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        18  /* ms */
  75 #define DHT11_MIN_TIMERES       34000  /* ns */
  76 #define DHT11_THRESHOLD         49000  /* ns */
  77 #define DHT11_AMBIG_LOW         23000  /* ns */
  78 #define DHT11_AMBIG_HIGH        30000  /* ns */
  79
  80 struct dht11 {
  81         struct device                   *dev;
  82
  83         int                             gpio;
  84         int                             irq;
  85
  86         struct completion               completion;
  87         /* The iio sysfs interface doesn't prevent concurrent reads: */
  88         struct mutex                    lock;
  89
  90         s64                             timestamp;
  91         int                             temperature;
  92         int                             humidity;
  93
  94         /* num_edges: -1 means "no transmission in progress" */
  95         int                             num_edges;
  96         struct {s64 ts; int value; }    edges[DHT11_EDGES_PER_READ];
  97 };
  98
  99 static unsigned char dht11_decode_byte(char *bits)
 100 {
 101         unsigned char ret = 0;
 102         int i;
 103
 104         for (i = 0; i < 8; ++i) {
 105                 ret <<= 1;
 106                 if (bits[i])
 107                         ++ret;
 108         }
 109
 110         return ret;
 111 }
 112
 113 static int dht11_decode(struct dht11 *dht11, int offset)
 114 {
 115         int i, t;
 116         char bits[DHT11_BITS_PER_READ];
 117         unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
 118
 119         for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
 120                 t = dht11->edges[offset + 2 * i + 2].ts -
 121                         dht11->edges[offset + 2 * i + 1].ts;
 122                 if (!dht11->edges[offset + 2 * i + 1].value)
 123                         return -EIO;  /* lost synchronisation */
 124                 bits[i] = t > DHT11_THRESHOLD;
 125         }
 126
 127         hum_int = dht11_decode_byte(bits);
 128         hum_dec = dht11_decode_byte(&bits[8]);
 129         temp_int = dht11_decode_byte(&bits[16]);
 130         temp_dec = dht11_decode_byte(&bits[24]);
 131         checksum = dht11_decode_byte(&bits[32]);
 132
 133         if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum)
 134                 return -EIO;
 135
 136         dht11->timestamp = ktime_get_boot_ns();
 137         if (hum_int < 20) {  /* DHT22 */
 138                 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
 139                                         ((temp_int & 0x80) ? -100 : 100);
 140                 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
 141         } else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
 142                 dht11->temperature = temp_int * 1000;
 143                 dht11->humidity = hum_int * 1000;
 144         } else {
 145                 dev_err(dht11->dev,
 146                         "Don't know how to decode data: %d %d %d %d\n",
 147                         hum_int, hum_dec, temp_int, temp_dec);
 148                 return -EIO;
 149         }
 150
 151         return 0;
 152 }
 153
 154 /*
 155  * IRQ handler called on GPIO edges
 156  */
 157 static irqreturn_t dht11_handle_irq(int irq, void *data)
 158 {
 159         struct iio_dev *iio = data;
 160         struct dht11 *dht11 = iio_priv(iio);
 161
 162         /* TODO: Consider making the handler safe for IRQ sharing */
 163         if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
 164                 dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns();
 165                 dht11->edges[dht11->num_edges++].value =
 166                                                 gpio_get_value(dht11->gpio);
 167
 168                 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
 169                         complete(&dht11->completion);
 170         }
 171
 172         return IRQ_HANDLED;
 173 }
 174
 175 static int dht11_read_raw(struct iio_dev *iio_dev,
 176                           const struct iio_chan_spec *chan,
 177                         int *val, int *val2, long m)
 178 {
 179         struct dht11 *dht11 = iio_priv(iio_dev);
 180         int ret, timeres, offset;
 181
 182         mutex_lock(&dht11->lock);
 183         if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) {
 184                 timeres = ktime_get_resolution_ns();
 185                 if (timeres > DHT11_MIN_TIMERES) {
 186                         dev_err(dht11->dev, "timeresolution %dns too low\n",
 187                                 timeres);
 188                         /* In theory a better clock could become available
 189                          * at some point ... and there is no error code
 190                          * that really fits better.
 191                          */
 192                         ret = -EAGAIN;
 193                         goto err;
 194                 }
 195                 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)
 196                         dev_warn(dht11->dev,
 197                                  "timeresolution: %dns - decoding ambiguous\n",
 198                                  timeres);
 199
 200                 reinit_completion(&dht11->completion);
 201
 202                 dht11->num_edges = 0;
 203                 ret = gpio_direction_output(dht11->gpio, 0);
 204                 if (ret)
 205                         goto err;
 206                 msleep(DHT11_START_TRANSMISSION);
 207                 ret = gpio_direction_input(dht11->gpio);
 208                 if (ret)
 209                         goto err;
 210
 211                 ret = request_irq(dht11->irq, dht11_handle_irq,
 212                                   IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
 213                                   iio_dev->name, iio_dev);
 214                 if (ret)
 215                         goto err;
 216
 217                 ret = wait_for_completion_killable_timeout(&dht11->completion,
 218                                                            HZ);
 219
 220                 free_irq(dht11->irq, iio_dev);
 221
 222                 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
 223                         dev_err(&iio_dev->dev,
 224                                 "Only %d signal edges detected\n",
 225                                         dht11->num_edges);
 226                         ret = -ETIMEDOUT;
 227                 }
 228                 if (ret < 0)
 229                         goto err;
 230
 231                 offset = DHT11_EDGES_PREAMBLE +
 232                                 dht11->num_edges - DHT11_EDGES_PER_READ;
 233                 for (; offset >= 0; --offset) {
 234                         ret = dht11_decode(dht11, offset);
 235                         if (!ret)
 236                                 break;
 237                 }
 238
 239                 if (ret)
 240                         goto err;
 241         }
 242
 243         ret = IIO_VAL_INT;
 244         if (chan->type == IIO_TEMP)
 245                 *val = dht11->temperature;
 246         else if (chan->type == IIO_HUMIDITYRELATIVE)
 247                 *val = dht11->humidity;
 248         else
 249                 ret = -EINVAL;
 250 err:
 251         dht11->num_edges = -1;
 252         mutex_unlock(&dht11->lock);
 253         return ret;
 254 }
 255
 256 static const struct iio_info dht11_iio_info = {
 257         .driver_module          = THIS_MODULE,
 258         .read_raw               = dht11_read_raw,
 259 };
 260
 261 static const struct iio_chan_spec dht11_chan_spec[] = {
 262         { .type = IIO_TEMP,
 263                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
 264         { .type = IIO_HUMIDITYRELATIVE,
 265                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
 266 };
 267
 268 static const struct of_device_id dht11_dt_ids[] = {
 269         { .compatible = "dht11", },
 270         { }
 271 };
 272 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
 273
 274 static int dht11_probe(struct platform_device *pdev)
 275 {
 276         struct device *dev = &pdev->dev;
 277         struct device_node *node = dev->of_node;
 278         struct dht11 *dht11;
 279         struct iio_dev *iio;
 280         int ret;
 281
 282         iio = devm_iio_device_alloc(dev, sizeof(*dht11));
 283         if (!iio) {
 284                 dev_err(dev, "Failed to allocate IIO device\n");
 285                 return -ENOMEM;
 286         }
 287
 288         dht11 = iio_priv(iio);
 289         dht11->dev = dev;
 290
 291         ret = of_get_gpio(node, 0);
 292         if (ret < 0)
 293                 return ret;
 294         dht11->gpio = ret;
 295         ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
 296         if (ret)
 297                 return ret;
 298
 299         dht11->irq = gpio_to_irq(dht11->gpio);
 300         if (dht11->irq < 0) {
 301                 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
 302                 return -EINVAL;
 303         }
 304
 305         dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1;
 306         dht11->num_edges = -1;
 307
 308         platform_set_drvdata(pdev, iio);
 309
 310         init_completion(&dht11->completion);
 311         mutex_init(&dht11->lock);
 312         iio->name = pdev->name;
 313         iio->dev.parent = &pdev->dev;
 314         iio->info = &dht11_iio_info;
 315         iio->modes = INDIO_DIRECT_MODE;
 316         iio->channels = dht11_chan_spec;
 317         iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
 318
 319         return devm_iio_device_register(dev, iio);
 320 }
 321
 322 static struct platform_driver dht11_driver = {
 323         .driver = {
 324                 .name   = DRIVER_NAME,
 325                 .of_match_table = dht11_dt_ids,
 326         },
 327         .probe  = dht11_probe,
 328 };
 329
 330 module_platform_driver(dht11_driver);
 331
 332 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
 333 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
 334 MODULE_LICENSE("GPL v2");