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.h> 26 #include <linux/of_gpio.h> 27 #include <linux/timekeeping.h> 28 29 #include <linux/iio/iio.h> 30 31 #define DRIVER_NAME "dht11" 32 33 #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ 34 35 #define DHT11_EDGES_PREAMBLE 2 36 #define DHT11_BITS_PER_READ 40 37 /* 38 * Note that when reading the sensor actually 84 edges are detected, but 39 * since the last edge is not significant, we only store 83: 40 */ 41 #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \ 42 DHT11_EDGES_PREAMBLE + 1) 43 44 /* 45 * Data transmission timing: 46 * Data bits are encoded as pulse length (high time) on the data line. 47 * 0-bit: 22-30uS -- typically 26uS (AM2302) 48 * 1-bit: 68-75uS -- typically 70uS (AM2302) 49 * The acutal timings also depend on the properties of the cable, with 50 * longer cables typically making pulses shorter. 51 * 52 * Our decoding depends on the time resolution of the system: 53 * timeres > 34uS ... don't know what a 1-tick pulse is 54 * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks) 55 * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is 56 * timeres < 23uS ... no problem 57 * 58 * Luckily clocks in the 33-44kHz range are quite uncommon, so we can 59 * support most systems if the threshold for decoding a pulse as 1-bit 60 * is chosen carefully. If somebody really wants to support clocks around 61 * 40kHz, where this driver is most unreliable, there are two options. 62 * a) select an implementation using busy loop polling on those systems 63 * b) use the checksum to do some probabilistic decoding 64 */ 65 #define DHT11_START_TRANSMISSION_MIN 18000 /* us */ 66 #define DHT11_START_TRANSMISSION_MAX 20000 /* us */ 67 #define DHT11_MIN_TIMERES 34000 /* ns */ 68 #define DHT11_THRESHOLD 49000 /* ns */ 69 #define DHT11_AMBIG_LOW 23000 /* ns */ 70 #define DHT11_AMBIG_HIGH 30000 /* ns */ 71 72 struct dht11 { 73 struct device *dev; 74 75 int gpio; 76 int irq; 77 78 struct completion completion; 79 /* The iio sysfs interface doesn't prevent concurrent reads: */ 80 struct mutex lock; 81 82 s64 timestamp; 83 int temperature; 84 int humidity; 85 86 /* num_edges: -1 means "no transmission in progress" */ 87 int num_edges; 88 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; 89 }; 90 91 #ifdef CONFIG_DYNAMIC_DEBUG 92 /* 93 * dht11_edges_print: show the data as actually received by the 94 * driver. 95 */ 96 static void dht11_edges_print(struct dht11 *dht11) 97 { 98 int i; 99 100 dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges); 101 for (i = 1; i < dht11->num_edges; ++i) { 102 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i, 103 dht11->edges[i].ts - dht11->edges[i - 1].ts, 104 dht11->edges[i - 1].value ? "high" : "low"); 105 } 106 } 107 #endif /* CONFIG_DYNAMIC_DEBUG */ 108 109 static unsigned char dht11_decode_byte(char *bits) 110 { 111 unsigned char ret = 0; 112 int i; 113 114 for (i = 0; i < 8; ++i) { 115 ret <<= 1; 116 if (bits[i]) 117 ++ret; 118 } 119 120 return ret; 121 } 122 123 static int dht11_decode(struct dht11 *dht11, int offset) 124 { 125 int i, t; 126 char bits[DHT11_BITS_PER_READ]; 127 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; 128 129 for (i = 0; i < DHT11_BITS_PER_READ; ++i) { 130 t = dht11->edges[offset + 2 * i + 2].ts - 131 dht11->edges[offset + 2 * i + 1].ts; 132 if (!dht11->edges[offset + 2 * i + 1].value) { 133 dev_dbg(dht11->dev, 134 "lost synchronisation at edge %d\n", 135 offset + 2 * i + 1); 136 return -EIO; 137 } 138 bits[i] = t > DHT11_THRESHOLD; 139 } 140 141 hum_int = dht11_decode_byte(bits); 142 hum_dec = dht11_decode_byte(&bits[8]); 143 temp_int = dht11_decode_byte(&bits[16]); 144 temp_dec = dht11_decode_byte(&bits[24]); 145 checksum = dht11_decode_byte(&bits[32]); 146 147 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) { 148 dev_dbg(dht11->dev, "invalid checksum\n"); 149 return -EIO; 150 } 151 152 dht11->timestamp = ktime_get_boot_ns(); 153 if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */ 154 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * 155 ((temp_int & 0x80) ? -100 : 100); 156 dht11->humidity = ((hum_int << 8) + hum_dec) * 100; 157 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ 158 dht11->temperature = temp_int * 1000; 159 dht11->humidity = hum_int * 1000; 160 } else { 161 dev_err(dht11->dev, 162 "Don't know how to decode data: %d %d %d %d\n", 163 hum_int, hum_dec, temp_int, temp_dec); 164 return -EIO; 165 } 166 167 return 0; 168 } 169 170 /* 171 * IRQ handler called on GPIO edges 172 */ 173 static irqreturn_t dht11_handle_irq(int irq, void *data) 174 { 175 struct iio_dev *iio = data; 176 struct dht11 *dht11 = iio_priv(iio); 177 178 /* TODO: Consider making the handler safe for IRQ sharing */ 179 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { 180 dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns(); 181 dht11->edges[dht11->num_edges++].value = 182 gpio_get_value(dht11->gpio); 183 184 if (dht11->num_edges >= DHT11_EDGES_PER_READ) 185 complete(&dht11->completion); 186 } 187 188 return IRQ_HANDLED; 189 } 190 191 static int dht11_read_raw(struct iio_dev *iio_dev, 192 const struct iio_chan_spec *chan, 193 int *val, int *val2, long m) 194 { 195 struct dht11 *dht11 = iio_priv(iio_dev); 196 int ret, timeres, offset; 197 198 mutex_lock(&dht11->lock); 199 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) { 200 timeres = ktime_get_resolution_ns(); 201 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres); 202 if (timeres > DHT11_MIN_TIMERES) { 203 dev_err(dht11->dev, "timeresolution %dns too low\n", 204 timeres); 205 /* In theory a better clock could become available 206 * at some point ... and there is no error code 207 * that really fits better. 208 */ 209 ret = -EAGAIN; 210 goto err; 211 } 212 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH) 213 dev_warn(dht11->dev, 214 "timeresolution: %dns - decoding ambiguous\n", 215 timeres); 216 217 reinit_completion(&dht11->completion); 218 219 dht11->num_edges = 0; 220 ret = gpio_direction_output(dht11->gpio, 0); 221 if (ret) 222 goto err; 223 usleep_range(DHT11_START_TRANSMISSION_MIN, 224 DHT11_START_TRANSMISSION_MAX); 225 ret = gpio_direction_input(dht11->gpio); 226 if (ret) 227 goto err; 228 229 ret = request_irq(dht11->irq, dht11_handle_irq, 230 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, 231 iio_dev->name, iio_dev); 232 if (ret) 233 goto err; 234 235 ret = wait_for_completion_killable_timeout(&dht11->completion, 236 HZ); 237 238 free_irq(dht11->irq, iio_dev); 239 240 #ifdef CONFIG_DYNAMIC_DEBUG 241 dht11_edges_print(dht11); 242 #endif 243 244 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { 245 dev_err(dht11->dev, "Only %d signal edges detected\n", 246 dht11->num_edges); 247 ret = -ETIMEDOUT; 248 } 249 if (ret < 0) 250 goto err; 251 252 offset = DHT11_EDGES_PREAMBLE + 253 dht11->num_edges - DHT11_EDGES_PER_READ; 254 for (; offset >= 0; --offset) { 255 ret = dht11_decode(dht11, offset); 256 if (!ret) 257 break; 258 } 259 260 if (ret) 261 goto err; 262 } 263 264 ret = IIO_VAL_INT; 265 if (chan->type == IIO_TEMP) 266 *val = dht11->temperature; 267 else if (chan->type == IIO_HUMIDITYRELATIVE) 268 *val = dht11->humidity; 269 else 270 ret = -EINVAL; 271 err: 272 dht11->num_edges = -1; 273 mutex_unlock(&dht11->lock); 274 return ret; 275 } 276 277 static const struct iio_info dht11_iio_info = { 278 .read_raw = dht11_read_raw, 279 }; 280 281 static const struct iio_chan_spec dht11_chan_spec[] = { 282 { .type = IIO_TEMP, 283 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, 284 { .type = IIO_HUMIDITYRELATIVE, 285 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } 286 }; 287 288 static const struct of_device_id dht11_dt_ids[] = { 289 { .compatible = "dht11", }, 290 { } 291 }; 292 MODULE_DEVICE_TABLE(of, dht11_dt_ids); 293 294 static int dht11_probe(struct platform_device *pdev) 295 { 296 struct device *dev = &pdev->dev; 297 struct device_node *node = dev->of_node; 298 struct dht11 *dht11; 299 struct iio_dev *iio; 300 int ret; 301 302 iio = devm_iio_device_alloc(dev, sizeof(*dht11)); 303 if (!iio) { 304 dev_err(dev, "Failed to allocate IIO device\n"); 305 return -ENOMEM; 306 } 307 308 dht11 = iio_priv(iio); 309 dht11->dev = dev; 310 311 ret = of_get_gpio(node, 0); 312 if (ret < 0) 313 return ret; 314 dht11->gpio = ret; 315 ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name); 316 if (ret) 317 return ret; 318 319 dht11->irq = gpio_to_irq(dht11->gpio); 320 if (dht11->irq < 0) { 321 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio); 322 return -EINVAL; 323 } 324 325 dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1; 326 dht11->num_edges = -1; 327 328 platform_set_drvdata(pdev, iio); 329 330 init_completion(&dht11->completion); 331 mutex_init(&dht11->lock); 332 iio->name = pdev->name; 333 iio->dev.parent = &pdev->dev; 334 iio->info = &dht11_iio_info; 335 iio->modes = INDIO_DIRECT_MODE; 336 iio->channels = dht11_chan_spec; 337 iio->num_channels = ARRAY_SIZE(dht11_chan_spec); 338 339 return devm_iio_device_register(dev, iio); 340 } 341 342 static struct platform_driver dht11_driver = { 343 .driver = { 344 .name = DRIVER_NAME, 345 .of_match_table = dht11_dt_ids, 346 }, 347 .probe = dht11_probe, 348 }; 349 350 module_platform_driver(dht11_driver); 351 352 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); 353 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); 354 MODULE_LICENSE("GPL v2"); 355