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");