1 /* 2 * DHT11/DHT22 bit banging GPIO driver 3 * 4 * Copyright (c) Harald Geyer <harald@ccbib.org> 5 * 6 * This program is free software; you can redistribute it and/or modify 7 * it under the terms of the GNU General Public License as published by 8 * the Free Software Foundation; either version 2 of the License, or 9 * (at your option) any later version. 10 * 11 * This program is distributed in the hope that it will be useful, 12 * but WITHOUT ANY WARRANTY; without even the implied warranty of 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 * GNU General Public License for more details. 15 */ 16 17 #include <linux/err.h> 18 #include <linux/interrupt.h> 19 #include <linux/device.h> 20 #include <linux/kernel.h> 21 #include <linux/printk.h> 22 #include <linux/slab.h> 23 #include <linux/of.h> 24 #include <linux/of_device.h> 25 #include <linux/sysfs.h> 26 #include <linux/io.h> 27 #include <linux/module.h> 28 #include <linux/platform_device.h> 29 #include <linux/wait.h> 30 #include <linux/bitops.h> 31 #include <linux/completion.h> 32 #include <linux/mutex.h> 33 #include <linux/delay.h> 34 #include <linux/gpio.h> 35 #include <linux/of_gpio.h> 36 37 #include <linux/iio/iio.h> 38 39 #define DRIVER_NAME "dht11" 40 41 #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ 42 43 #define DHT11_EDGES_PREAMBLE 2 44 #define DHT11_BITS_PER_READ 40 45 /* 46 * Note that when reading the sensor actually 84 edges are detected, but 47 * since the last edge is not significant, we only store 83: 48 */ 49 #define DHT11_EDGES_PER_READ (2*DHT11_BITS_PER_READ + DHT11_EDGES_PREAMBLE + 1) 50 51 /* Data transmission timing (nano seconds) */ 52 #define DHT11_START_TRANSMISSION 18 /* ms */ 53 #define DHT11_SENSOR_RESPONSE 80000 54 #define DHT11_START_BIT 50000 55 #define DHT11_DATA_BIT_LOW 27000 56 #define DHT11_DATA_BIT_HIGH 70000 57 58 struct dht11 { 59 struct device *dev; 60 61 int gpio; 62 int irq; 63 64 struct completion completion; 65 struct mutex lock; 66 67 s64 timestamp; 68 int temperature; 69 int humidity; 70 71 /* num_edges: -1 means "no transmission in progress" */ 72 int num_edges; 73 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; 74 }; 75 76 static unsigned char dht11_decode_byte(int *timing, int threshold) 77 { 78 unsigned char ret = 0; 79 int i; 80 81 for (i = 0; i < 8; ++i) { 82 ret <<= 1; 83 if (timing[i] >= threshold) 84 ++ret; 85 } 86 87 return ret; 88 } 89 90 static int dht11_decode(struct dht11 *dht11, int offset) 91 { 92 int i, t, timing[DHT11_BITS_PER_READ], threshold, 93 timeres = DHT11_SENSOR_RESPONSE; 94 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; 95 96 /* Calculate timestamp resolution */ 97 for (i = 1; i < dht11->num_edges; ++i) { 98 t = dht11->edges[i].ts - dht11->edges[i-1].ts; 99 if (t > 0 && t < timeres) 100 timeres = t; 101 } 102 if (2*timeres > DHT11_DATA_BIT_HIGH) { 103 pr_err("dht11: timeresolution %d too bad for decoding\n", 104 timeres); 105 return -EIO; 106 } 107 threshold = DHT11_DATA_BIT_HIGH / timeres; 108 if (DHT11_DATA_BIT_LOW/timeres + 1 >= threshold) 109 pr_err("dht11: WARNING: decoding ambiguous\n"); 110 111 /* scale down with timeres and check validity */ 112 for (i = 0; i < DHT11_BITS_PER_READ; ++i) { 113 t = dht11->edges[offset + 2*i + 2].ts - 114 dht11->edges[offset + 2*i + 1].ts; 115 if (!dht11->edges[offset + 2*i + 1].value) 116 return -EIO; /* lost synchronisation */ 117 timing[i] = t / timeres; 118 } 119 120 hum_int = dht11_decode_byte(timing, threshold); 121 hum_dec = dht11_decode_byte(&timing[8], threshold); 122 temp_int = dht11_decode_byte(&timing[16], threshold); 123 temp_dec = dht11_decode_byte(&timing[24], threshold); 124 checksum = dht11_decode_byte(&timing[32], threshold); 125 126 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) 127 return -EIO; 128 129 dht11->timestamp = iio_get_time_ns(); 130 if (hum_int < 20) { /* DHT22 */ 131 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * 132 ((temp_int & 0x80) ? -100 : 100); 133 dht11->humidity = ((hum_int << 8) + hum_dec) * 100; 134 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ 135 dht11->temperature = temp_int * 1000; 136 dht11->humidity = hum_int * 1000; 137 } else { 138 dev_err(dht11->dev, 139 "Don't know how to decode data: %d %d %d %d\n", 140 hum_int, hum_dec, temp_int, temp_dec); 141 return -EIO; 142 } 143 144 return 0; 145 } 146 147 /* 148 * IRQ handler called on GPIO edges 149 */ 150 static irqreturn_t dht11_handle_irq(int irq, void *data) 151 { 152 struct iio_dev *iio = data; 153 struct dht11 *dht11 = iio_priv(iio); 154 155 /* TODO: Consider making the handler safe for IRQ sharing */ 156 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { 157 dht11->edges[dht11->num_edges].ts = iio_get_time_ns(); 158 dht11->edges[dht11->num_edges++].value = 159 gpio_get_value(dht11->gpio); 160 161 if (dht11->num_edges >= DHT11_EDGES_PER_READ) 162 complete(&dht11->completion); 163 } 164 165 return IRQ_HANDLED; 166 } 167 168 static int dht11_read_raw(struct iio_dev *iio_dev, 169 const struct iio_chan_spec *chan, 170 int *val, int *val2, long m) 171 { 172 struct dht11 *dht11 = iio_priv(iio_dev); 173 int ret; 174 175 mutex_lock(&dht11->lock); 176 if (dht11->timestamp + DHT11_DATA_VALID_TIME < iio_get_time_ns()) { 177 reinit_completion(&dht11->completion); 178 179 dht11->num_edges = 0; 180 ret = gpio_direction_output(dht11->gpio, 0); 181 if (ret) 182 goto err; 183 msleep(DHT11_START_TRANSMISSION); 184 ret = gpio_direction_input(dht11->gpio); 185 if (ret) 186 goto err; 187 188 ret = request_irq(dht11->irq, dht11_handle_irq, 189 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, 190 iio_dev->name, iio_dev); 191 if (ret) 192 goto err; 193 194 ret = wait_for_completion_killable_timeout(&dht11->completion, 195 HZ); 196 197 free_irq(dht11->irq, iio_dev); 198 199 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { 200 dev_err(&iio_dev->dev, 201 "Only %d signal edges detected\n", 202 dht11->num_edges); 203 ret = -ETIMEDOUT; 204 } 205 if (ret < 0) 206 goto err; 207 208 ret = dht11_decode(dht11, 209 dht11->num_edges == DHT11_EDGES_PER_READ ? 210 DHT11_EDGES_PREAMBLE : 211 DHT11_EDGES_PREAMBLE - 2); 212 if (ret) 213 goto err; 214 } 215 216 ret = IIO_VAL_INT; 217 if (chan->type == IIO_TEMP) 218 *val = dht11->temperature; 219 else if (chan->type == IIO_HUMIDITYRELATIVE) 220 *val = dht11->humidity; 221 else 222 ret = -EINVAL; 223 err: 224 dht11->num_edges = -1; 225 mutex_unlock(&dht11->lock); 226 return ret; 227 } 228 229 static const struct iio_info dht11_iio_info = { 230 .driver_module = THIS_MODULE, 231 .read_raw = dht11_read_raw, 232 }; 233 234 static const struct iio_chan_spec dht11_chan_spec[] = { 235 { .type = IIO_TEMP, 236 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, 237 { .type = IIO_HUMIDITYRELATIVE, 238 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } 239 }; 240 241 static const struct of_device_id dht11_dt_ids[] = { 242 { .compatible = "dht11", }, 243 { } 244 }; 245 MODULE_DEVICE_TABLE(of, dht11_dt_ids); 246 247 static int dht11_probe(struct platform_device *pdev) 248 { 249 struct device *dev = &pdev->dev; 250 struct device_node *node = dev->of_node; 251 struct dht11 *dht11; 252 struct iio_dev *iio; 253 int ret; 254 255 iio = devm_iio_device_alloc(dev, sizeof(*dht11)); 256 if (!iio) { 257 dev_err(dev, "Failed to allocate IIO device\n"); 258 return -ENOMEM; 259 } 260 261 dht11 = iio_priv(iio); 262 dht11->dev = dev; 263 264 dht11->gpio = ret = of_get_gpio(node, 0); 265 if (ret < 0) 266 return ret; 267 ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name); 268 if (ret) 269 return ret; 270 271 dht11->irq = gpio_to_irq(dht11->gpio); 272 if (dht11->irq < 0) { 273 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio); 274 return -EINVAL; 275 } 276 277 dht11->timestamp = iio_get_time_ns() - DHT11_DATA_VALID_TIME - 1; 278 dht11->num_edges = -1; 279 280 platform_set_drvdata(pdev, iio); 281 282 init_completion(&dht11->completion); 283 mutex_init(&dht11->lock); 284 iio->name = pdev->name; 285 iio->dev.parent = &pdev->dev; 286 iio->info = &dht11_iio_info; 287 iio->modes = INDIO_DIRECT_MODE; 288 iio->channels = dht11_chan_spec; 289 iio->num_channels = ARRAY_SIZE(dht11_chan_spec); 290 291 return devm_iio_device_register(dev, iio); 292 } 293 294 static struct platform_driver dht11_driver = { 295 .driver = { 296 .name = DRIVER_NAME, 297 .of_match_table = dht11_dt_ids, 298 }, 299 .probe = dht11_probe, 300 }; 301 302 module_platform_driver(dht11_driver); 303 304 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); 305 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); 306 MODULE_LICENSE("GPL v2"); 307