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 18 /* ms */ 75 #define DHT11_MIN_TIMERES 34000 /* ns */ 76 #define DHT11_THRESHOLD 49000 /* ns */ 77 #define DHT11_AMBIG_LOW 23000 /* ns */ 78 #define DHT11_AMBIG_HIGH 30000 /* ns */ 79 80 struct dht11 { 81 struct device *dev; 82 83 int gpio; 84 int irq; 85 86 struct completion completion; 87 /* The iio sysfs interface doesn't prevent concurrent reads: */ 88 struct mutex lock; 89 90 s64 timestamp; 91 int temperature; 92 int humidity; 93 94 /* num_edges: -1 means "no transmission in progress" */ 95 int num_edges; 96 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; 97 }; 98 99 static unsigned char dht11_decode_byte(char *bits) 100 { 101 unsigned char ret = 0; 102 int i; 103 104 for (i = 0; i < 8; ++i) { 105 ret <<= 1; 106 if (bits[i]) 107 ++ret; 108 } 109 110 return ret; 111 } 112 113 static int dht11_decode(struct dht11 *dht11, int offset) 114 { 115 int i, t; 116 char bits[DHT11_BITS_PER_READ]; 117 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; 118 119 for (i = 0; i < DHT11_BITS_PER_READ; ++i) { 120 t = dht11->edges[offset + 2 * i + 2].ts - 121 dht11->edges[offset + 2 * i + 1].ts; 122 if (!dht11->edges[offset + 2 * i + 1].value) 123 return -EIO; /* lost synchronisation */ 124 bits[i] = t > DHT11_THRESHOLD; 125 } 126 127 hum_int = dht11_decode_byte(bits); 128 hum_dec = dht11_decode_byte(&bits[8]); 129 temp_int = dht11_decode_byte(&bits[16]); 130 temp_dec = dht11_decode_byte(&bits[24]); 131 checksum = dht11_decode_byte(&bits[32]); 132 133 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) 134 return -EIO; 135 136 dht11->timestamp = ktime_get_boot_ns(); 137 if (hum_int < 20) { /* DHT22 */ 138 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * 139 ((temp_int & 0x80) ? -100 : 100); 140 dht11->humidity = ((hum_int << 8) + hum_dec) * 100; 141 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ 142 dht11->temperature = temp_int * 1000; 143 dht11->humidity = hum_int * 1000; 144 } else { 145 dev_err(dht11->dev, 146 "Don't know how to decode data: %d %d %d %d\n", 147 hum_int, hum_dec, temp_int, temp_dec); 148 return -EIO; 149 } 150 151 return 0; 152 } 153 154 /* 155 * IRQ handler called on GPIO edges 156 */ 157 static irqreturn_t dht11_handle_irq(int irq, void *data) 158 { 159 struct iio_dev *iio = data; 160 struct dht11 *dht11 = iio_priv(iio); 161 162 /* TODO: Consider making the handler safe for IRQ sharing */ 163 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { 164 dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns(); 165 dht11->edges[dht11->num_edges++].value = 166 gpio_get_value(dht11->gpio); 167 168 if (dht11->num_edges >= DHT11_EDGES_PER_READ) 169 complete(&dht11->completion); 170 } 171 172 return IRQ_HANDLED; 173 } 174 175 static int dht11_read_raw(struct iio_dev *iio_dev, 176 const struct iio_chan_spec *chan, 177 int *val, int *val2, long m) 178 { 179 struct dht11 *dht11 = iio_priv(iio_dev); 180 int ret, timeres, offset; 181 182 mutex_lock(&dht11->lock); 183 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) { 184 timeres = ktime_get_resolution_ns(); 185 if (timeres > DHT11_MIN_TIMERES) { 186 dev_err(dht11->dev, "timeresolution %dns too low\n", 187 timeres); 188 /* In theory a better clock could become available 189 * at some point ... and there is no error code 190 * that really fits better. 191 */ 192 ret = -EAGAIN; 193 goto err; 194 } 195 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH) 196 dev_warn(dht11->dev, 197 "timeresolution: %dns - decoding ambiguous\n", 198 timeres); 199 200 reinit_completion(&dht11->completion); 201 202 dht11->num_edges = 0; 203 ret = gpio_direction_output(dht11->gpio, 0); 204 if (ret) 205 goto err; 206 msleep(DHT11_START_TRANSMISSION); 207 ret = gpio_direction_input(dht11->gpio); 208 if (ret) 209 goto err; 210 211 ret = request_irq(dht11->irq, dht11_handle_irq, 212 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, 213 iio_dev->name, iio_dev); 214 if (ret) 215 goto err; 216 217 ret = wait_for_completion_killable_timeout(&dht11->completion, 218 HZ); 219 220 free_irq(dht11->irq, iio_dev); 221 222 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { 223 dev_err(&iio_dev->dev, 224 "Only %d signal edges detected\n", 225 dht11->num_edges); 226 ret = -ETIMEDOUT; 227 } 228 if (ret < 0) 229 goto err; 230 231 offset = DHT11_EDGES_PREAMBLE + 232 dht11->num_edges - DHT11_EDGES_PER_READ; 233 for (; offset >= 0; --offset) { 234 ret = dht11_decode(dht11, offset); 235 if (!ret) 236 break; 237 } 238 239 if (ret) 240 goto err; 241 } 242 243 ret = IIO_VAL_INT; 244 if (chan->type == IIO_TEMP) 245 *val = dht11->temperature; 246 else if (chan->type == IIO_HUMIDITYRELATIVE) 247 *val = dht11->humidity; 248 else 249 ret = -EINVAL; 250 err: 251 dht11->num_edges = -1; 252 mutex_unlock(&dht11->lock); 253 return ret; 254 } 255 256 static const struct iio_info dht11_iio_info = { 257 .driver_module = THIS_MODULE, 258 .read_raw = dht11_read_raw, 259 }; 260 261 static const struct iio_chan_spec dht11_chan_spec[] = { 262 { .type = IIO_TEMP, 263 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, 264 { .type = IIO_HUMIDITYRELATIVE, 265 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } 266 }; 267 268 static const struct of_device_id dht11_dt_ids[] = { 269 { .compatible = "dht11", }, 270 { } 271 }; 272 MODULE_DEVICE_TABLE(of, dht11_dt_ids); 273 274 static int dht11_probe(struct platform_device *pdev) 275 { 276 struct device *dev = &pdev->dev; 277 struct device_node *node = dev->of_node; 278 struct dht11 *dht11; 279 struct iio_dev *iio; 280 int ret; 281 282 iio = devm_iio_device_alloc(dev, sizeof(*dht11)); 283 if (!iio) { 284 dev_err(dev, "Failed to allocate IIO device\n"); 285 return -ENOMEM; 286 } 287 288 dht11 = iio_priv(iio); 289 dht11->dev = dev; 290 291 ret = of_get_gpio(node, 0); 292 if (ret < 0) 293 return ret; 294 dht11->gpio = ret; 295 ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name); 296 if (ret) 297 return ret; 298 299 dht11->irq = gpio_to_irq(dht11->gpio); 300 if (dht11->irq < 0) { 301 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio); 302 return -EINVAL; 303 } 304 305 dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1; 306 dht11->num_edges = -1; 307 308 platform_set_drvdata(pdev, iio); 309 310 init_completion(&dht11->completion); 311 mutex_init(&dht11->lock); 312 iio->name = pdev->name; 313 iio->dev.parent = &pdev->dev; 314 iio->info = &dht11_iio_info; 315 iio->modes = INDIO_DIRECT_MODE; 316 iio->channels = dht11_chan_spec; 317 iio->num_channels = ARRAY_SIZE(dht11_chan_spec); 318 319 return devm_iio_device_register(dev, iio); 320 } 321 322 static struct platform_driver dht11_driver = { 323 .driver = { 324 .name = DRIVER_NAME, 325 .of_match_table = dht11_dt_ids, 326 }, 327 .probe = dht11_probe, 328 }; 329 330 module_platform_driver(dht11_driver); 331 332 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); 333 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); 334 MODULE_LICENSE("GPL v2"); 335