio_direction_input(dht11->gpio);
185                 if (ret)
186                         goto err;
187 
188                 ret = request_irq(dht11->irq, dht11_handle_irq,
189                                   IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
190                                   iio_dev->name, iio_dev);
191                 if (ret)
192                         goto err;
193 
194                 ret = wait_for_completion_killable_timeout(&dht11->completion,
195                                                                  HZ);
196 
197                 free_irq(dht11->irq, iio_dev);
198 
199                 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
200                         dev_err(&iio_dev->dev,
201                                         "Only %d signal edges detected\n",
202                                         dht11->num_edges);
203                         ret = -ETIMEDOUT;
204                 }
205                 if (ret < 0)
206                         goto err;
207 
208                 ret = dht11_decode(dht11,
209                                 dht11->num_edges == DHT11_EDGES_PER_READ ?
210                                         DHT11_EDGES_PREAMBLE :
211                                         DHT11_EDGES_PREAMBLE - 2);
212                 if (ret)
213                         goto err;
214         }
215 
216         ret = IIO_VAL_INT;
217         if (chan->type == IIO_TEMP)
218                 *val = dht11->temperature;
219         else if (chan->type == IIO_HUMIDITYRELATIVE)
220                 *val = dht11->humidity;
221         else
222                 ret = -EINVAL;
223 err:
224         dht11->num_edges = -1;
225         mutex_unlock(&dht11->lock);
226         return ret;
227 }
228 
229 static const struct iio_info dht11_iio_info = {
230         .driver_module          = THIS_MODULE,
231         .read_raw               = dht11_read_raw,
232 };
233 
234 static const struct iio_chan_spec dht11_chan_spec[] = {
235         { .type = IIO_TEMP,
236                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
237         { .type = IIO_HUMIDITYRELATIVE,
238                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
239 };
240 
241 static const struct of_device_id dht11_dt_ids[] = {
242         { .compatible = "dht11", },
243         { }
244 };
245 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
246 
247 static int dht11_probe(struct platform_device *pdev)
248 {
249         struct device *dev = &pdev->dev;
250         struct device_node *node = dev->of_node;
251         struct dht11 *dht11;
252         struct iio_dev *iio;
253         int ret;
254 
255         iio = devm_iio_device_alloc(dev, sizeof(*dht11));
256         if (!iio) {
257                 dev_err(dev, "Failed to allocate IIO device\n");
258                 return -ENOMEM;
259         }
260 
261         dht11 = iio_priv(iio);
262         dht11->dev = dev;
263 
264         dht11->gpio = ret = of_get_gpio(node, 0);
265         if (ret < 0)
266                 return ret;
267         ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
268         if (ret)
269                 return ret;
270 
271         dht11->irq = gpio_to_irq(dht11->gpio);
272         if (dht11->irq < 0) {
273                 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
274                 return -EINVAL;
275         }
276 
277         dht11->timestamp = iio_get_time_ns() - DHT11_DATA_VALID_TIME - 1;
278         dht11->num_edges = -1;
279 
280         platform_set_drvdata(pdev, iio);
281 
282         init_completion(&dht11->completion);
283         mutex_init(&dht11->lock);
284         iio->name = pdev->name;
285         iio->dev.parent = &pdev->dev;
286         iio->info = &dht11_iio_info;
287         iio->modes = INDIO_DIRECT_MODE;
288         iio->channels = dht11_chan_spec;
289         iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
290 
291         return devm_iio_device_register(dev, iio);
292 }
293 
294 static struct platform_driver dht11_driver = {
295         .driver = {
296                 .name   = DRIVER_NAME,
297                 .of_match_table = dht11_dt_ids,
298         },
299         .probe  = dht11_probe,
300 };
301 
302 module_platform_driver(dht11_driver);
303 
304 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
305 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
306 MODULE_LICENSE("GPL v2");
307 

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