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