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/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
  53 struct 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
  70 static 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
  84 static 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
 141 static 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;
 186 err:
 187         dht11->num_edges = -1;
 188         return ret;
 189 }
 190
 191 static 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 */
 199 static 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
 217 static 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
 224 static const struct of_device_id dht11_dt_ids[] = {
 225         { .compatible = "dht11", },
 226         { }
 227 };
 228 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
 229
 230 static 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
 281 static 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
 289 module_platform_driver(dht11_driver);
 290
 291 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
 292 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
 293 MODULE_LICENSE("GPL v2");