1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * DHT11/DHT22 bit banging GPIO driver 4 * 5 * Copyright (c) Harald Geyer <harald@ccbib.org> 6 */ 7 8 #include <linux/err.h> 9 #include <linux/interrupt.h> 10 #include <linux/device.h> 11 #include <linux/kernel.h> 12 #include <linux/printk.h> 13 #include <linux/slab.h> 14 #include <linux/string_choices.h> 15 #include <linux/sysfs.h> 16 #include <linux/io.h> 17 #include <linux/mod_devicetable.h> 18 #include <linux/module.h> 19 #include <linux/platform_device.h> 20 #include <linux/wait.h> 21 #include <linux/bitops.h> 22 #include <linux/completion.h> 23 #include <linux/mutex.h> 24 #include <linux/delay.h> 25 #include <linux/gpio/consumer.h> 26 #include <linux/timekeeping.h> 27 28 #include <linux/iio/iio.h> 29 30 #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ 31 32 #define DHT11_EDGES_PREAMBLE 2 33 #define DHT11_BITS_PER_READ 40 34 /* 35 * Note that when reading the sensor actually 84 edges are detected, but 36 * since the last edge is not significant, we only store 83: 37 */ 38 #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \ 39 DHT11_EDGES_PREAMBLE + 1) 40 41 /* 42 * Data transmission timing: 43 * Data bits are encoded as pulse length (high time) on the data line. 44 * 0-bit: 22-30uS -- typically 26uS (AM2302) 45 * 1-bit: 68-75uS -- typically 70uS (AM2302) 46 * The acutal timings also depend on the properties of the cable, with 47 * longer cables typically making pulses shorter. 48 * 49 * Our decoding depends on the time resolution of the system: 50 * timeres > 34uS ... don't know what a 1-tick pulse is 51 * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks) 52 * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is 53 * timeres < 23uS ... no problem 54 * 55 * Luckily clocks in the 33-44kHz range are quite uncommon, so we can 56 * support most systems if the threshold for decoding a pulse as 1-bit 57 * is chosen carefully. If somebody really wants to support clocks around 58 * 40kHz, where this driver is most unreliable, there are two options. 59 * a) select an implementation using busy loop polling on those systems 60 * b) use the checksum to do some probabilistic decoding 61 */ 62 #define DHT11_START_TRANSMISSION_MIN 18000 /* us */ 63 #define DHT11_START_TRANSMISSION_MAX 20000 /* us */ 64 #define DHT11_MIN_TIMERES 34000 /* ns */ 65 #define DHT11_THRESHOLD 49000 /* ns */ 66 #define DHT11_AMBIG_LOW 23000 /* ns */ 67 #define DHT11_AMBIG_HIGH 30000 /* ns */ 68 69 struct dht11 { 70 struct device *dev; 71 72 struct gpio_desc *gpiod; 73 int irq; 74 75 struct completion completion; 76 /* The iio sysfs interface doesn't prevent concurrent reads: */ 77 struct mutex lock; 78 79 s64 timestamp; 80 int temperature; 81 int humidity; 82 83 /* num_edges: -1 means "no transmission in progress" */ 84 int num_edges; 85 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; 86 }; 87 88 #ifdef CONFIG_DYNAMIC_DEBUG 89 /* 90 * dht11_edges_print: show the data as actually received by the 91 * driver. 92 */ 93 static void dht11_edges_print(struct dht11 *dht11) 94 { 95 int i; 96 97 dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges); 98 for (i = 1; i < dht11->num_edges; ++i) { 99 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i, 100 dht11->edges[i].ts - dht11->edges[i - 1].ts, 101 str_high_low(dht11->edges[i - 1].value)); 102 } 103 } 104 #endif /* CONFIG_DYNAMIC_DEBUG */ 105 106 static unsigned char dht11_decode_byte(char *bits) 107 { 108 unsigned char ret = 0; 109 int i; 110 111 for (i = 0; i < 8; ++i) { 112 ret <<= 1; 113 if (bits[i]) 114 ++ret; 115 } 116 117 return ret; 118 } 119 120 static int dht11_decode(struct dht11 *dht11, int offset) 121 { 122 int i, t; 123 char bits[DHT11_BITS_PER_READ]; 124 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; 125 126 for (i = 0; i < DHT11_BITS_PER_READ; ++i) { 127 t = dht11->edges[offset + 2 * i + 2].ts - 128 dht11->edges[offset + 2 * i + 1].ts; 129 if (!dht11->edges[offset + 2 * i + 1].value) { 130 dev_dbg(dht11->dev, 131 "lost synchronisation at edge %d\n", 132 offset + 2 * i + 1); 133 return -EIO; 134 } 135 bits[i] = t > DHT11_THRESHOLD; 136 } 137 138 hum_int = dht11_decode_byte(bits); 139 hum_dec = dht11_decode_byte(&bits[8]); 140 temp_int = dht11_decode_byte(&bits[16]); 141 temp_dec = dht11_decode_byte(&bits[24]); 142 checksum = dht11_decode_byte(&bits[32]); 143 144 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) { 145 dev_dbg(dht11->dev, "invalid checksum\n"); 146 return -EIO; 147 } 148 149 dht11->timestamp = ktime_get_boottime_ns(); 150 if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */ 151 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * 152 ((temp_int & 0x80) ? -100 : 100); 153 dht11->humidity = ((hum_int << 8) + hum_dec) * 100; 154 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ 155 dht11->temperature = temp_int * 1000; 156 dht11->humidity = hum_int * 1000; 157 } else { 158 dev_err(dht11->dev, 159 "Don't know how to decode data: %d %d %d %d\n", 160 hum_int, hum_dec, temp_int, temp_dec); 161 return -EIO; 162 } 163 164 return 0; 165 } 166 167 /* 168 * IRQ handler called on GPIO edges 169 */ 170 static irqreturn_t dht11_handle_irq(int irq, void *data) 171 { 172 struct iio_dev *iio = data; 173 struct dht11 *dht11 = iio_priv(iio); 174 175 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { 176 dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns(); 177 dht11->edges[dht11->num_edges++].value = 178 gpiod_get_value(dht11->gpiod); 179 180 if (dht11->num_edges >= DHT11_EDGES_PER_READ) 181 complete(&dht11->completion); 182 } 183 184 return IRQ_HANDLED; 185 } 186 187 static int dht11_read_raw(struct iio_dev *iio_dev, 188 const struct iio_chan_spec *chan, 189 int *val, int *val2, long m) 190 { 191 struct dht11 *dht11 = iio_priv(iio_dev); 192 int ret, timeres, offset; 193 194 mutex_lock(&dht11->lock); 195 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boottime_ns()) { 196 timeres = ktime_get_resolution_ns(); 197 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres); 198 if (timeres > DHT11_MIN_TIMERES) { 199 dev_err(dht11->dev, "timeresolution %dns too low\n", 200 timeres); 201 /* In theory a better clock could become available 202 * at some point ... and there is no error code 203 * that really fits better. 204 */ 205 ret = -EAGAIN; 206 goto err; 207 } 208 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH) 209 dev_warn(dht11->dev, 210 "timeresolution: %dns - decoding ambiguous\n", 211 timeres); 212 213 reinit_completion(&dht11->completion); 214 215 dht11->num_edges = 0; 216 ret = gpiod_direction_output(dht11->gpiod, 0); 217 if (ret) 218 goto err; 219 usleep_range(DHT11_START_TRANSMISSION_MIN, 220 DHT11_START_TRANSMISSION_MAX); 221 ret = gpiod_direction_input(dht11->gpiod); 222 if (ret) 223 goto err; 224 225 ret = request_irq(dht11->irq, dht11_handle_irq, 226 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, 227 iio_dev->name, iio_dev); 228 if (ret) 229 goto err; 230 231 ret = wait_for_completion_killable_timeout(&dht11->completion, 232 HZ); 233 234 free_irq(dht11->irq, iio_dev); 235 236 #ifdef CONFIG_DYNAMIC_DEBUG 237 dht11_edges_print(dht11); 238 #endif 239 240 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { 241 dev_err(dht11->dev, "Only %d signal edges detected\n", 242 dht11->num_edges); 243 ret = -ETIMEDOUT; 244 } 245 if (ret < 0) 246 goto err; 247 248 offset = DHT11_EDGES_PREAMBLE + 249 dht11->num_edges - DHT11_EDGES_PER_READ; 250 for (; offset >= 0; --offset) { 251 ret = dht11_decode(dht11, offset); 252 if (!ret) 253 break; 254 } 255 256 if (ret) 257 goto err; 258 } 259 260 ret = IIO_VAL_INT; 261 if (chan->type == IIO_TEMP) 262 *val = dht11->temperature; 263 else if (chan->type == IIO_HUMIDITYRELATIVE) 264 *val = dht11->humidity; 265 else 266 ret = -EINVAL; 267 err: 268 dht11->num_edges = -1; 269 mutex_unlock(&dht11->lock); 270 return ret; 271 } 272 273 static const struct iio_info dht11_iio_info = { 274 .read_raw = dht11_read_raw, 275 }; 276 277 static const struct iio_chan_spec dht11_chan_spec[] = { 278 { .type = IIO_TEMP, 279 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, 280 { .type = IIO_HUMIDITYRELATIVE, 281 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } 282 }; 283 284 static const struct of_device_id dht11_dt_ids[] = { 285 { .compatible = "dht11", }, 286 { } 287 }; 288 MODULE_DEVICE_TABLE(of, dht11_dt_ids); 289 290 static int dht11_probe(struct platform_device *pdev) 291 { 292 struct device *dev = &pdev->dev; 293 struct dht11 *dht11; 294 struct iio_dev *iio; 295 296 iio = devm_iio_device_alloc(dev, sizeof(*dht11)); 297 if (!iio) { 298 dev_err(dev, "Failed to allocate IIO device\n"); 299 return -ENOMEM; 300 } 301 302 dht11 = iio_priv(iio); 303 dht11->dev = dev; 304 dht11->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN); 305 if (IS_ERR(dht11->gpiod)) 306 return PTR_ERR(dht11->gpiod); 307 308 dht11->irq = gpiod_to_irq(dht11->gpiod); 309 if (dht11->irq < 0) { 310 dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod)); 311 return -EINVAL; 312 } 313 314 dht11->timestamp = ktime_get_boottime_ns() - DHT11_DATA_VALID_TIME - 1; 315 dht11->num_edges = -1; 316 317 platform_set_drvdata(pdev, iio); 318 319 init_completion(&dht11->completion); 320 mutex_init(&dht11->lock); 321 iio->name = pdev->name; 322 iio->info = &dht11_iio_info; 323 iio->modes = INDIO_DIRECT_MODE; 324 iio->channels = dht11_chan_spec; 325 iio->num_channels = ARRAY_SIZE(dht11_chan_spec); 326 327 return devm_iio_device_register(dev, iio); 328 } 329 330 static struct platform_driver dht11_driver = { 331 .driver = { 332 .name = "dht11", 333 .of_match_table = dht11_dt_ids, 334 }, 335 .probe = dht11_probe, 336 }; 337 338 module_platform_driver(dht11_driver); 339 340 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); 341 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); 342 MODULE_LICENSE("GPL v2"); 343