drivers/iio/humidity/dht11.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * DHT11/DHT22 bit banging GPIO driver
   4  *
   5  * Copyright (c) Harald Geyer <harald@ccbib.org>
   6  */
   7
   8 #include <linux/err.h>
   9 #include <linux/interrupt.h>
  10 #include <linux/device.h>
  11 #include <linux/kernel.h>
  12 #include <linux/printk.h>
  13 #include <linux/slab.h>
  14 #include <linux/of.h>
  15 #include <linux/of_device.h>
  16 #include <linux/sysfs.h>
  17 #include <linux/io.h>
  18 #include <linux/module.h>
  19 #include <linux/platform_device.h>
  20 #include <linux/wait.h>
  21 #include <linux/bitops.h>
  22 #include <linux/completion.h>
  23 #include <linux/mutex.h>
  24 #include <linux/delay.h>
  25 #include <linux/gpio.h>
  26 #include <linux/of_gpio.h>
  27 #include <linux/timekeeping.h>
  28
  29 #include <linux/iio/iio.h>
  30
  31 #define DRIVER_NAME     "dht11"
  32
  33 #define DHT11_DATA_VALID_TIME   2000000000  /* 2s in ns */
  34
  35 #define DHT11_EDGES_PREAMBLE 2
  36 #define DHT11_BITS_PER_READ 40
  37 /*
  38  * Note that when reading the sensor actually 84 edges are detected, but
  39  * since the last edge is not significant, we only store 83:
  40  */
  41 #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \
  42                               DHT11_EDGES_PREAMBLE + 1)
  43
  44 /*
  45  * Data transmission timing:
  46  * Data bits are encoded as pulse length (high time) on the data line.
  47  * 0-bit: 22-30uS -- typically 26uS (AM2302)
  48  * 1-bit: 68-75uS -- typically 70uS (AM2302)
  49  * The acutal timings also depend on the properties of the cable, with
  50  * longer cables typically making pulses shorter.
  51  *
  52  * Our decoding depends on the time resolution of the system:
  53  * timeres > 34uS ... don't know what a 1-tick pulse is
  54  * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks)
  55  * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is
  56  * timeres < 23uS ... no problem
  57  *
  58  * Luckily clocks in the 33-44kHz range are quite uncommon, so we can
  59  * support most systems if the threshold for decoding a pulse as 1-bit
  60  * is chosen carefully. If somebody really wants to support clocks around
  61  * 40kHz, where this driver is most unreliable, there are two options.
  62  * a) select an implementation using busy loop polling on those systems
  63  * b) use the checksum to do some probabilistic decoding
  64  */
  65 #define DHT11_START_TRANSMISSION_MIN    18000  /* us */
  66 #define DHT11_START_TRANSMISSION_MAX    20000  /* us */
  67 #define DHT11_MIN_TIMERES       34000  /* ns */
  68 #define DHT11_THRESHOLD         49000  /* ns */
  69 #define DHT11_AMBIG_LOW         23000  /* ns */
  70 #define DHT11_AMBIG_HIGH        30000  /* ns */
  71
  72 struct dht11 {
  73         struct device                   *dev;
  74
  75         int                             gpio;
  76         int                             irq;
  77
  78         struct completion               completion;
  79         /* The iio sysfs interface doesn't prevent concurrent reads: */
  80         struct mutex                    lock;
  81
  82         s64                             timestamp;
  83         int                             temperature;
  84         int                             humidity;
  85
  86         /* num_edges: -1 means "no transmission in progress" */
  87         int                             num_edges;
  88         struct {s64 ts; int value; }    edges[DHT11_EDGES_PER_READ];
  89 };
  90
  91 #ifdef CONFIG_DYNAMIC_DEBUG
  92 /*
  93  * dht11_edges_print: show the data as actually received by the
  94  *                    driver.
  95  */
  96 static void dht11_edges_print(struct dht11 *dht11)
  97 {
  98         int i;
  99
 100         dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);
 101         for (i = 1; i < dht11->num_edges; ++i) {
 102                 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
 103                         dht11->edges[i].ts - dht11->edges[i - 1].ts,
 104                         dht11->edges[i - 1].value ? "high" : "low");
 105         }
 106 }
 107 #endif /* CONFIG_DYNAMIC_DEBUG */
 108
 109 static unsigned char dht11_decode_byte(char *bits)
 110 {
 111         unsigned char ret = 0;
 112         int i;
 113
 114         for (i = 0; i < 8; ++i) {
 115                 ret <<= 1;
 116                 if (bits[i])
 117                         ++ret;
 118         }
 119
 120         return ret;
 121 }
 122
 123 static int dht11_decode(struct dht11 *dht11, int offset)
 124 {
 125         int i, t;
 126         char bits[DHT11_BITS_PER_READ];
 127         unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
 128
 129         for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
 130                 t = dht11->edges[offset + 2 * i + 2].ts -
 131                         dht11->edges[offset + 2 * i + 1].ts;
 132                 if (!dht11->edges[offset + 2 * i + 1].value) {
 133                         dev_dbg(dht11->dev,
 134                                 "lost synchronisation at edge %d\n",
 135                                 offset + 2 * i + 1);
 136                         return -EIO;
 137                 }
 138                 bits[i] = t > DHT11_THRESHOLD;
 139         }
 140
 141         hum_int = dht11_decode_byte(bits);
 142         hum_dec = dht11_decode_byte(&bits[8]);
 143         temp_int = dht11_decode_byte(&bits[16]);
 144         temp_dec = dht11_decode_byte(&bits[24]);
 145         checksum = dht11_decode_byte(&bits[32]);
 146
 147         if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {
 148                 dev_dbg(dht11->dev, "invalid checksum\n");
 149                 return -EIO;
 150         }
 151
 152         dht11->timestamp = ktime_get_boot_ns();
 153         if (hum_int < 4) {  /* DHT22: 100000 = (3*256+232)*100 */
 154                 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
 155                                         ((temp_int & 0x80) ? -100 : 100);
 156                 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
 157         } else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
 158                 dht11->temperature = temp_int * 1000;
 159                 dht11->humidity = hum_int * 1000;
 160         } else {
 161                 dev_err(dht11->dev,
 162                         "Don't know how to decode data: %d %d %d %d\n",
 163                         hum_int, hum_dec, temp_int, temp_dec);
 164                 return -EIO;
 165         }
 166
 167         return 0;
 168 }
 169
 170 /*
 171  * IRQ handler called on GPIO edges
 172  */
 173 static irqreturn_t dht11_handle_irq(int irq, void *data)
 174 {
 175         struct iio_dev *iio = data;
 176         struct dht11 *dht11 = iio_priv(iio);
 177
 178         /* TODO: Consider making the handler safe for IRQ sharing */
 179         if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
 180                 dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns();
 181                 dht11->edges[dht11->num_edges++].value =
 182                                                 gpio_get_value(dht11->gpio);
 183
 184                 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
 185                         complete(&dht11->completion);
 186         }
 187
 188         return IRQ_HANDLED;
 189 }
 190
 191 static int dht11_read_raw(struct iio_dev *iio_dev,
 192                           const struct iio_chan_spec *chan,
 193                         int *val, int *val2, long m)
 194 {
 195         struct dht11 *dht11 = iio_priv(iio_dev);
 196         int ret, timeres, offset;
 197
 198         mutex_lock(&dht11->lock);
 199         if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) {
 200                 timeres = ktime_get_resolution_ns();
 201                 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);
 202                 if (timeres > DHT11_MIN_TIMERES) {
 203                         dev_err(dht11->dev, "timeresolution %dns too low\n",
 204                                 timeres);
 205                         /* In theory a better clock could become available
 206                          * at some point ... and there is no error code
 207                          * that really fits better.
 208                          */
 209                         ret = -EAGAIN;
 210                         goto err;
 211                 }
 212                 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)
 213                         dev_warn(dht11->dev,
 214                                  "timeresolution: %dns - decoding ambiguous\n",
 215                                  timeres);
 216
 217                 reinit_completion(&dht11->completion);
 218
 219                 dht11->num_edges = 0;
 220                 ret = gpio_direction_output(dht11->gpio, 0);
 221                 if (ret)
 222                         goto err;
 223                 usleep_range(DHT11_START_TRANSMISSION_MIN,
 224                              DHT11_START_TRANSMISSION_MAX);
 225                 ret = gpio_direction_input(dht11->gpio);
 226                 if (ret)
 227                         goto err;
 228
 229                 ret = request_irq(dht11->irq, dht11_handle_irq,
 230                                   IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
 231                                   iio_dev->name, iio_dev);
 232                 if (ret)
 233                         goto err;
 234
 235                 ret = wait_for_completion_killable_timeout(&dht11->completion,
 236                                                            HZ);
 237
 238                 free_irq(dht11->irq, iio_dev);
 239
 240 #ifdef CONFIG_DYNAMIC_DEBUG
 241                 dht11_edges_print(dht11);
 242 #endif
 243
 244                 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
 245                         dev_err(dht11->dev, "Only %d signal edges detected\n",
 246                                 dht11->num_edges);
 247                         ret = -ETIMEDOUT;
 248                 }
 249                 if (ret < 0)
 250                         goto err;
 251
 252                 offset = DHT11_EDGES_PREAMBLE +
 253                                 dht11->num_edges - DHT11_EDGES_PER_READ;
 254                 for (; offset >= 0; --offset) {
 255                         ret = dht11_decode(dht11, offset);
 256                         if (!ret)
 257                                 break;
 258                 }
 259
 260                 if (ret)
 261                         goto err;
 262         }
 263
 264         ret = IIO_VAL_INT;
 265         if (chan->type == IIO_TEMP)
 266                 *val = dht11->temperature;
 267         else if (chan->type == IIO_HUMIDITYRELATIVE)
 268                 *val = dht11->humidity;
 269         else
 270                 ret = -EINVAL;
 271 err:
 272         dht11->num_edges = -1;
 273         mutex_unlock(&dht11->lock);
 274         return ret;
 275 }
 276
 277 static const struct iio_info dht11_iio_info = {
 278         .read_raw               = dht11_read_raw,
 279 };
 280
 281 static const struct iio_chan_spec dht11_chan_spec[] = {
 282         { .type = IIO_TEMP,
 283                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
 284         { .type = IIO_HUMIDITYRELATIVE,
 285                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
 286 };
 287
 288 static const struct of_device_id dht11_dt_ids[] = {
 289         { .compatible = "dht11", },
 290         { }
 291 };
 292 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
 293
 294 static int dht11_probe(struct platform_device *pdev)
 295 {
 296         struct device *dev = &pdev->dev;
 297         struct device_node *node = dev->of_node;
 298         struct dht11 *dht11;
 299         struct iio_dev *iio;
 300         int ret;
 301
 302         iio = devm_iio_device_alloc(dev, sizeof(*dht11));
 303         if (!iio) {
 304                 dev_err(dev, "Failed to allocate IIO device\n");
 305                 return -ENOMEM;
 306         }
 307
 308         dht11 = iio_priv(iio);
 309         dht11->dev = dev;
 310
 311         ret = of_get_gpio(node, 0);
 312         if (ret < 0)
 313                 return ret;
 314         dht11->gpio = ret;
 315         ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
 316         if (ret)
 317                 return ret;
 318
 319         dht11->irq = gpio_to_irq(dht11->gpio);
 320         if (dht11->irq < 0) {
 321                 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
 322                 return -EINVAL;
 323         }
 324
 325         dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1;
 326         dht11->num_edges = -1;
 327
 328         platform_set_drvdata(pdev, iio);
 329
 330         init_completion(&dht11->completion);
 331         mutex_init(&dht11->lock);
 332         iio->name = pdev->name;
 333         iio->dev.parent = &pdev->dev;
 334         iio->info = &dht11_iio_info;
 335         iio->modes = INDIO_DIRECT_MODE;
 336         iio->channels = dht11_chan_spec;
 337         iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
 338
 339         return devm_iio_device_register(dev, iio);
 340 }
 341
 342 static struct platform_driver dht11_driver = {
 343         .driver = {
 344                 .name   = DRIVER_NAME,
 345                 .of_match_table = dht11_dt_ids,
 346         },
 347         .probe  = dht11_probe,
 348 };
 349
 350 module_platform_driver(dht11_driver);
 351
 352 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
 353 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
 354 MODULE_LICENSE("GPL v2");