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_MIN    18000  /* us */
  75 #define DHT11_START_TRANSMISSION_MAX    20000  /* us */
  76 #define DHT11_MIN_TIMERES       34000  /* ns */
  77 #define DHT11_THRESHOLD         49000  /* ns */
  78 #define DHT11_AMBIG_LOW         23000  /* ns */
  79 #define DHT11_AMBIG_HIGH        30000  /* ns */
  80
  81 struct dht11 {
  82         struct device                   *dev;
  83
  84         int                             gpio;
  85         int                             irq;
  86
  87         struct completion               completion;
  88         /* The iio sysfs interface doesn't prevent concurrent reads: */
  89         struct mutex                    lock;
  90
  91         s64                             timestamp;
  92         int                             temperature;
  93         int                             humidity;
  94
  95         /* num_edges: -1 means "no transmission in progress" */
  96         int                             num_edges;
  97         struct {s64 ts; int value; }    edges[DHT11_EDGES_PER_READ];
  98 };
  99
 100 #ifdef CONFIG_DYNAMIC_DEBUG
 101 /*
 102  * dht11_edges_print: show the data as actually received by the
 103  *                    driver.
 104  */
 105 static void dht11_edges_print(struct dht11 *dht11)
 106 {
 107         int i;
 108
 109         dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);
 110         for (i = 1; i < dht11->num_edges; ++i) {
 111                 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
 112                         dht11->edges[i].ts - dht11->edges[i - 1].ts,
 113                         dht11->edges[i - 1].value ? "high" : "low");
 114         }
 115 }
 116 #endif /* CONFIG_DYNAMIC_DEBUG */
 117
 118 static unsigned char dht11_decode_byte(char *bits)
 119 {
 120         unsigned char ret = 0;
 121         int i;
 122
 123         for (i = 0; i < 8; ++i) {
 124                 ret <<= 1;
 125                 if (bits[i])
 126                         ++ret;
 127         }
 128
 129         return ret;
 130 }
 131
 132 static int dht11_decode(struct dht11 *dht11, int offset)
 133 {
 134         int i, t;
 135         char bits[DHT11_BITS_PER_READ];
 136         unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
 137
 138         for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
 139                 t = dht11->edges[offset + 2 * i + 2].ts -
 140                         dht11->edges[offset + 2 * i + 1].ts;
 141                 if (!dht11->edges[offset + 2 * i + 1].value) {
 142                         dev_dbg(dht11->dev,
 143                                 "lost synchronisation at edge %d\n",
 144                                 offset + 2 * i + 1);
 145                         return -EIO;
 146                 }
 147                 bits[i] = t > DHT11_THRESHOLD;
 148         }
 149
 150         hum_int = dht11_decode_byte(bits);
 151         hum_dec = dht11_decode_byte(&bits[8]);
 152         temp_int = dht11_decode_byte(&bits[16]);
 153         temp_dec = dht11_decode_byte(&bits[24]);
 154         checksum = dht11_decode_byte(&bits[32]);
 155
 156         if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {
 157                 dev_dbg(dht11->dev, "invalid checksum\n");
 158                 return -EIO;
 159         }
 160
 161         dht11->timestamp = ktime_get_boot_ns();
 162         if (hum_int < 20) {  /* DHT22 */
 163                 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
 164                                         ((temp_int & 0x80) ? -100 : 100);
 165                 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
 166         } else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
 167                 dht11->temperature = temp_int * 1000;
 168                 dht11->humidity = hum_int * 1000;
 169         } else {
 170                 dev_err(dht11->dev,
 171                         "Don't know how to decode data: %d %d %d %d\n",
 172                         hum_int, hum_dec, temp_int, temp_dec);
 173                 return -EIO;
 174         }
 175
 176         return 0;
 177 }
 178
 179 /*
 180  * IRQ handler called on GPIO edges
 181  */
 182 static irqreturn_t dht11_handle_irq(int irq, void *data)
 183 {
 184         struct iio_dev *iio = data;
 185         struct dht11 *dht11 = iio_priv(iio);
 186
 187         /* TODO: Consider making the handler safe for IRQ sharing */
 188         if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
 189                 dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns();
 190                 dht11->edges[dht11->num_edges++].value =
 191                                                 gpio_get_value(dht11->gpio);
 192
 193                 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
 194                         complete(&dht11->completion);
 195         }
 196
 197         return IRQ_HANDLED;
 198 }
 199
 200 static int dht11_read_raw(struct iio_dev *iio_dev,
 201                           const struct iio_chan_spec *chan,
 202                         int *val, int *val2, long m)
 203 {
 204         struct dht11 *dht11 = iio_priv(iio_dev);
 205         int ret, timeres, offset;
 206
 207         mutex_lock(&dht11->lock);
 208         if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) {
 209                 timeres = ktime_get_resolution_ns();
 210                 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);
 211                 if (timeres > DHT11_MIN_TIMERES) {
 212                         dev_err(dht11->dev, "timeresolution %dns too low\n",
 213                                 timeres);
 214                         /* In theory a better clock could become available
 215                          * at some point ... and there is no error code
 216                          * that really fits better.
 217                          */
 218                         ret = -EAGAIN;
 219                         goto err;
 220                 }
 221                 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)
 222                         dev_warn(dht11->dev,
 223                                  "timeresolution: %dns - decoding ambiguous\n",
 224                                  timeres);
 225
 226                 reinit_completion(&dht11->completion);
 227
 228                 dht11->num_edges = 0;
 229                 ret = gpio_direction_output(dht11->gpio, 0);
 230                 if (ret)
 231                         goto err;
 232                 usleep_range(DHT11_START_TRANSMISSION_MIN,
 233                              DHT11_START_TRANSMISSION_MAX);
 234                 ret = gpio_direction_input(dht11->gpio);
 235                 if (ret)
 236                         goto err;
 237
 238                 ret = request_irq(dht11->irq, dht11_handle_irq,
 239                                   IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
 240                                   iio_dev->name, iio_dev);
 241                 if (ret)
 242                         goto err;
 243
 244                 ret = wait_for_completion_killable_timeout(&dht11->completion,
 245                                                            HZ);
 246
 247                 free_irq(dht11->irq, iio_dev);
 248
 249 #ifdef CONFIG_DYNAMIC_DEBUG
 250                 dht11_edges_print(dht11);
 251 #endif
 252
 253                 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
 254                         dev_err(dht11->dev, "Only %d signal edges detected\n",
 255                                 dht11->num_edges);
 256                         ret = -ETIMEDOUT;
 257                 }
 258                 if (ret < 0)
 259                         goto err;
 260
 261                 offset = DHT11_EDGES_PREAMBLE +
 262                                 dht11->num_edges - DHT11_EDGES_PER_READ;
 263                 for (; offset >= 0; --offset) {
 264                         ret = dht11_decode(dht11, offset);
 265                         if (!ret)
 266                                 break;
 267                 }
 268
 269                 if (ret)
 270                         goto err;
 271         }
 272
 273         ret = IIO_VAL_INT;
 274         if (chan->type == IIO_TEMP)
 275                 *val = dht11->temperature;
 276         else if (chan->type == IIO_HUMIDITYRELATIVE)
 277                 *val = dht11->humidity;
 278         else
 279                 ret = -EINVAL;
 280 err:
 281         dht11->num_edges = -1;
 282         mutex_unlock(&dht11->lock);
 283         return ret;
 284 }
 285
 286 static const struct iio_info dht11_iio_info = {
 287         .driver_module          = THIS_MODULE,
 288         .read_raw               = dht11_read_raw,
 289 };
 290
 291 static const struct iio_chan_spec dht11_chan_spec[] = {
 292         { .type = IIO_TEMP,
 293                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
 294         { .type = IIO_HUMIDITYRELATIVE,
 295                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
 296 };
 297
 298 static const struct of_device_id dht11_dt_ids[] = {
 299         { .compatible = "dht11", },
 300         { }
 301 };
 302 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
 303
 304 static int dht11_probe(struct platform_device *pdev)
 305 {
 306         struct device *dev = &pdev->dev;
 307         struct device_node *node = dev->of_node;
 308         struct dht11 *dht11;
 309         struct iio_dev *iio;
 310         int ret;
 311
 312         iio = devm_iio_device_alloc(dev, sizeof(*dht11));
 313         if (!iio) {
 314                 dev_err(dev, "Failed to allocate IIO device\n");
 315                 return -ENOMEM;
 316         }
 317
 318         dht11 = iio_priv(iio);
 319         dht11->dev = dev;
 320
 321         ret = of_get_gpio(node, 0);
 322         if (ret < 0)
 323                 return ret;
 324         dht11->gpio = ret;
 325         ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
 326         if (ret)
 327                 return ret;
 328
 329         dht11->irq = gpio_to_irq(dht11->gpio);
 330         if (dht11->irq < 0) {
 331                 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
 332                 return -EINVAL;
 333         }
 334
 335         dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1;
 336         dht11->num_edges = -1;
 337
 338         platform_set_drvdata(pdev, iio);
 339
 340         init_completion(&dht11->completion);
 341         mutex_init(&dht11->lock);
 342         iio->name = pdev->name;
 343         iio->dev.parent = &pdev->dev;
 344         iio->info = &dht11_iio_info;
 345         iio->modes = INDIO_DIRECT_MODE;
 346         iio->channels = dht11_chan_spec;
 347         iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
 348
 349         return devm_iio_device_register(dev, iio);
 350 }
 351
 352 static struct platform_driver dht11_driver = {
 353         .driver = {
 354                 .name   = DRIVER_NAME,
 355                 .of_match_table = dht11_dt_ids,
 356         },
 357         .probe  = dht11_probe,
 358 };
 359
 360 module_platform_driver(dht11_driver);
 361
 362 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
 363 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
 364 MODULE_LICENSE("GPL v2");