LXR linux/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
  81struct 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 */
 105static 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
 118static 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
 132static 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 */
 182static 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
 200static 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;
 280err:
 281        dht11->num_edges = -1;
 282        mutex_unlock(&dht11->lock);
 283        return ret;
 284}
 285
 286static const struct iio_info dht11_iio_info = {
 287        .read_raw               = dht11_read_raw,
 288};
 289
 290static const struct iio_chan_spec dht11_chan_spec[] = {
 291        { .type = IIO_TEMP,
 292                .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
 293        { .type = IIO_HUMIDITYRELATIVE,
 294                .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
 295};
 296
 297static const struct of_device_id dht11_dt_ids[] = {
 298        { .compatible = "dht11", },
 299        { }
 300};
 301MODULE_DEVICE_TABLE(of, dht11_dt_ids);
 302
 303static int dht11_probe(struct platform_device *pdev)
 304{
 305        struct device *dev = &pdev->dev;
 306        struct device_node *node = dev->of_node;
 307        struct dht11 *dht11;
 308        struct iio_dev *iio;
 309        int ret;
 310
 311        iio = devm_iio_device_alloc(dev, sizeof(*dht11));
 312        if (!iio) {
 313                dev_err(dev, "Failed to allocate IIO device\n");
 314                return -ENOMEM;
 315        }
 316
 317        dht11 = iio_priv(iio);
 318        dht11->dev = dev;
 319
 320        ret = of_get_gpio(node, 0);
 321        if (ret < 0)
 322                return ret;
 323        dht11->gpio = ret;
 324        ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
 325        if (ret)
 326                return ret;
 327
 328        dht11->irq = gpio_to_irq(dht11->gpio);
 329        if (dht11->irq < 0) {
 330                dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
 331                return -EINVAL;
 332        }
 333
 334        dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1;
 335        dht11->num_edges = -1;
 336
 337        platform_set_drvdata(pdev, iio);
 338
 339        init_completion(&dht11->completion);
 340        mutex_init(&dht11->lock);
 341        iio->name = pdev->name;
 342        iio->dev.parent = &pdev->dev;
 343        iio->info = &dht11_iio_info;
 344        iio->modes = INDIO_DIRECT_MODE;
 345        iio->channels = dht11_chan_spec;
 346        iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
 347
 348        return devm_iio_device_register(dev, iio);
 349}
 350
 351static struct platform_driver dht11_driver = {
 352        .driver = {
 353                .name   = DRIVER_NAME,
 354                .of_match_table = dht11_dt_ids,
 355        },
 356        .probe  = dht11_probe,
 357};
 358
 359module_platform_driver(dht11_driver);
 360
 361MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
 362MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
 363MODULE_LICENSE("GPL v2");
 364