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 #ifdef CONFIG_DYNAMIC_DEBUG 100 /* 101 * dht11_edges_print: show the data as actually received by the 102 * driver. 103 */ 104 static void dht11_edges_print(struct dht11 *dht11) 105 { 106 int i; 107 108 dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges); 109 for (i = 1; i < dht11->num_edges; ++i) { 110 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i, 111 dht11->edges[i].ts - dht11->edges[i - 1].ts, 112 dht11->edges[i - 1].value ? "high" : "low"); 113 } 114 } 115 #endif /* CONFIG_DYNAMIC_DEBUG */ 116 117 static unsigned char dht11_decode_byte(char *bits) 118 { 119 unsigned char ret = 0; 120 int i; 121 122 for (i = 0; i < 8; ++i) { 123 ret <<= 1; 124 if (bits[i]) 125 ++ret; 126 } 127 128 return ret; 129 } 130 131 static int dht11_decode(struct dht11 *dht11, int offset) 132 { 133 int i, t; 134 char bits[DHT11_BITS_PER_READ]; 135 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; 136 137 for (i = 0; i < DHT11_BITS_PER_READ; ++i) { 138 t = dht11->edges[offset + 2 * i + 2].ts - 139 dht11->edges[offset + 2 * i + 1].ts; 140 if (!dht11->edges[offset + 2 * i + 1].value) { 141 dev_dbg(dht11->dev, 142 "lost synchronisation at edge %d\n", 143 offset + 2 * i + 1); 144 return -EIO; 145 } 146 bits[i] = t > DHT11_THRESHOLD; 147 } 148 149 hum_int = dht11_decode_byte(bits); 150 hum_dec = dht11_decode_byte(&bits[8]); 151 temp_int = dht11_decode_byte(&bits[16]); 152 temp_dec = dht11_decode_byte(&bits[24]); 153 checksum = dht11_decode_byte(&bits[32]); 154 155 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) { 156 dev_dbg(dht11->dev, "invalid checksum\n"); 157 return -EIO; 158 } 159 160 dht11->timestamp = ktime_get_boot_ns(); 161 if (hum_int < 20) { /* DHT22 */ 162 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * 163 ((temp_int & 0x80) ? -100 : 100); 164 dht11->humidity = ((hum_int << 8) + hum_dec) * 100; 165 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ 166 dht11->temperature = temp_int * 1000; 167 dht11->humidity = hum_int * 1000; 168 } else { 169 dev_err(dht11->dev, 170 "Don't know how to decode data: %d %d %d %d\n", 171 hum_int, hum_dec, temp_int, temp_dec); 172 return -EIO; 173 } 174 175 return 0; 176 } 177 178 /* 179 * IRQ handler called on GPIO edges 180 */ 181 static irqreturn_t dht11_handle_irq(int irq, void *data) 182 { 183 struct iio_dev *iio = data; 184 struct dht11 *dht11 = iio_priv(iio); 185 186 /* TODO: Consider making the handler safe for IRQ sharing */ 187 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { 188 dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns(); 189 dht11->edges[dht11->num_edges++].value = 190 gpio_get_value(dht11->gpio); 191 192 if (dht11->num_edges >= DHT11_EDGES_PER_READ) 193 complete(&dht11->completion); 194 } 195 196 return IRQ_HANDLED; 197 } 198 199 static int dht11_read_raw(struct iio_dev *iio_dev, 200 const struct iio_chan_spec *chan, 201 int *val, int *val2, long m) 202 { 203 struct dht11 *dht11 = iio_priv(iio_dev); 204 int ret, timeres, offset; 205 206 mutex_lock(&dht11->lock); 207 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) { 208 timeres = ktime_get_resolution_ns(); 209 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres); 210 if (timeres > DHT11_MIN_TIMERES) { 211 dev_err(dht11->dev, "timeresolution %dns too low\n", 212 timeres); 213 /* In theory a better clock could become available 214 * at some point ... and there is no error code 215 * that really fits better. 216 */ 217 ret = -EAGAIN; 218 goto err; 219 } 220 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH) 221 dev_warn(dht11->dev, 222 "timeresolution: %dns - decoding ambiguous\n", 223 timeres); 224 225 reinit_completion(&dht11->completion); 226 227 dht11->num_edges = 0; 228 ret = gpio_direction_output(dht11->gpio, 0); 229 if (ret) 230 goto err; 231 msleep(DHT11_START_TRANSMISSION); 232 ret = gpio_direction_input(dht11->gpio); 233 if (ret) 234 goto err; 235 236 ret = request_irq(dht11->irq, dht11_handle_irq, 237 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, 238 iio_dev->name, iio_dev); 239 if (ret) 240 goto err; 241 242 ret = wait_for_completion_killable_timeout(&dht11->completion, 243 HZ); 244 245 free_irq(dht11->irq, iio_dev); 246 247 #ifdef CONFIG_DYNAMIC_DEBUG 248 dht11_edges_print(dht11); 249 #endif 250 251 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { 252 dev_err(dht11->dev, "Only %d signal edges detected\n", 253 dht11->num_edges); 254 ret = -ETIMEDOUT; 255 } 256 if (ret < 0) 257 goto err; 258 259 offset = DHT11_EDGES_PREAMBLE + 260 dht11->num_edges - DHT11_EDGES_PER_READ; 261 for (; offset >= 0; --offset) { 262 ret = dht11_decode(dht11, offset); 263 if (!ret) 264 break; 265 } 266 267 if (ret) 268 goto err; 269 } 270 271 ret = IIO_VAL_INT; 272 if (chan->type == IIO_TEMP) 273 *val = dht11->temperature; 274 else if (chan->type == IIO_HUMIDITYRELATIVE) 275 *val = dht11->humidity; 276 else 277 ret = -EINVAL; 278 err: 279 dht11->num_edges = -1; 280 mutex_unlock(&dht11->lock); 281 return ret; 282 } 283 284 static const struct iio_info dht11_iio_info = { 285 .driver_module = THIS_MODULE, 286 .read_raw = dht11_read_raw, 287 }; 288 289 static const struct iio_chan_spec dht11_chan_spec[] = { 290 { .type = IIO_TEMP, 291 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, 292 { .type = IIO_HUMIDITYRELATIVE, 293 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } 294 }; 295 296 static const struct of_device_id dht11_dt_ids[] = { 297 { .compatible = "dht11", }, 298 { } 299 }; 300 MODULE_DEVICE_TABLE(of, dht11_dt_ids); 301 302 static int dht11_probe(struct platform_device *pdev) 303 { 304 struct device *dev = &pdev->dev; 305 struct device_node *node = dev->of_node; 306 struct dht11 *dht11; 307 struct iio_dev *iio; 308 int ret; 309 310 iio = devm_iio_device_alloc(dev, sizeof(*dht11)); 311 if (!iio) { 312 dev_err(dev, "Failed to allocate IIO device\n"); 313 return -ENOMEM; 314 } 315 316 dht11 = iio_priv(iio); 317 dht11->dev = dev; 318 319 ret = of_get_gpio(node, 0); 320 if (ret < 0) 321 return ret; 322 dht11->gpio = ret; 323 ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name); 324 if (ret) 325 return ret; 326 327 dht11->irq = gpio_to_irq(dht11->gpio); 328 if (dht11->irq < 0) { 329 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio); 330 return -EINVAL; 331 } 332 333 dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1; 334 dht11->num_edges = -1; 335 336 platform_set_drvdata(pdev, iio); 337 338 init_completion(&dht11->completion); 339 mutex_init(&dht11->lock); 340 iio->name = pdev->name; 341 iio->dev.parent = &pdev->dev; 342 iio->info = &dht11_iio_info; 343 iio->modes = INDIO_DIRECT_MODE; 344 iio->channels = dht11_chan_spec; 345 iio->num_channels = ARRAY_SIZE(dht11_chan_spec); 346 347 return devm_iio_device_register(dev, iio); 348 } 349 350 static struct platform_driver dht11_driver = { 351 .driver = { 352 .name = DRIVER_NAME, 353 .of_match_table = dht11_dt_ids, 354 }, 355 .probe = dht11_probe, 356 }; 357 358 module_platform_driver(dht11_driver); 359 360 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); 361 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); 362 MODULE_LICENSE("GPL v2"); 363