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_MIN 18000 /* us */ 75 #define DHT11_START_TRANSMISSION_MAX 20000 /* us */ 76 #define DHT11_MIN_TIMERES 34000 /* ns */ 77 #define DHT11_THRESHOLD 49000 /* ns */ 78 #define DHT11_AMBIG_LOW 23000 /* ns */ 79 #define DHT11_AMBIG_HIGH 30000 /* ns */ 80 81 struct dht11 { 82 struct device *dev; 83 84 int gpio; 85 int irq; 86 87 struct completion completion; 88 /* The iio sysfs interface doesn't prevent concurrent reads: */ 89 struct mutex lock; 90 91 s64 timestamp; 92 int temperature; 93 int humidity; 94 95 /* num_edges: -1 means "no transmission in progress" */ 96 int num_edges; 97 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; 98 }; 99 100 #ifdef CONFIG_DYNAMIC_DEBUG 101 /* 102 * dht11_edges_print: show the data as actually received by the 103 * driver. 104 */ 105 static void dht11_edges_print(struct dht11 *dht11) 106 { 107 int i; 108 109 dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges); 110 for (i = 1; i < dht11->num_edges; ++i) { 111 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i, 112 dht11->edges[i].ts - dht11->edges[i - 1].ts, 113 dht11->edges[i - 1].value ? "high" : "low"); 114 } 115 } 116 #endif /* CONFIG_DYNAMIC_DEBUG */ 117 118 static unsigned char dht11_decode_byte(char *bits) 119 { 120 unsigned char ret = 0; 121 int i; 122 123 for (i = 0; i < 8; ++i) { 124 ret <<= 1; 125 if (bits[i]) 126 ++ret; 127 } 128 129 return ret; 130 } 131 132 static int dht11_decode(struct dht11 *dht11, int offset) 133 { 134 int i, t; 135 char bits[DHT11_BITS_PER_READ]; 136 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; 137 138 for (i = 0; i < DHT11_BITS_PER_READ; ++i) { 139 t = dht11->edges[offset + 2 * i + 2].ts - 140 dht11->edges[offset + 2 * i + 1].ts; 141 if (!dht11->edges[offset + 2 * i + 1].value) { 142 dev_dbg(dht11->dev, 143 "lost synchronisation at edge %d\n", 144 offset + 2 * i + 1); 145 return -EIO; 146 } 147 bits[i] = t > DHT11_THRESHOLD; 148 } 149 150 hum_int = dht11_decode_byte(bits); 151 hum_dec = dht11_decode_byte(&bits[8]); 152 temp_int = dht11_decode_byte(&bits[16]); 153 temp_dec = dht11_decode_byte(&bits[24]); 154 checksum = dht11_decode_byte(&bits[32]); 155 156 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) { 157 dev_dbg(dht11->dev, "invalid checksum\n"); 158 return -EIO; 159 } 160 161 dht11->timestamp = ktime_get_boot_ns(); 162 if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */ 163 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * 164 ((temp_int & 0x80) ? -100 : 100); 165 dht11->humidity = ((hum_int << 8) + hum_dec) * 100; 166 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ 167 dht11->temperature = temp_int * 1000; 168 dht11->humidity = hum_int * 1000; 169 } else { 170 dev_err(dht11->dev, 171 "Don't know how to decode data: %d %d %d %d\n", 172 hum_int, hum_dec, temp_int, temp_dec); 173 return -EIO; 174 } 175 176 return 0; 177 } 178 179 /* 180 * IRQ handler called on GPIO edges 181 */ 182 static irqreturn_t dht11_handle_irq(int irq, void *data) 183 { 184 struct iio_dev *iio = data; 185 struct dht11 *dht11 = iio_priv(iio); 186 187 /* TODO: Consider making the handler safe for IRQ sharing */ 188 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { 189 dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns(); 190 dht11->edges[dht11->num_edges++].value = 191 gpio_get_value(dht11->gpio); 192 193 if (dht11->num_edges >= DHT11_EDGES_PER_READ) 194 complete(&dht11->completion); 195 } 196 197 return IRQ_HANDLED; 198 } 199 200 static int dht11_read_raw(struct iio_dev *iio_dev, 201 const struct iio_chan_spec *chan, 202 int *val, int *val2, long m) 203 { 204 struct dht11 *dht11 = iio_priv(iio_dev); 205 int ret, timeres, offset; 206 207 mutex_lock(&dht11->lock); 208 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) { 209 timeres = ktime_get_resolution_ns(); 210 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres); 211 if (timeres > DHT11_MIN_TIMERES) { 212 dev_err(dht11->dev, "timeresolution %dns too low\n", 213 timeres); 214 /* In theory a better clock could become available 215 * at some point ... and there is no error code 216 * that really fits better. 217 */ 218 ret = -EAGAIN; 219 goto err; 220 } 221 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH) 222 dev_warn(dht11->dev, 223 "timeresolution: %dns - decoding ambiguous\n", 224 timeres); 225 226 reinit_completion(&dht11->completion); 227 228 dht11->num_edges = 0; 229 ret = gpio_direction_output(dht11->gpio, 0); 230 if (ret) 231 goto err; 232 usleep_range(DHT11_START_TRANSMISSION_MIN, 233 DHT11_START_TRANSMISSION_MAX); 234 ret = gpio_direction_input(dht11->gpio); 235 if (ret) 236 goto err; 237 238 ret = request_irq(dht11->irq, dht11_handle_irq, 239 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, 240 iio_dev->name, iio_dev); 241 if (ret) 242 goto err; 243 244 ret = wait_for_completion_killable_timeout(&dht11->completion, 245 HZ); 246 247 free_irq(dht11->irq, iio_dev); 248 249 #ifdef CONFIG_DYNAMIC_DEBUG 250 dht11_edges_print(dht11); 251 #endif 252 253 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { 254 dev_err(dht11->dev, "Only %d signal edges detected\n", 255 dht11->num_edges); 256 ret = -ETIMEDOUT; 257 } 258 if (ret < 0) 259 goto err; 260 261 offset = DHT11_EDGES_PREAMBLE + 262 dht11->num_edges - DHT11_EDGES_PER_READ; 263 for (; offset >= 0; --offset) { 264 ret = dht11_decode(dht11, offset); 265 if (!ret) 266 break; 267 } 268 269 if (ret) 270 goto err; 271 } 272 273 ret = IIO_VAL_INT; 274 if (chan->type == IIO_TEMP) 275 *val = dht11->temperature; 276 else if (chan->type == IIO_HUMIDITYRELATIVE) 277 *val = dht11->humidity; 278 else 279 ret = -EINVAL; 280 err: 281 dht11->num_edges = -1; 282 mutex_unlock(&dht11->lock); 283 return ret; 284 } 285 286 static const struct iio_info dht11_iio_info = { 287 .read_raw = dht11_read_raw, 288 }; 289 290 static const struct iio_chan_spec dht11_chan_spec[] = { 291 { .type = IIO_TEMP, 292 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, 293 { .type = IIO_HUMIDITYRELATIVE, 294 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } 295 }; 296 297 static const struct of_device_id dht11_dt_ids[] = { 298 { .compatible = "dht11", }, 299 { } 300 }; 301 MODULE_DEVICE_TABLE(of, dht11_dt_ids); 302 303 static int dht11_probe(struct platform_device *pdev) 304 { 305 struct device *dev = &pdev->dev; 306 struct device_node *node = dev->of_node; 307 struct dht11 *dht11; 308 struct iio_dev *iio; 309 int ret; 310 311 iio = devm_iio_device_alloc(dev, sizeof(*dht11)); 312 if (!iio) { 313 dev_err(dev, "Failed to allocate IIO device\n"); 314 return -ENOMEM; 315 } 316 317 dht11 = iio_priv(iio); 318 dht11->dev = dev; 319 320 ret = of_get_gpio(node, 0); 321 if (ret < 0) 322 return ret; 323 dht11->gpio = ret; 324 ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name); 325 if (ret) 326 return ret; 327 328 dht11->irq = gpio_to_irq(dht11->gpio); 329 if (dht11->irq < 0) { 330 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio); 331 return -EINVAL; 332 } 333 334 dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1; 335 dht11->num_edges = -1; 336 337 platform_set_drvdata(pdev, iio); 338 339 init_completion(&dht11->completion); 340 mutex_init(&dht11->lock); 341 iio->name = pdev->name; 342 iio->dev.parent = &pdev->dev; 343 iio->info = &dht11_iio_info; 344 iio->modes = INDIO_DIRECT_MODE; 345 iio->channels = dht11_chan_spec; 346 iio->num_channels = ARRAY_SIZE(dht11_chan_spec); 347 348 return devm_iio_device_register(dev, iio); 349 } 350 351 static struct platform_driver dht11_driver = { 352 .driver = { 353 .name = DRIVER_NAME, 354 .of_match_table = dht11_dt_ids, 355 }, 356 .probe = dht11_probe, 357 }; 358 359 module_platform_driver(dht11_driver); 360 361 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); 362 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); 363 MODULE_LICENSE("GPL v2"); 364