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 #ifdef CONFIG_DYNAMIC_DEBUG
 100 /*
 101  * dht11_edges_print: show the data as actually received by the
 102  *                    driver.
 103  */
 104 static void dht11_edges_print(struct dht11 *dht11)
 105 {
 106         int i;
 107
 108         dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);
 109         for (i = 1; i < dht11->num_edges; ++i) {
 110                 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
 111                         dht11->edges[i].ts - dht11->edges[i - 1].ts,
 112                         dht11->edges[i - 1].value ? "high" : "low");
 113         }
 114 }
 115 #endif /* CONFIG_DYNAMIC_DEBUG */
 116
 117 static unsigned char dht11_decode_byte(char *bits)
 118 {
 119         unsigned char ret = 0;
 120         int i;
 121
 122         for (i = 0; i < 8; ++i) {
 123                 ret <<= 1;
 124                 if (bits[i])
 125                         ++ret;
 126         }
 127
 128         return ret;
 129 }
 130
 131 static int dht11_decode(struct dht11 *dht11, int offset)
 132 {
 133         int i, t;
 134         char bits[DHT11_BITS_PER_READ];
 135         unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
 136
 137         for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
 138                 t = dht11->edges[offset + 2 * i + 2].ts -
 139                         dht11->edges[offset + 2 * i + 1].ts;
 140                 if (!dht11->edges[offset + 2 * i + 1].value) {
 141                         dev_dbg(dht11->dev,
 142                                 "lost synchronisation at edge %d\n",
 143                                 offset + 2 * i + 1);
 144                         return -EIO;
 145                 }
 146                 bits[i] = t > DHT11_THRESHOLD;
 147         }
 148
 149         hum_int = dht11_decode_byte(bits);
 150         hum_dec = dht11_decode_byte(&bits[8]);
 151         temp_int = dht11_decode_byte(&bits[16]);
 152         temp_dec = dht11_decode_byte(&bits[24]);
 153         checksum = dht11_decode_byte(&bits[32]);
 154
 155         if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {
 156                 dev_dbg(dht11->dev, "invalid checksum\n");
 157                 return -EIO;
 158         }
 159
 160         dht11->timestamp = ktime_get_boot_ns();
 161         if (hum_int < 20) {  /* DHT22 */
 162                 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
 163                                         ((temp_int & 0x80) ? -100 : 100);
 164                 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
 165         } else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
 166                 dht11->temperature = temp_int * 1000;
 167                 dht11->humidity = hum_int * 1000;
 168         } else {
 169                 dev_err(dht11->dev,
 170                         "Don't know how to decode data: %d %d %d %d\n",
 171                         hum_int, hum_dec, temp_int, temp_dec);
 172                 return -EIO;
 173         }
 174
 175         return 0;
 176 }
 177
 178 /*
 179  * IRQ handler called on GPIO edges
 180  */
 181 static irqreturn_t dht11_handle_irq(int irq, void *data)
 182 {
 183         struct iio_dev *iio = data;
 184         struct dht11 *dht11 = iio_priv(iio);
 185
 186         /* TODO: Consider making the handler safe for IRQ sharing */
 187         if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
 188                 dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns();
 189                 dht11->edges[dht11->num_edges++].value =
 190                                                 gpio_get_value(dht11->gpio);
 191
 192                 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
 193                         complete(&dht11->completion);
 194         }
 195
 196         return IRQ_HANDLED;
 197 }
 198
 199 static int dht11_read_raw(struct iio_dev *iio_dev,
 200                           const struct iio_chan_spec *chan,
 201                         int *val, int *val2, long m)
 202 {
 203         struct dht11 *dht11 = iio_priv(iio_dev);
 204         int ret, timeres, offset;
 205
 206         mutex_lock(&dht11->lock);
 207         if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) {
 208                 timeres = ktime_get_resolution_ns();
 209                 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);
 210                 if (timeres > DHT11_MIN_TIMERES) {
 211                         dev_err(dht11->dev, "timeresolution %dns too low\n",
 212                                 timeres);
 213                         /* In theory a better clock could become available
 214                          * at some point ... and there is no error code
 215                          * that really fits better.
 216                          */
 217                         ret = -EAGAIN;
 218                         goto err;
 219                 }
 220                 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)
 221                         dev_warn(dht11->dev,
 222                                  "timeresolution: %dns - decoding ambiguous\n",
 223                                  timeres);
 224
 225                 reinit_completion(&dht11->completion);
 226
 227                 dht11->num_edges = 0;
 228                 ret = gpio_direction_output(dht11->gpio, 0);
 229                 if (ret)
 230                         goto err;
 231                 msleep(DHT11_START_TRANSMISSION);
 232                 ret = gpio_direction_input(dht11->gpio);
 233                 if (ret)
 234                         goto err;
 235
 236                 ret = request_irq(dht11->irq, dht11_handle_irq,
 237                                   IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
 238                                   iio_dev->name, iio_dev);
 239                 if (ret)
 240                         goto err;
 241
 242                 ret = wait_for_completion_killable_timeout(&dht11->completion,
 243                                                            HZ);
 244
 245                 free_irq(dht11->irq, iio_dev);
 246
 247 #ifdef CONFIG_DYNAMIC_DEBUG
 248                 dht11_edges_print(dht11);
 249 #endif
 250
 251                 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
 252                         dev_err(dht11->dev, "Only %d signal edges detected\n",
 253                                 dht11->num_edges);
 254                         ret = -ETIMEDOUT;
 255                 }
 256                 if (ret < 0)
 257                         goto err;
 258
 259                 offset = DHT11_EDGES_PREAMBLE +
 260                                 dht11->num_edges - DHT11_EDGES_PER_READ;
 261                 for (; offset >= 0; --offset) {
 262                         ret = dht11_decode(dht11, offset);
 263                         if (!ret)
 264                                 break;
 265                 }
 266
 267                 if (ret)
 268                         goto err;
 269         }
 270
 271         ret = IIO_VAL_INT;
 272         if (chan->type == IIO_TEMP)
 273                 *val = dht11->temperature;
 274         else if (chan->type == IIO_HUMIDITYRELATIVE)
 275                 *val = dht11->humidity;
 276         else
 277                 ret = -EINVAL;
 278 err:
 279         dht11->num_edges = -1;
 280         mutex_unlock(&dht11->lock);
 281         return ret;
 282 }
 283
 284 static const struct iio_info dht11_iio_info = {
 285         .driver_module          = THIS_MODULE,
 286         .read_raw               = dht11_read_raw,
 287 };
 288
 289 static const struct iio_chan_spec dht11_chan_spec[] = {
 290         { .type = IIO_TEMP,
 291                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
 292         { .type = IIO_HUMIDITYRELATIVE,
 293                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
 294 };
 295
 296 static const struct of_device_id dht11_dt_ids[] = {
 297         { .compatible = "dht11", },
 298         { }
 299 };
 300 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
 301
 302 static int dht11_probe(struct platform_device *pdev)
 303 {
 304         struct device *dev = &pdev->dev;
 305         struct device_node *node = dev->of_node;
 306         struct dht11 *dht11;
 307         struct iio_dev *iio;
 308         int ret;
 309
 310         iio = devm_iio_device_alloc(dev, sizeof(*dht11));
 311         if (!iio) {
 312                 dev_err(dev, "Failed to allocate IIO device\n");
 313                 return -ENOMEM;
 314         }
 315
 316         dht11 = iio_priv(iio);
 317         dht11->dev = dev;
 318
 319         ret = of_get_gpio(node, 0);
 320         if (ret < 0)
 321                 return ret;
 322         dht11->gpio = ret;
 323         ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
 324         if (ret)
 325                 return ret;
 326
 327         dht11->irq = gpio_to_irq(dht11->gpio);
 328         if (dht11->irq < 0) {
 329                 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
 330                 return -EINVAL;
 331         }
 332
 333         dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1;
 334         dht11->num_edges = -1;
 335
 336         platform_set_drvdata(pdev, iio);
 337
 338         init_completion(&dht11->completion);
 339         mutex_init(&dht11->lock);
 340         iio->name = pdev->name;
 341         iio->dev.parent = &pdev->dev;
 342         iio->info = &dht11_iio_info;
 343         iio->modes = INDIO_DIRECT_MODE;
 344         iio->channels = dht11_chan_spec;
 345         iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
 346
 347         return devm_iio_device_register(dev, iio);
 348 }
 349
 350 static struct platform_driver dht11_driver = {
 351         .driver = {
 352                 .name   = DRIVER_NAME,
 353                 .of_match_table = dht11_dt_ids,
 354         },
 355         .probe  = dht11_probe,
 356 };
 357
 358 module_platform_driver(dht11_driver);
 359
 360 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
 361 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
 362 MODULE_LICENSE("GPL v2");