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/of.h> 15 #include <linux/of_device.h> 16 #include <linux/sysfs.h> 17 #include <linux/io.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 DRIVER_NAME "dht11" 31 32 #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ 33 34 #define DHT11_EDGES_PREAMBLE 2 35 #define DHT11_BITS_PER_READ 40 36 /* 37 * Note that when reading the sensor actually 84 edges are detected, but 38 * since the last edge is not significant, we only store 83: 39 */ 40 #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \ 41 DHT11_EDGES_PREAMBLE + 1) 42 43 /* 44 * Data transmission timing: 45 * Data bits are encoded as pulse length (high time) on the data line. 46 * 0-bit: 22-30uS -- typically 26uS (AM2302) 47 * 1-bit: 68-75uS -- typically 70uS (AM2302) 48 * The acutal timings also depend on the properties of the cable, with 49 * longer cables typically making pulses shorter. 50 * 51 * Our decoding depends on the time resolution of the system: 52 * timeres > 34uS ... don't know what a 1-tick pulse is 53 * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks) 54 * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is 55 * timeres < 23uS ... no problem 56 * 57 * Luckily clocks in the 33-44kHz range are quite uncommon, so we can 58 * support most systems if the threshold for decoding a pulse as 1-bit 59 * is chosen carefully. If somebody really wants to support clocks around 60 * 40kHz, where this driver is most unreliable, there are two options. 61 * a) select an implementation using busy loop polling on those systems 62 * b) use the checksum to do some probabilistic decoding 63 */ 64 #define DHT11_START_TRANSMISSION_MIN 18000 /* us */ 65 #define DHT11_START_TRANSMISSION_MAX 20000 /* us */ 66 #define DHT11_MIN_TIMERES 34000 /* ns */ 67 #define DHT11_THRESHOLD 49000 /* ns */ 68 #define DHT11_AMBIG_LOW 23000 /* ns */ 69 #define DHT11_AMBIG_HIGH 30000 /* ns */ 70 71 struct dht11 { 72 struct device *dev; 73 74 struct gpio_desc *gpiod; 75 int irq; 76 77 struct completion completion; 78 /* The iio sysfs interface doesn't prevent concurrent reads: */ 79 struct mutex lock; 80 81 s64 timestamp; 82 int temperature; 83 int humidity; 84 85 /* num_edges: -1 means "no transmission in progress" */ 86 int num_edges; 87 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; 88 }; 89 90 #ifdef CONFIG_DYNAMIC_DEBUG 91 /* 92 * dht11_edges_print: show the data as actually received by the 93 * driver. 94 */ 95 static void dht11_edges_print(struct dht11 *dht11) 96 { 97 int i; 98 99 dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges); 100 for (i = 1; i < dht11->num_edges; ++i) { 101 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i, 102 dht11->edges[i].ts - dht11->edges[i - 1].ts, 103 dht11->edges[i - 1].value ? "high" : "low"); 104 } 105 } 106 #endif /* CONFIG_DYNAMIC_DEBUG */ 107 108 static unsigned char dht11_decode_byte(char *bits) 109 { 110 unsigned char ret = 0; 111 int i; 112 113 for (i = 0; i < 8; ++i) { 114 ret <<= 1; 115 if (bits[i]) 116 ++ret; 117 } 118 119 return ret; 120 } 121 122 static int dht11_decode(struct dht11 *dht11, int offset) 123 { 124 int i, t; 125 char bits[DHT11_BITS_PER_READ]; 126 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; 127 128 for (i = 0; i < DHT11_BITS_PER_READ; ++i) { 129 t = dht11->edges[offset + 2 * i + 2].ts - 130 dht11->edges[offset + 2 * i + 1].ts; 131 if (!dht11->edges[offset + 2 * i + 1].value) { 132 dev_dbg(dht11->dev, 133 "lost synchronisation at edge %d\n", 134 offset + 2 * i + 1); 135 return -EIO; 136 } 137 bits[i] = t > DHT11_THRESHOLD; 138 } 139 140 hum_int = dht11_decode_byte(bits); 141 hum_dec = dht11_decode_byte(&bits[8]); 142 temp_int = dht11_decode_byte(&bits[16]); 143 temp_dec = dht11_decode_byte(&bits[24]); 144 checksum = dht11_decode_byte(&bits[32]); 145 146 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) { 147 dev_dbg(dht11->dev, "invalid checksum\n"); 148 return -EIO; 149 } 150 151 dht11->timestamp = ktime_get_boottime_ns(); 152 if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */ 153 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * 154 ((temp_int & 0x80) ? -100 : 100); 155 dht11->humidity = ((hum_int << 8) + hum_dec) * 100; 156 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ 157 dht11->temperature = temp_int * 1000; 158 dht11->humidity = hum_int * 1000; 159 } else { 160 dev_err(dht11->dev, 161 "Don't know how to decode data: %d %d %d %d\n", 162 hum_int, hum_dec, temp_int, temp_dec); 163 return -EIO; 164 } 165 166 return 0; 167 } 168 169 /* 170 * IRQ handler called on GPIO edges 171 */ 172 static irqreturn_t dht11_handle_irq(int irq, void *data) 173 { 174 struct iio_dev *iio = data; 175 struct dht11 *dht11 = iio_priv(iio); 176 177 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { 178 dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns(); 179 dht11->edges[dht11->num_edges++].value = 180 gpiod_get_value(dht11->gpiod); 181 182 if (dht11->num_edges >= DHT11_EDGES_PER_READ) 183 complete(&dht11->completion); 184 } 185 186 return IRQ_HANDLED; 187 } 188 189 static int dht11_read_raw(struct iio_dev *iio_dev, 190 const struct iio_chan_spec *chan, 191 int *val, int *val2, long m) 192 { 193 struct dht11 *dht11 = iio_priv(iio_dev); 194 int ret, timeres, offset; 195 196 mutex_lock(&dht11->lock); 197 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boottime_ns()) { 198 timeres = ktime_get_resolution_ns(); 199 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres); 200 if (timeres > DHT11_MIN_TIMERES) { 201 dev_err(dht11->dev, "timeresolution %dns too low\n", 202 timeres); 203 /* In theory a better clock could become available 204 * at some point ... and there is no error code 205 * that really fits better. 206 */ 207 ret = -EAGAIN; 208 goto err; 209 } 210 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH) 211 dev_warn(dht11->dev, 212 "timeresolution: %dns - decoding ambiguous\n", 213 timeres); 214 215 reinit_completion(&dht11->completion); 216 217 dht11->num_edges = 0; 218 ret = gpiod_direction_output(dht11->gpiod, 0); 219 if (ret) 220 goto err; 221 usleep_range(DHT11_START_TRANSMISSION_MIN, 222 DHT11_START_TRANSMISSION_MAX); 223 ret = gpiod_direction_input(dht11->gpiod); 224 if (ret) 225 goto err; 226 227 ret = request_irq(dht11->irq, dht11_handle_irq, 228 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, 229 iio_dev->name, iio_dev); 230 if (ret) 231 goto err; 232 233 ret = wait_for_completion_killable_timeout(&dht11->completion, 234 HZ); 235 236 free_irq(dht11->irq, iio_dev); 237 238 #ifdef CONFIG_DYNAMIC_DEBUG 239 dht11_edges_print(dht11); 240 #endif 241 242 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { 243 dev_err(dht11->dev, "Only %d signal edges detected\n", 244 dht11->num_edges); 245 ret = -ETIMEDOUT; 246 } 247 if (ret < 0) 248 goto err; 249 250 offset = DHT11_EDGES_PREAMBLE + 251 dht11->num_edges - DHT11_EDGES_PER_READ; 252 for (; offset >= 0; --offset) { 253 ret = dht11_decode(dht11, offset); 254 if (!ret) 255 break; 256 } 257 258 if (ret) 259 goto err; 260 } 261 262 ret = IIO_VAL_INT; 263 if (chan->type == IIO_TEMP) 264 *val = dht11->temperature; 265 else if (chan->type == IIO_HUMIDITYRELATIVE) 266 *val = dht11->humidity; 267 else 268 ret = -EINVAL; 269 err: 270 dht11->num_edges = -1; 271 mutex_unlock(&dht11->lock); 272 return ret; 273 } 274 275 static const struct iio_info dht11_iio_info = { 276 .read_raw = dht11_read_raw, 277 }; 278 279 static const struct iio_chan_spec dht11_chan_spec[] = { 280 { .type = IIO_TEMP, 281 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, 282 { .type = IIO_HUMIDITYRELATIVE, 283 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } 284 }; 285 286 static const struct of_device_id dht11_dt_ids[] = { 287 { .compatible = "dht11", }, 288 { } 289 }; 290 MODULE_DEVICE_TABLE(of, dht11_dt_ids); 291 292 static int dht11_probe(struct platform_device *pdev) 293 { 294 struct device *dev = &pdev->dev; 295 struct dht11 *dht11; 296 struct iio_dev *iio; 297 298 iio = devm_iio_device_alloc(dev, sizeof(*dht11)); 299 if (!iio) { 300 dev_err(dev, "Failed to allocate IIO device\n"); 301 return -ENOMEM; 302 } 303 304 dht11 = iio_priv(iio); 305 dht11->dev = dev; 306 dht11->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN); 307 if (IS_ERR(dht11->gpiod)) 308 return PTR_ERR(dht11->gpiod); 309 310 dht11->irq = gpiod_to_irq(dht11->gpiod); 311 if (dht11->irq < 0) { 312 dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod)); 313 return -EINVAL; 314 } 315 316 dht11->timestamp = ktime_get_boottime_ns() - DHT11_DATA_VALID_TIME - 1; 317 dht11->num_edges = -1; 318 319 platform_set_drvdata(pdev, iio); 320 321 init_completion(&dht11->completion); 322 mutex_init(&dht11->lock); 323 iio->name = pdev->name; 324 iio->dev.parent = &pdev->dev; 325 iio->info = &dht11_iio_info; 326 iio->modes = INDIO_DIRECT_MODE; 327 iio->channels = dht11_chan_spec; 328 iio->num_channels = ARRAY_SIZE(dht11_chan_spec); 329 330 return devm_iio_device_register(dev, iio); 331 } 332 333 static struct platform_driver dht11_driver = { 334 .driver = { 335 .name = DRIVER_NAME, 336 .of_match_table = dht11_dt_ids, 337 }, 338 .probe = dht11_probe, 339 }; 340 341 module_platform_driver(dht11_driver); 342 343 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); 344 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); 345 MODULE_LICENSE("GPL v2"); 346