linux/drivers/iio/humidity/dht11.c
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   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/delay.h>
  33#include <linux/gpio.h>
  34#include <linux/of_gpio.h>
  35
  36#include <linux/iio/iio.h>
  37
  38#define DRIVER_NAME     "dht11"
  39
  40#define DHT11_DATA_VALID_TIME   2000000000  /* 2s in ns */
  41
  42#define DHT11_EDGES_PREAMBLE 4
  43#define DHT11_BITS_PER_READ 40
  44#define DHT11_EDGES_PER_READ (2*DHT11_BITS_PER_READ + DHT11_EDGES_PREAMBLE + 1)
  45
  46/* Data transmission timing (nano seconds) */
  47#define DHT11_START_TRANSMISSION        18  /* ms */
  48#define DHT11_SENSOR_RESPONSE   80000
  49#define DHT11_START_BIT         50000
  50#define DHT11_DATA_BIT_LOW      27000
  51#define DHT11_DATA_BIT_HIGH     70000
  52
  53struct dht11 {
  54        struct device                   *dev;
  55
  56        int                             gpio;
  57        int                             irq;
  58
  59        struct completion               completion;
  60
  61        s64                             timestamp;
  62        int                             temperature;
  63        int                             humidity;
  64
  65        /* num_edges: -1 means "no transmission in progress" */
  66        int                             num_edges;
  67        struct {s64 ts; int value; }    edges[DHT11_EDGES_PER_READ];
  68};
  69
  70static unsigned char dht11_decode_byte(int *timing, int threshold)
  71{
  72        unsigned char ret = 0;
  73        int i;
  74
  75        for (i = 0; i < 8; ++i) {
  76                ret <<= 1;
  77                if (timing[i] >= threshold)
  78                        ++ret;
  79        }
  80
  81        return ret;
  82}
  83
  84static int dht11_decode(struct dht11 *dht11, int offset)
  85{
  86        int i, t, timing[DHT11_BITS_PER_READ], threshold,
  87                timeres = DHT11_SENSOR_RESPONSE;
  88        unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
  89
  90        /* Calculate timestamp resolution */
  91        for (i = 0; i < dht11->num_edges; ++i) {
  92                t = dht11->edges[i].ts - dht11->edges[i-1].ts;
  93                if (t > 0 && t < timeres)
  94                        timeres = t;
  95        }
  96        if (2*timeres > DHT11_DATA_BIT_HIGH) {
  97                pr_err("dht11: timeresolution %d too bad for decoding\n",
  98                        timeres);
  99                return -EIO;
 100        }
 101        threshold = DHT11_DATA_BIT_HIGH / timeres;
 102        if (DHT11_DATA_BIT_LOW/timeres + 1 >= threshold)
 103                pr_err("dht11: WARNING: decoding ambiguous\n");
 104
 105        /* scale down with timeres and check validity */
 106        for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
 107                t = dht11->edges[offset + 2*i + 2].ts -
 108                        dht11->edges[offset + 2*i + 1].ts;
 109                if (!dht11->edges[offset + 2*i + 1].value)
 110                        return -EIO;  /* lost synchronisation */
 111                timing[i] = t / timeres;
 112        }
 113
 114        hum_int = dht11_decode_byte(timing, threshold);
 115        hum_dec = dht11_decode_byte(&timing[8], threshold);
 116        temp_int = dht11_decode_byte(&timing[16], threshold);
 117        temp_dec = dht11_decode_byte(&timing[24], threshold);
 118        checksum = dht11_decode_byte(&timing[32], threshold);
 119
 120        if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum)
 121                return -EIO;
 122
 123        dht11->timestamp = iio_get_time_ns();
 124        if (hum_int < 20) {  /* DHT22 */
 125                dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
 126                                        ((temp_int & 0x80) ? -100 : 100);
 127                dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
 128        } else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
 129                dht11->temperature = temp_int * 1000;
 130                dht11->humidity = hum_int * 1000;
 131        } else {
 132                dev_err(dht11->dev,
 133                        "Don't know how to decode data: %d %d %d %d\n",
 134                        hum_int, hum_dec, temp_int, temp_dec);
 135                return -EIO;
 136        }
 137
 138        return 0;
 139}
 140
 141static int dht11_read_raw(struct iio_dev *iio_dev,
 142                        const struct iio_chan_spec *chan,
 143                        int *val, int *val2, long m)
 144{
 145        struct dht11 *dht11 = iio_priv(iio_dev);
 146        int ret;
 147
 148        if (dht11->timestamp + DHT11_DATA_VALID_TIME < iio_get_time_ns()) {
 149                reinit_completion(&dht11->completion);
 150
 151                dht11->num_edges = 0;
 152                ret = gpio_direction_output(dht11->gpio, 0);
 153                if (ret)
 154                        goto err;
 155                msleep(DHT11_START_TRANSMISSION);
 156                ret = gpio_direction_input(dht11->gpio);
 157                if (ret)
 158                        goto err;
 159
 160                ret = wait_for_completion_killable_timeout(&dht11->completion,
 161                                                                 HZ);
 162                if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
 163                        dev_err(&iio_dev->dev,
 164                                        "Only %d signal edges detected\n",
 165                                        dht11->num_edges);
 166                        ret = -ETIMEDOUT;
 167                }
 168                if (ret < 0)
 169                        goto err;
 170
 171                ret = dht11_decode(dht11,
 172                                dht11->num_edges == DHT11_EDGES_PER_READ ?
 173                                        DHT11_EDGES_PREAMBLE :
 174                                        DHT11_EDGES_PREAMBLE - 2);
 175                if (ret)
 176                        goto err;
 177        }
 178
 179        ret = IIO_VAL_INT;
 180        if (chan->type == IIO_TEMP)
 181                *val = dht11->temperature;
 182        else if (chan->type == IIO_HUMIDITYRELATIVE)
 183                *val = dht11->humidity;
 184        else
 185                ret = -EINVAL;
 186err:
 187        dht11->num_edges = -1;
 188        return ret;
 189}
 190
 191static const struct iio_info dht11_iio_info = {
 192        .driver_module          = THIS_MODULE,
 193        .read_raw               = dht11_read_raw,
 194};
 195
 196/*
 197 * IRQ handler called on GPIO edges
 198*/
 199static irqreturn_t dht11_handle_irq(int irq, void *data)
 200{
 201        struct iio_dev *iio = data;
 202        struct dht11 *dht11 = iio_priv(iio);
 203
 204        /* TODO: Consider making the handler safe for IRQ sharing */
 205        if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
 206                dht11->edges[dht11->num_edges].ts = iio_get_time_ns();
 207                dht11->edges[dht11->num_edges++].value =
 208                                                gpio_get_value(dht11->gpio);
 209
 210                if (dht11->num_edges >= DHT11_EDGES_PER_READ)
 211                        complete(&dht11->completion);
 212        }
 213
 214        return IRQ_HANDLED;
 215}
 216
 217static const struct iio_chan_spec dht11_chan_spec[] = {
 218        { .type = IIO_TEMP,
 219                .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
 220        { .type = IIO_HUMIDITYRELATIVE,
 221                .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
 222};
 223
 224static const struct of_device_id dht11_dt_ids[] = {
 225        { .compatible = "dht11", },
 226        { }
 227};
 228MODULE_DEVICE_TABLE(of, dht11_dt_ids);
 229
 230static int dht11_probe(struct platform_device *pdev)
 231{
 232        struct device *dev = &pdev->dev;
 233        struct device_node *node = dev->of_node;
 234        struct dht11 *dht11;
 235        struct iio_dev *iio;
 236        int ret;
 237
 238        iio = devm_iio_device_alloc(dev, sizeof(*dht11));
 239        if (!iio) {
 240                dev_err(dev, "Failed to allocate IIO device\n");
 241                return -ENOMEM;
 242        }
 243
 244        dht11 = iio_priv(iio);
 245        dht11->dev = dev;
 246
 247        dht11->gpio = ret = of_get_gpio(node, 0);
 248        if (ret < 0)
 249                return ret;
 250        ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
 251        if (ret)
 252                return ret;
 253
 254        dht11->irq = gpio_to_irq(dht11->gpio);
 255        if (dht11->irq < 0) {
 256                dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
 257                return -EINVAL;
 258        }
 259        ret = devm_request_irq(dev, dht11->irq, dht11_handle_irq,
 260                                IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
 261                                pdev->name, iio);
 262        if (ret)
 263                return ret;
 264
 265        dht11->timestamp = iio_get_time_ns() - DHT11_DATA_VALID_TIME - 1;
 266        dht11->num_edges = -1;
 267
 268        platform_set_drvdata(pdev, iio);
 269
 270        init_completion(&dht11->completion);
 271        iio->name = pdev->name;
 272        iio->dev.parent = &pdev->dev;
 273        iio->info = &dht11_iio_info;
 274        iio->modes = INDIO_DIRECT_MODE;
 275        iio->channels = dht11_chan_spec;
 276        iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
 277
 278        return devm_iio_device_register(dev, iio);
 279}
 280
 281static struct platform_driver dht11_driver = {
 282        .driver = {
 283                .name   = DRIVER_NAME,
 284                .of_match_table = dht11_dt_ids,
 285        },
 286        .probe  = dht11_probe,
 287};
 288
 289module_platform_driver(dht11_driver);
 290
 291MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
 292MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
 293MODULE_LICENSE("GPL v2");
 294
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