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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 /* Data transmission timing (nano seconds) */
 54 #define DHT11_START_TRANSMISSION        18  /* ms */
 55 #define DHT11_SENSOR_RESPONSE   80000
 56 #define DHT11_START_BIT         50000
 57 #define DHT11_DATA_BIT_LOW      27000
 58 #define DHT11_DATA_BIT_HIGH     70000
 59 
 60 struct dht11 {
 61         struct device                   *dev;
 62 
 63         int                             gpio;
 64         int                             irq;
 65 
 66         struct completion               completion;
 67         /* The iio sysfs interface doesn't prevent concurrent reads: */
 68         struct mutex                    lock;
 69 
 70         s64                             timestamp;
 71         int                             temperature;
 72         int                             humidity;
 73 
 74         /* num_edges: -1 means "no transmission in progress" */
 75         int                             num_edges;
 76         struct {s64 ts; int value; }    edges[DHT11_EDGES_PER_READ];
 77 };
 78 
 79 static unsigned char dht11_decode_byte(int *timing, int threshold)
 80 {
 81         unsigned char ret = 0;
 82         int i;
 83 
 84         for (i = 0; i < 8; ++i) {
 85                 ret <<= 1;
 86                 if (timing[i] >= threshold)
 87                         ++ret;
 88         }
 89 
 90         return ret;
 91 }
 92 
 93 static int dht11_decode(struct dht11 *dht11, int offset, int timeres)
 94 {
 95         int i, t, timing[DHT11_BITS_PER_READ], threshold;
 96         unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
 97 
 98         threshold = DHT11_DATA_BIT_HIGH / timeres;
 99         if (DHT11_DATA_BIT_LOW / timeres + 1 >= threshold)
100                 pr_err("dht11: WARNING: decoding ambiguous\n");
101 
102         /* scale down with timeres and check validity */
103         for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
104                 t = dht11->edges[offset + 2 * i + 2].ts -
105                         dht11->edges[offset + 2 * i + 1].ts;
106                 if (!dht11->edges[offset + 2 * i + 1].value)
107                         return -EIO;  /* lost synchronisation */
108                 timing[i] = t / timeres;
109         }
110 
111         hum_int = dht11_decode_byte(timing, threshold);
112         hum_dec = dht11_decode_byte(&timing[8], threshold);
113         temp_int = dht11_decode_byte(&timing[16], threshold);
114         temp_dec = dht11_decode_byte(&timing[24], threshold);
115         checksum = dht11_decode_byte(&timing[32], threshold);
116 
117         if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum)
118                 return -EIO;
119 
120         dht11->timestamp = ktime_get_real_ns();
121         if (hum_int < 20) {  /* DHT22 */
122                 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
123                                         ((temp_int & 0x80) ? -100 : 100);
124                 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
125         } else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
126                 dht11->temperature = temp_int * 1000;
127                 dht11->humidity = hum_int * 1000;
128         } else {
129                 dev_err(dht11->dev,
130                         "Don't know how to decode data: %d %d %d %d\n",
131                         hum_int, hum_dec, temp_int, temp_dec);
132                 return -EIO;
133         }
134 
135         return 0;
136 }
137 
138 /*
139  * IRQ handler called on GPIO edges
140  */
141 static irqreturn_t dht11_handle_irq(int irq, void *data)
142 {
143         struct iio_dev *iio = data;
144         struct dht11 *dht11 = iio_priv(iio);
145 
146         /* TODO: Consider making the handler safe for IRQ sharing */
147         if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
148                 dht11->edges[dht11->num_edges].ts = ktime_get_real_ns();
149                 dht11->edges[dht11->num_edges++].value =
150                                                 gpio_get_value(dht11->gpio);
151 
152                 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
153                         complete(&dht11->completion);
154         }
155 
156         return IRQ_HANDLED;
157 }
158 
159 static int dht11_read_raw(struct iio_dev *iio_dev,
160                           const struct iio_chan_spec *chan,
161                         int *val, int *val2, long m)
162 {
163         struct dht11 *dht11 = iio_priv(iio_dev);
164         int ret, timeres;
165 
166         mutex_lock(&dht11->lock);
167         if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_real_ns()) {
168                 timeres = ktime_get_resolution_ns();
169                 if (DHT11_DATA_BIT_HIGH < 2 * timeres) {
170                         dev_err(dht11->dev, "timeresolution %dns too low\n",
171                                 timeres);
172                         /* In theory a better clock could become available
173                          * at some point ... and there is no error code
174                          * that really fits better.
175                          */
176                         ret = -EAGAIN;
177                         goto err;
178                 }
179 
180                 reinit_completion(&dht11->completion);
181 
182                 dht11->num_edges = 0;
183                 ret = gpio_direction_output(dht11->gpio, 0);
184                 if (ret)
185                         goto err;
186                 msleep(DHT11_START_TRANSMISSION);
187                 ret = gpio_direction_input(dht11->gpio);
188                 if (ret)
189                         goto err;
190 
191                 ret = request_irq(dht11->irq, dht11_handle_irq,
192                                   IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
193                                   iio_dev->name, iio_dev);
194                 if (ret)
195                         goto err;
196 
197                 ret = wait_for_completion_killable_timeout(&dht11->completion,
198                                                            HZ);
199 
200                 free_irq(dht11->irq, iio_dev);
201 
202                 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
203                         dev_err(&iio_dev->dev,
204                                 "Only %d signal edges detected\n",
205                                         dht11->num_edges);
206                         ret = -ETIMEDOUT;
207                 }
208                 if (ret < 0)
209                         goto err;
210 
211                 ret = dht11_decode(dht11,
212                                    dht11->num_edges == DHT11_EDGES_PER_READ ?
213                                         DHT11_EDGES_PREAMBLE :
214                                         DHT11_EDGES_PREAMBLE - 2,
215                                 timeres);
216                 if (ret)
217                         goto err;
218         }
219 
220         ret = IIO_VAL_INT;
221         if (chan->type == IIO_TEMP)
222                 *val = dht11->temperature;
223         else if (chan->type == IIO_HUMIDITYRELATIVE)
224                 *val = dht11->humidity;
225         else
226                 ret = -EINVAL;
227 err:
228         dht11->num_edges = -1;
229         mutex_unlock(&dht11->lock);
230         return ret;
231 }
232 
233 static const struct iio_info dht11_iio_info = {
234         .driver_module          = THIS_MODULE,
235         .read_raw               = dht11_read_raw,
236 };
237 
238 static const struct iio_chan_spec dht11_chan_spec[] = {
239         { .type = IIO_TEMP,
240                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
241         { .type = IIO_HUMIDITYRELATIVE,
242                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
243 };
244 
245 static const struct of_device_id dht11_dt_ids[] = {
246         { .compatible = "dht11", },
247         { }
248 };
249 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
250 
251 static int dht11_probe(struct platform_device *pdev)
252 {
253         struct device *dev = &pdev->dev;
254         struct device_node *node = dev->of_node;
255         struct dht11 *dht11;
256         struct iio_dev *iio;
257         int ret;
258 
259         iio = devm_iio_device_alloc(dev, sizeof(*dht11));
260         if (!iio) {
261                 dev_err(dev, "Failed to allocate IIO device\n");
262                 return -ENOMEM;
263         }
264 
265         dht11 = iio_priv(iio);
266         dht11->dev = dev;
267 
268         ret = of_get_gpio(node, 0);
269         if (ret < 0)
270                 return ret;
271         dht11->gpio = ret;
272         ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
273         if (ret)
274                 return ret;
275 
276         dht11->irq = gpio_to_irq(dht11->gpio);
277         if (dht11->irq < 0) {
278                 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
279                 return -EINVAL;
280         }
281 
282         dht11->timestamp = ktime_get_real_ns() - DHT11_DATA_VALID_TIME - 1;
283         dht11->num_edges = -1;
284 
285         platform_set_drvdata(pdev, iio);
286 
287         init_completion(&dht11->completion);
288         mutex_init(&dht11->lock);
289         iio->name = pdev->name;
290         iio->dev.parent = &pdev->dev;
291         iio->info = &dht11_iio_info;
292         iio->modes = INDIO_DIRECT_MODE;
293         iio->channels = dht11_chan_spec;
294         iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
295 
296         return devm_iio_device_register(dev, iio);
297 }
298 
299 static struct platform_driver dht11_driver = {
300         .driver = {
301                 .name   = DRIVER_NAME,
302                 .of_match_table = dht11_dt_ids,
303         },
304         .probe  = dht11_probe,
305 };
306 
307 module_platform_driver(dht11_driver);
308 
309 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
310 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
311 MODULE_LICENSE("GPL v2");
312 

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