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 /* TODO: Consider making the handler safe for IRQ sharing */ 178 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { 179 dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns(); 180 dht11->edges[dht11->num_edges++].value = 181 gpiod_get_value(dht11->gpiod); 182 183 if (dht11->num_edges >= DHT11_EDGES_PER_READ) 184 complete(&dht11->completion); 185 } 186 187 return IRQ_HANDLED; 188 } 189 190 static int dht11_read_raw(struct iio_dev *iio_dev, 191 const struct iio_chan_spec *chan, 192 int *val, int *val2, long m) 193 { 194 struct dht11 *dht11 = iio_priv(iio_dev); 195 int ret, timeres, offset; 196 197 mutex_lock(&dht11->lock); 198 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boottime_ns()) { 199 timeres = ktime_get_resolution_ns(); 200 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres); 201 if (timeres > DHT11_MIN_TIMERES) { 202 dev_err(dht11->dev, "timeresolution %dns too low\n", 203 timeres); 204 /* In theory a better clock could become available 205 * at some point ... and there is no error code 206 * that really fits better. 207 */ 208 ret = -EAGAIN; 209 goto err; 210 } 211 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH) 212 dev_warn(dht11->dev, 213 "timeresolution: %dns - decoding ambiguous\n", 214 timeres); 215 216 reinit_completion(&dht11->completion); 217 218 dht11->num_edges = 0; 219 ret = gpiod_direction_output(dht11->gpiod, 0); 220 if (ret) 221 goto err; 222 usleep_range(DHT11_START_TRANSMISSION_MIN, 223 DHT11_START_TRANSMISSION_MAX); 224 ret = gpiod_direction_input(dht11->gpiod); 225 if (ret) 226 goto err; 227 228 ret = request_irq(dht11->irq, dht11_handle_irq, 229 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, 230 iio_dev->name, iio_dev); 231 if (ret) 232 goto err; 233 234 ret = wait_for_completion_killable_timeout(&dht11->completion, 235 HZ); 236 237 free_irq(dht11->irq, iio_dev); 238 239 #ifdef CONFIG_DYNAMIC_DEBUG 240 dht11_edges_print(dht11); 241 #endif 242 243 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { 244 dev_err(dht11->dev, "Only %d signal edges detected\n", 245 dht11->num_edges); 246 ret = -ETIMEDOUT; 247 } 248 if (ret < 0) 249 goto err; 250 251 offset = DHT11_EDGES_PREAMBLE + 252 dht11->num_edges - DHT11_EDGES_PER_READ; 253 for (; offset >= 0; --offset) { 254 ret = dht11_decode(dht11, offset); 255 if (!ret) 256 break; 257 } 258 259 if (ret) 260 goto err; 261 } 262 263 ret = IIO_VAL_INT; 264 if (chan->type == IIO_TEMP) 265 *val = dht11->temperature; 266 else if (chan->type == IIO_HUMIDITYRELATIVE) 267 *val = dht11->humidity; 268 else 269 ret = -EINVAL; 270 err: 271 dht11->num_edges = -1; 272 mutex_unlock(&dht11->lock); 273 return ret; 274 } 275 276 static const struct iio_info dht11_iio_info = { 277 .read_raw = dht11_read_raw, 278 }; 279 280 static const struct iio_chan_spec dht11_chan_spec[] = { 281 { .type = IIO_TEMP, 282 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, 283 { .type = IIO_HUMIDITYRELATIVE, 284 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } 285 }; 286 287 static const struct of_device_id dht11_dt_ids[] = { 288 { .compatible = "dht11", }, 289 { } 290 }; 291 MODULE_DEVICE_TABLE(of, dht11_dt_ids); 292 293 static int dht11_probe(struct platform_device *pdev) 294 { 295 struct device *dev = &pdev->dev; 296 struct dht11 *dht11; 297 struct iio_dev *iio; 298 299 iio = devm_iio_device_alloc(dev, sizeof(*dht11)); 300 if (!iio) { 301 dev_err(dev, "Failed to allocate IIO device\n"); 302 return -ENOMEM; 303 } 304 305 dht11 = iio_priv(iio); 306 dht11->dev = dev; 307 dht11->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN); 308 if (IS_ERR(dht11->gpiod)) 309 return PTR_ERR(dht11->gpiod); 310 311 dht11->irq = gpiod_to_irq(dht11->gpiod); 312 if (dht11->irq < 0) { 313 dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod)); 314 return -EINVAL; 315 } 316 317 dht11->timestamp = ktime_get_boottime_ns() - DHT11_DATA_VALID_TIME - 1; 318 dht11->num_edges = -1; 319 320 platform_set_drvdata(pdev, iio); 321 322 init_completion(&dht11->completion); 323 mutex_init(&dht11->lock); 324 iio->name = pdev->name; 325 iio->dev.parent = &pdev->dev; 326 iio->info = &dht11_iio_info; 327 iio->modes = INDIO_DIRECT_MODE; 328 iio->channels = dht11_chan_spec; 329 iio->num_channels = ARRAY_SIZE(dht11_chan_spec); 330 331 return devm_iio_device_register(dev, iio); 332 } 333 334 static struct platform_driver dht11_driver = { 335 .driver = { 336 .name = DRIVER_NAME, 337 .of_match_table = dht11_dt_ids, 338 }, 339 .probe = dht11_probe, 340 }; 341 342 module_platform_driver(dht11_driver); 343 344 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); 345 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); 346 MODULE_LICENSE("GPL v2"); 347