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 #include <linux/timekeeping.h> 37 38 #include <linux/iio/iio.h> 39 40 #define DRIVER_NAME "dht11" 41 42 #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ 43 44 #define DHT11_EDGES_PREAMBLE 2 45 #define DHT11_BITS_PER_READ 40 46 /* 47 * Note that when reading the sensor actually 84 edges are detected, but 48 * since the last edge is not significant, we only store 83: 49 */ 50 #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \ 51 DHT11_EDGES_PREAMBLE + 1) 52 53 /* Data transmission timing (nano seconds) */ 54 #define DHT11_START_TRANSMISSION 18 /* ms */ 55 #define DHT11_SENSOR_RESPONSE 80000 56 #define DHT11_START_BIT 50000 57 #define DHT11_DATA_BIT_LOW 27000 58 #define DHT11_DATA_BIT_HIGH 70000 59 60 struct dht11 { 61 struct device *dev; 62 63 int gpio; 64 int irq; 65 66 struct completion completion; 67 /* The iio sysfs interface doesn't prevent concurrent reads: */ 68 struct mutex lock; 69 70 s64 timestamp; 71 int temperature; 72 int humidity; 73 74 /* num_edges: -1 means "no transmission in progress" */ 75 int num_edges; 76 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; 77 }; 78 79 static unsigned char dht11_decode_byte(int *timing, int threshold) 80 { 81 unsigned char ret = 0; 82 int i; 83 84 for (i = 0; i < 8; ++i) { 85 ret <<= 1; 86 if (timing[i] >= threshold) 87 ++ret; 88 } 89 90 return ret; 91 } 92 93 static int dht11_decode(struct dht11 *dht11, int offset, int timeres) 94 { 95 int i, t, timing[DHT11_BITS_PER_READ], threshold; 96 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; 97 98 threshold = DHT11_DATA_BIT_HIGH / timeres; 99 if (DHT11_DATA_BIT_LOW / timeres + 1 >= threshold) 100 pr_err("dht11: WARNING: decoding ambiguous\n"); 101 102 /* scale down with timeres and check validity */ 103 for (i = 0; i < DHT11_BITS_PER_READ; ++i) { 104 t = dht11->edges[offset + 2 * i + 2].ts - 105 dht11->edges[offset + 2 * i + 1].ts; 106 if (!dht11->edges[offset + 2 * i + 1].value) 107 return -EIO; /* lost synchronisation */ 108 timing[i] = t / timeres; 109 } 110 111 hum_int = dht11_decode_byte(timing, threshold); 112 hum_dec = dht11_decode_byte(&timing[8], threshold); 113 temp_int = dht11_decode_byte(&timing[16], threshold); 114 temp_dec = dht11_decode_byte(&timing[24], threshold); 115 checksum = dht11_decode_byte(&timing[32], threshold); 116 117 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) 118 return -EIO; 119 120 dht11->timestamp = ktime_get_real_ns(); 121 if (hum_int < 20) { /* DHT22 */ 122 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * 123 ((temp_int & 0x80) ? -100 : 100); 124 dht11->humidity = ((hum_int << 8) + hum_dec) * 100; 125 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ 126 dht11->temperature = temp_int * 1000; 127 dht11->humidity = hum_int * 1000; 128 } else { 129 dev_err(dht11->dev, 130 "Don't know how to decode data: %d %d %d %d\n", 131 hum_int, hum_dec, temp_int, temp_dec); 132 return -EIO; 133 } 134 135 return 0; 136 } 137 138 /* 139 * IRQ handler called on GPIO edges 140 */ 141 static irqreturn_t dht11_handle_irq(int irq, void *data) 142 { 143 struct iio_dev *iio = data; 144 struct dht11 *dht11 = iio_priv(iio); 145 146 /* TODO: Consider making the handler safe for IRQ sharing */ 147 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { 148 dht11->edges[dht11->num_edges].ts = ktime_get_real_ns(); 149 dht11->edges[dht11->num_edges++].value = 150 gpio_get_value(dht11->gpio); 151 152 if (dht11->num_edges >= DHT11_EDGES_PER_READ) 153 complete(&dht11->completion); 154 } 155 156 return IRQ_HANDLED; 157 } 158 159 static int dht11_read_raw(struct iio_dev *iio_dev, 160 const struct iio_chan_spec *chan, 161 int *val, int *val2, long m) 162 { 163 struct dht11 *dht11 = iio_priv(iio_dev); 164 int ret, timeres; 165 166 mutex_lock(&dht11->lock); 167 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_real_ns()) { 168 timeres = ktime_get_resolution_ns(); 169 if (DHT11_DATA_BIT_HIGH < 2 * timeres) { 170 dev_err(dht11->dev, "timeresolution %dns too low\n", 171 timeres); 172 /* In theory a better clock could become available 173 * at some point ... and there is no error code 174 * that really fits better. 175 */ 176 ret = -EAGAIN; 177 goto err; 178 } 179 180 reinit_completion(&dht11->completion); 181 182 dht11->num_edges = 0; 183 ret = gpio_direction_output(dht11->gpio, 0); 184 if (ret) 185 goto err; 186 msleep(DHT11_START_TRANSMISSION); 187 ret = gpio_direction_input(dht11->gpio); 188 if (ret) 189 goto err; 190 191 ret = request_irq(dht11->irq, dht11_handle_irq, 192 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, 193 iio_dev->name, iio_dev); 194 if (ret) 195 goto err; 196 197 ret = wait_for_completion_killable_timeout(&dht11->completion, 198 HZ); 199 200 free_irq(dht11->irq, iio_dev); 201 202 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { 203 dev_err(&iio_dev->dev, 204 "Only %d signal edges detected\n", 205 dht11->num_edges); 206 ret = -ETIMEDOUT; 207 } 208 if (ret < 0) 209 goto err; 210 211 ret = dht11_decode(dht11, 212 dht11->num_edges == DHT11_EDGES_PER_READ ? 213 DHT11_EDGES_PREAMBLE : 214 DHT11_EDGES_PREAMBLE - 2, 215 timeres); 216 if (ret) 217 goto err; 218 } 219 220 ret = IIO_VAL_INT; 221 if (chan->type == IIO_TEMP) 222 *val = dht11->temperature; 223 else if (chan->type == IIO_HUMIDITYRELATIVE) 224 *val = dht11->humidity; 225 else 226 ret = -EINVAL; 227 err: 228 dht11->num_edges = -1; 229 mutex_unlock(&dht11->lock); 230 return ret; 231 } 232 233 static const struct iio_info dht11_iio_info = { 234 .driver_module = THIS_MODULE, 235 .read_raw = dht11_read_raw, 236 }; 237 238 static const struct iio_chan_spec dht11_chan_spec[] = { 239 { .type = IIO_TEMP, 240 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, 241 { .type = IIO_HUMIDITYRELATIVE, 242 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } 243 }; 244 245 static const struct of_device_id dht11_dt_ids[] = { 246 { .compatible = "dht11", }, 247 { } 248 }; 249 MODULE_DEVICE_TABLE(of, dht11_dt_ids); 250 251 static int dht11_probe(struct platform_device *pdev) 252 { 253 struct device *dev = &pdev->dev; 254 struct device_node *node = dev->of_node; 255 struct dht11 *dht11; 256 struct iio_dev *iio; 257 int ret; 258 259 iio = devm_iio_device_alloc(dev, sizeof(*dht11)); 260 if (!iio) { 261 dev_err(dev, "Failed to allocate IIO device\n"); 262 return -ENOMEM; 263 } 264 265 dht11 = iio_priv(iio); 266 dht11->dev = dev; 267 268 ret = of_get_gpio(node, 0); 269 if (ret < 0) 270 return ret; 271 dht11->gpio = ret; 272 ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name); 273 if (ret) 274 return ret; 275 276 dht11->irq = gpio_to_irq(dht11->gpio); 277 if (dht11->irq < 0) { 278 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio); 279 return -EINVAL; 280 } 281 282 dht11->timestamp = ktime_get_real_ns() - DHT11_DATA_VALID_TIME - 1; 283 dht11->num_edges = -1; 284 285 platform_set_drvdata(pdev, iio); 286 287 init_completion(&dht11->completion); 288 mutex_init(&dht11->lock); 289 iio->name = pdev->name; 290 iio->dev.parent = &pdev->dev; 291 iio->info = &dht11_iio_info; 292 iio->modes = INDIO_DIRECT_MODE; 293 iio->channels = dht11_chan_spec; 294 iio->num_channels = ARRAY_SIZE(dht11_chan_spec); 295 296 return devm_iio_device_register(dev, iio); 297 } 298 299 static struct platform_driver dht11_driver = { 300 .driver = { 301 .name = DRIVER_NAME, 302 .of_match_table = dht11_dt_ids, 303 }, 304 .probe = dht11_probe, 305 }; 306 307 module_platform_driver(dht11_driver); 308 309 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); 310 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); 311 MODULE_LICENSE("GPL v2"); 312