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
  37 #include <linux/iio/iio.h>
  38
  39 #define DRIVER_NAME     "dht11"
  40
  41 #define DHT11_DATA_VALID_TIME   2000000000  /* 2s in ns */
  42
  43 #define DHT11_EDGES_PREAMBLE 2
  44 #define DHT11_BITS_PER_READ 40
  45 /*
  46  * Note that when reading the sensor actually 84 edges are detected, but
  47  * since the last edge is not significant, we only store 83:
  48  */
  49 #define DHT11_EDGES_PER_READ (2*DHT11_BITS_PER_READ + DHT11_EDGES_PREAMBLE + 1)
  50
  51 /* Data transmission timing (nano seconds) */
  52 #define DHT11_START_TRANSMISSION        18  /* ms */
  53 #define DHT11_SENSOR_RESPONSE   80000
  54 #define DHT11_START_BIT         50000
  55 #define DHT11_DATA_BIT_LOW      27000
  56 #define DHT11_DATA_BIT_HIGH     70000
  57
  58 struct dht11 {
  59         struct device                   *dev;
  60
  61         int                             gpio;
  62         int                             irq;
  63
  64         struct completion               completion;
  65         struct mutex                    lock;
  66
  67         s64                             timestamp;
  68         int                             temperature;
  69         int                             humidity;
  70
  71         /* num_edges: -1 means "no transmission in progress" */
  72         int                             num_edges;
  73         struct {s64 ts; int value; }    edges[DHT11_EDGES_PER_READ];
  74 };
  75
  76 static unsigned char dht11_decode_byte(int *timing, int threshold)
  77 {
  78         unsigned char ret = 0;
  79         int i;
  80
  81         for (i = 0; i < 8; ++i) {
  82                 ret <<= 1;
  83                 if (timing[i] >= threshold)
  84                         ++ret;
  85         }
  86
  87         return ret;
  88 }
  89
  90 static int dht11_decode(struct dht11 *dht11, int offset)
  91 {
  92         int i, t, timing[DHT11_BITS_PER_READ], threshold,
  93                 timeres = DHT11_SENSOR_RESPONSE;
  94         unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
  95
  96         /* Calculate timestamp resolution */
  97         for (i = 1; i < dht11->num_edges; ++i) {
  98                 t = dht11->edges[i].ts - dht11->edges[i-1].ts;
  99                 if (t > 0 && t < timeres)
 100                         timeres = t;
 101         }
 102         if (2*timeres > DHT11_DATA_BIT_HIGH) {
 103                 pr_err("dht11: timeresolution %d too bad for decoding\n",
 104                         timeres);
 105                 return -EIO;
 106         }
 107         threshold = DHT11_DATA_BIT_HIGH / timeres;
 108         if (DHT11_DATA_BIT_LOW/timeres + 1 >= threshold)
 109                 pr_err("dht11: WARNING: decoding ambiguous\n");
 110
 111         /* scale down with timeres and check validity */
 112         for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
 113                 t = dht11->edges[offset + 2*i + 2].ts -
 114                         dht11->edges[offset + 2*i + 1].ts;
 115                 if (!dht11->edges[offset + 2*i + 1].value)
 116                         return -EIO;  /* lost synchronisation */
 117                 timing[i] = t / timeres;
 118         }
 119
 120         hum_int = dht11_decode_byte(timing, threshold);
 121         hum_dec = dht11_decode_byte(&timing[8], threshold);
 122         temp_int = dht11_decode_byte(&timing[16], threshold);
 123         temp_dec = dht11_decode_byte(&timing[24], threshold);
 124         checksum = dht11_decode_byte(&timing[32], threshold);
 125
 126         if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum)
 127                 return -EIO;
 128
 129         dht11->timestamp = iio_get_time_ns();
 130         if (hum_int < 20) {  /* DHT22 */
 131                 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
 132                                         ((temp_int & 0x80) ? -100 : 100);
 133                 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
 134         } else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
 135                 dht11->temperature = temp_int * 1000;
 136                 dht11->humidity = hum_int * 1000;
 137         } else {
 138                 dev_err(dht11->dev,
 139                         "Don't know how to decode data: %d %d %d %d\n",
 140                         hum_int, hum_dec, temp_int, temp_dec);
 141                 return -EIO;
 142         }
 143
 144         return 0;
 145 }
 146
 147 /*
 148  * IRQ handler called on GPIO edges
 149  */
 150 static irqreturn_t dht11_handle_irq(int irq, void *data)
 151 {
 152         struct iio_dev *iio = data;
 153         struct dht11 *dht11 = iio_priv(iio);
 154
 155         /* TODO: Consider making the handler safe for IRQ sharing */
 156         if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
 157                 dht11->edges[dht11->num_edges].ts = iio_get_time_ns();
 158                 dht11->edges[dht11->num_edges++].value =
 159                                                 gpio_get_value(dht11->gpio);
 160
 161                 if (dht11->num_edges >= DHT11_EDGES_PER_READ)
 162                         complete(&dht11->completion);
 163         }
 164
 165         return IRQ_HANDLED;
 166 }
 167
 168 static int dht11_read_raw(struct iio_dev *iio_dev,
 169                         const struct iio_chan_spec *chan,
 170                         int *val, int *val2, long m)
 171 {
 172         struct dht11 *dht11 = iio_priv(iio_dev);
 173         int ret;
 174
 175         mutex_lock(&dht11->lock);
 176         if (dht11->timestamp + DHT11_DATA_VALID_TIME < iio_get_time_ns()) {
 177                 reinit_completion(&dht11->completion);
 178
 179                 dht11->num_edges = 0;
 180                 ret = gpio_direction_output(dht11->gpio, 0);
 181                 if (ret)
 182                         goto err;
 183                 msleep(DHT11_START_TRANSMISSION);
 184                 ret = gpio_direction_input(dht11->gpio);
 185                 if (ret)
 186                         goto err;
 187
 188                 ret = request_irq(dht11->irq, dht11_handle_irq,
 189                                   IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
 190                                   iio_dev->name, iio_dev);
 191                 if (ret)
 192                         goto err;
 193
 194                 ret = wait_for_completion_killable_timeout(&dht11->completion,
 195                                                                  HZ);
 196
 197                 free_irq(dht11->irq, iio_dev);
 198
 199                 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
 200                         dev_err(&iio_dev->dev,
 201                                         "Only %d signal edges detected\n",
 202                                         dht11->num_edges);
 203                         ret = -ETIMEDOUT;
 204                 }
 205                 if (ret < 0)
 206                         goto err;
 207
 208                 ret = dht11_decode(dht11,
 209                                 dht11->num_edges == DHT11_EDGES_PER_READ ?
 210                                         DHT11_EDGES_PREAMBLE :
 211                                         DHT11_EDGES_PREAMBLE - 2);
 212                 if (ret)
 213                         goto err;
 214         }
 215
 216         ret = IIO_VAL_INT;
 217         if (chan->type == IIO_TEMP)
 218                 *val = dht11->temperature;
 219         else if (chan->type == IIO_HUMIDITYRELATIVE)
 220                 *val = dht11->humidity;
 221         else
 222                 ret = -EINVAL;
 223 err:
 224         dht11->num_edges = -1;
 225         mutex_unlock(&dht11->lock);
 226         return ret;
 227 }
 228
 229 static const struct iio_info dht11_iio_info = {
 230         .driver_module          = THIS_MODULE,
 231         .read_raw               = dht11_read_raw,
 232 };
 233
 234 static const struct iio_chan_spec dht11_chan_spec[] = {
 235         { .type = IIO_TEMP,
 236                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
 237         { .type = IIO_HUMIDITYRELATIVE,
 238                 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
 239 };
 240
 241 static const struct of_device_id dht11_dt_ids[] = {
 242         { .compatible = "dht11", },
 243         { }
 244 };
 245 MODULE_DEVICE_TABLE(of, dht11_dt_ids);
 246
 247 static int dht11_probe(struct platform_device *pdev)
 248 {
 249         struct device *dev = &pdev->dev;
 250         struct device_node *node = dev->of_node;
 251         struct dht11 *dht11;
 252         struct iio_dev *iio;
 253         int ret;
 254
 255         iio = devm_iio_device_alloc(dev, sizeof(*dht11));
 256         if (!iio) {
 257                 dev_err(dev, "Failed to allocate IIO device\n");
 258                 return -ENOMEM;
 259         }
 260
 261         dht11 = iio_priv(iio);
 262         dht11->dev = dev;
 263
 264         dht11->gpio = ret = of_get_gpio(node, 0);
 265         if (ret < 0)
 266                 return ret;
 267         ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
 268         if (ret)
 269                 return ret;
 270
 271         dht11->irq = gpio_to_irq(dht11->gpio);
 272         if (dht11->irq < 0) {
 273                 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
 274                 return -EINVAL;
 275         }
 276
 277         dht11->timestamp = iio_get_time_ns() - DHT11_DATA_VALID_TIME - 1;
 278         dht11->num_edges = -1;
 279
 280         platform_set_drvdata(pdev, iio);
 281
 282         init_completion(&dht11->completion);
 283         mutex_init(&dht11->lock);
 284         iio->name = pdev->name;
 285         iio->dev.parent = &pdev->dev;
 286         iio->info = &dht11_iio_info;
 287         iio->modes = INDIO_DIRECT_MODE;
 288         iio->channels = dht11_chan_spec;
 289         iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
 290
 291         return devm_iio_device_register(dev, iio);
 292 }
 293
 294 static struct platform_driver dht11_driver = {
 295         .driver = {
 296                 .name   = DRIVER_NAME,
 297                 .of_match_table = dht11_dt_ids,
 298         },
 299         .probe  = dht11_probe,
 300 };
 301
 302 module_platform_driver(dht11_driver);
 303
 304 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
 305 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
 306 MODULE_LICENSE("GPL v2");