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/sysfs.h> 15 #include <linux/io.h> 16 #include <linux/mod_devicetable.h> 17 #include <linux/module.h> 18 #include <linux/platform_device.h> 19 #include <linux/wait.h> 20 #include <linux/bitops.h> 21 #include <linux/completion.h> 22 #include <linux/mutex.h> 23 #include <linux/delay.h> 24 #include <linux/gpio/consumer.h> 25 #include <linux/timekeeping.h> 26 27 #include <linux/iio/iio.h> 28 29 #define DRIVER_NAME "dht11" 30 31 #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ 32 33 #define DHT11_EDGES_PREAMBLE 2 34 #define DHT11_BITS_PER_READ 40 35 /* 36 * Note that when reading the sensor actually 84 edges are detected, but 37 * since the last edge is not significant, we only store 83: 38 */ 39 #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \ 40 DHT11_EDGES_PREAMBLE + 1) 41 42 /* 43 * Data transmission timing: 44 * Data bits are encoded as pulse length (high time) on the data line. 45 * 0-bit: 22-30uS -- typically 26uS (AM2302) 46 * 1-bit: 68-75uS -- typically 70uS (AM2302) 47 * The acutal timings also depend on the properties of the cable, with 48 * longer cables typically making pulses shorter. 49 * 50 * Our decoding depends on the time resolution of the system: 51 * timeres > 34uS ... don't know what a 1-tick pulse is 52 * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks) 53 * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is 54 * timeres < 23uS ... no problem 55 * 56 * Luckily clocks in the 33-44kHz range are quite uncommon, so we can 57 * support most systems if the threshold for decoding a pulse as 1-bit 58 * is chosen carefully. If somebody really wants to support clocks around 59 * 40kHz, where this driver is most unreliable, there are two options. 60 * a) select an implementation using busy loop polling on those systems 61 * b) use the checksum to do some probabilistic decoding 62 */ 63 #define DHT11_START_TRANSMISSION_MIN 18000 /* us */ 64 #define DHT11_START_TRANSMISSION_MAX 20000 /* us */ 65 #define DHT11_MIN_TIMERES 34000 /* ns */ 66 #define DHT11_THRESHOLD 49000 /* ns */ 67 #define DHT11_AMBIG_LOW 23000 /* ns */ 68 #define DHT11_AMBIG_HIGH 30000 /* ns */ 69 70 struct dht11 { 71 struct device *dev; 72 73 struct gpio_desc *gpiod; 74 int irq; 75 76 struct completion completion; 77 /* The iio sysfs interface doesn't prevent concurrent reads: */ 78 struct mutex lock; 79 80 s64 timestamp; 81 int temperature; 82 int humidity; 83 84 /* num_edges: -1 means "no transmission in progress" */ 85 int num_edges; 86 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; 87 }; 88 89 #ifdef CONFIG_DYNAMIC_DEBUG 90 /* 91 * dht11_edges_print: show the data as actually received by the 92 * driver. 93 */ 94 static void dht11_edges_print(struct dht11 *dht11) 95 { 96 int i; 97 98 dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges); 99 for (i = 1; i < dht11->num_edges; ++i) { 100 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i, 101 dht11->edges[i].ts - dht11->edges[i - 1].ts, 102 dht11->edges[i - 1].value ? "high" : "low"); 103 } 104 } 105 #endif /* CONFIG_DYNAMIC_DEBUG */ 106 107 static unsigned char dht11_decode_byte(char *bits) 108 { 109 unsigned char ret = 0; 110 int i; 111 112 for (i = 0; i < 8; ++i) { 113 ret <<= 1; 114 if (bits[i]) 115 ++ret; 116 } 117 118 return ret; 119 } 120 121 static int dht11_decode(struct dht11 *dht11, int offset) 122 { 123 int i, t; 124 char bits[DHT11_BITS_PER_READ]; 125 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; 126 127 for (i = 0; i < DHT11_BITS_PER_READ; ++i) { 128 t = dht11->edges[offset + 2 * i + 2].ts - 129 dht11->edges[offset + 2 * i + 1].ts; 130 if (!dht11->edges[offset + 2 * i + 1].value) { 131 dev_dbg(dht11->dev, 132 "lost synchronisation at edge %d\n", 133 offset + 2 * i + 1); 134 return -EIO; 135 } 136 bits[i] = t > DHT11_THRESHOLD; 137 } 138 139 hum_int = dht11_decode_byte(bits); 140 hum_dec = dht11_decode_byte(&bits[8]); 141 temp_int = dht11_decode_byte(&bits[16]); 142 temp_dec = dht11_decode_byte(&bits[24]); 143 checksum = dht11_decode_byte(&bits[32]); 144 145 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) { 146 dev_dbg(dht11->dev, "invalid checksum\n"); 147 return -EIO; 148 } 149 150 dht11->timestamp = ktime_get_boottime_ns(); 151 if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */ 152 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * 153 ((temp_int & 0x80) ? -100 : 100); 154 dht11->humidity = ((hum_int << 8) + hum_dec) * 100; 155 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ 156 dht11->temperature = temp_int * 1000; 157 dht11->humidity = hum_int * 1000; 158 } else { 159 dev_err(dht11->dev, 160 "Don't know how to decode data: %d %d %d %d\n", 161 hum_int, hum_dec, temp_int, temp_dec); 162 return -EIO; 163 } 164 165 return 0; 166 } 167 168 /* 169 * IRQ handler called on GPIO edges 170 */ 171 static irqreturn_t dht11_handle_irq(int irq, void *data) 172 { 173 struct iio_dev *iio = data; 174 struct dht11 *dht11 = iio_priv(iio); 175 176 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { 177 dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns(); 178 dht11->edges[dht11->num_edges++].value = 179 gpiod_get_value(dht11->gpiod); 180 181 if (dht11->num_edges >= DHT11_EDGES_PER_READ) 182 complete(&dht11->completion); 183 } 184 185 return IRQ_HANDLED; 186 } 187 188 static int dht11_read_raw(struct iio_dev *iio_dev, 189 const struct iio_chan_spec *chan, 190 int *val, int *val2, long m) 191 { 192 struct dht11 *dht11 = iio_priv(iio_dev); 193 int ret, timeres, offset; 194 195 mutex_lock(&dht11->lock); 196 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boottime_ns()) { 197 timeres = ktime_get_resolution_ns(); 198 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres); 199 if (timeres > DHT11_MIN_TIMERES) { 200 dev_err(dht11->dev, "timeresolution %dns too low\n", 201 timeres); 202 /* In theory a better clock could become available 203 * at some point ... and there is no error code 204 * that really fits better. 205 */ 206 ret = -EAGAIN; 207 goto err; 208 } 209 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH) 210 dev_warn(dht11->dev, 211 "timeresolution: %dns - decoding ambiguous\n", 212 timeres); 213 214 reinit_completion(&dht11->completion); 215 216 dht11->num_edges = 0; 217 ret = gpiod_direction_output(dht11->gpiod, 0); 218 if (ret) 219 goto err; 220 usleep_range(DHT11_START_TRANSMISSION_MIN, 221 DHT11_START_TRANSMISSION_MAX); 222 ret = gpiod_direction_input(dht11->gpiod); 223 if (ret) 224 goto err; 225 226 ret = request_irq(dht11->irq, dht11_handle_irq, 227 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, 228 iio_dev->name, iio_dev); 229 if (ret) 230 goto err; 231 232 ret = wait_for_completion_killable_timeout(&dht11->completion, 233 HZ); 234 235 free_irq(dht11->irq, iio_dev); 236 237 #ifdef CONFIG_DYNAMIC_DEBUG 238 dht11_edges_print(dht11); 239 #endif 240 241 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { 242 dev_err(dht11->dev, "Only %d signal edges detected\n", 243 dht11->num_edges); 244 ret = -ETIMEDOUT; 245 } 246 if (ret < 0) 247 goto err; 248 249 offset = DHT11_EDGES_PREAMBLE + 250 dht11->num_edges - DHT11_EDGES_PER_READ; 251 for (; offset >= 0; --offset) { 252 ret = dht11_decode(dht11, offset); 253 if (!ret) 254 break; 255 } 256 257 if (ret) 258 goto err; 259 } 260 261 ret = IIO_VAL_INT; 262 if (chan->type == IIO_TEMP) 263 *val = dht11->temperature; 264 else if (chan->type == IIO_HUMIDITYRELATIVE) 265 *val = dht11->humidity; 266 else 267 ret = -EINVAL; 268 err: 269 dht11->num_edges = -1; 270 mutex_unlock(&dht11->lock); 271 return ret; 272 } 273 274 static const struct iio_info dht11_iio_info = { 275 .read_raw = dht11_read_raw, 276 }; 277 278 static const struct iio_chan_spec dht11_chan_spec[] = { 279 { .type = IIO_TEMP, 280 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, 281 { .type = IIO_HUMIDITYRELATIVE, 282 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } 283 }; 284 285 static const struct of_device_id dht11_dt_ids[] = { 286 { .compatible = "dht11", }, 287 { } 288 }; 289 MODULE_DEVICE_TABLE(of, dht11_dt_ids); 290 291 static int dht11_probe(struct platform_device *pdev) 292 { 293 struct device *dev = &pdev->dev; 294 struct dht11 *dht11; 295 struct iio_dev *iio; 296 297 iio = devm_iio_device_alloc(dev, sizeof(*dht11)); 298 if (!iio) { 299 dev_err(dev, "Failed to allocate IIO device\n"); 300 return -ENOMEM; 301 } 302 303 dht11 = iio_priv(iio); 304 dht11->dev = dev; 305 dht11->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN); 306 if (IS_ERR(dht11->gpiod)) 307 return PTR_ERR(dht11->gpiod); 308 309 dht11->irq = gpiod_to_irq(dht11->gpiod); 310 if (dht11->irq < 0) { 311 dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod)); 312 return -EINVAL; 313 } 314 315 dht11->timestamp = ktime_get_boottime_ns() - DHT11_DATA_VALID_TIME - 1; 316 dht11->num_edges = -1; 317 318 platform_set_drvdata(pdev, iio); 319 320 init_completion(&dht11->completion); 321 mutex_init(&dht11->lock); 322 iio->name = pdev->name; 323 iio->info = &dht11_iio_info; 324 iio->modes = INDIO_DIRECT_MODE; 325 iio->channels = dht11_chan_spec; 326 iio->num_channels = ARRAY_SIZE(dht11_chan_spec); 327 328 return devm_iio_device_register(dev, iio); 329 } 330 331 static struct platform_driver dht11_driver = { 332 .driver = { 333 .name = DRIVER_NAME, 334 .of_match_table = dht11_dt_ids, 335 }, 336 .probe = dht11_probe, 337 }; 338 339 module_platform_driver(dht11_driver); 340 341 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); 342 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); 343 MODULE_LICENSE("GPL v2"); 344