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/delay.h> 33 #include <linux/gpio.h> 34 #include <linux/of_gpio.h> 35 36 #include <linux/iio/iio.h> 37 38 #define DRIVER_NAME "dht11" 39 40 #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ 41 42 #define DHT11_EDGES_PREAMBLE 4 43 #define DHT11_BITS_PER_READ 40 44 #define DHT11_EDGES_PER_READ (2*DHT11_BITS_PER_READ + DHT11_EDGES_PREAMBLE + 1) 45 46 /* Data transmission timing (nano seconds) */ 47 #define DHT11_START_TRANSMISSION 18 /* ms */ 48 #define DHT11_SENSOR_RESPONSE 80000 49 #define DHT11_START_BIT 50000 50 #define DHT11_DATA_BIT_LOW 27000 51 #define DHT11_DATA_BIT_HIGH 70000 52 53 struct dht11 { 54 struct device *dev; 55 56 int gpio; 57 int irq; 58 59 struct completion completion; 60 61 s64 timestamp; 62 int temperature; 63 int humidity; 64 65 /* num_edges: -1 means "no transmission in progress" */ 66 int num_edges; 67 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; 68 }; 69 70 static unsigned char dht11_decode_byte(int *timing, int threshold) 71 { 72 unsigned char ret = 0; 73 int i; 74 75 for (i = 0; i < 8; ++i) { 76 ret <<= 1; 77 if (timing[i] >= threshold) 78 ++ret; 79 } 80 81 return ret; 82 } 83 84 static int dht11_decode(struct dht11 *dht11, int offset) 85 { 86 int i, t, timing[DHT11_BITS_PER_READ], threshold, 87 timeres = DHT11_SENSOR_RESPONSE; 88 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; 89 90 /* Calculate timestamp resolution */ 91 for (i = 0; i < dht11->num_edges; ++i) { 92 t = dht11->edges[i].ts - dht11->edges[i-1].ts; 93 if (t > 0 && t < timeres) 94 timeres = t; 95 } 96 if (2*timeres > DHT11_DATA_BIT_HIGH) { 97 pr_err("dht11: timeresolution %d too bad for decoding\n", 98 timeres); 99 return -EIO; 100 } 101 threshold = DHT11_DATA_BIT_HIGH / timeres; 102 if (DHT11_DATA_BIT_LOW/timeres + 1 >= threshold) 103 pr_err("dht11: WARNING: decoding ambiguous\n"); 104 105 /* scale down with timeres and check validity */ 106 for (i = 0; i < DHT11_BITS_PER_READ; ++i) { 107 t = dht11->edges[offset + 2*i + 2].ts - 108 dht11->edges[offset + 2*i + 1].ts; 109 if (!dht11->edges[offset + 2*i + 1].value) 110 return -EIO; /* lost synchronisation */ 111 timing[i] = t / timeres; 112 } 113 114 hum_int = dht11_decode_byte(timing, threshold); 115 hum_dec = dht11_decode_byte(&timing[8], threshold); 116 temp_int = dht11_decode_byte(&timing[16], threshold); 117 temp_dec = dht11_decode_byte(&timing[24], threshold); 118 checksum = dht11_decode_byte(&timing[32], threshold); 119 120 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) 121 return -EIO; 122 123 dht11->timestamp = iio_get_time_ns(); 124 if (hum_int < 20) { /* DHT22 */ 125 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * 126 ((temp_int & 0x80) ? -100 : 100); 127 dht11->humidity = ((hum_int << 8) + hum_dec) * 100; 128 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ 129 dht11->temperature = temp_int * 1000; 130 dht11->humidity = hum_int * 1000; 131 } else { 132 dev_err(dht11->dev, 133 "Don't know how to decode data: %d %d %d %d\n", 134 hum_int, hum_dec, temp_int, temp_dec); 135 return -EIO; 136 } 137 138 return 0; 139 } 140 141 static int dht11_read_raw(struct iio_dev *iio_dev, 142 const struct iio_chan_spec *chan, 143 int *val, int *val2, long m) 144 { 145 struct dht11 *dht11 = iio_priv(iio_dev); 146 int ret; 147 148 if (dht11->timestamp + DHT11_DATA_VALID_TIME < iio_get_time_ns()) { 149 reinit_completion(&dht11->completion); 150 151 dht11->num_edges = 0; 152 ret = gpio_direction_output(dht11->gpio, 0); 153 if (ret) 154 goto err; 155 msleep(DHT11_START_TRANSMISSION); 156 ret = gpio_direction_input(dht11->gpio); 157 if (ret) 158 goto err; 159 160 ret = wait_for_completion_killable_timeout(&dht11->completion, 161 HZ); 162 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { 163 dev_err(&iio_dev->dev, 164 "Only %d signal edges detected\n", 165 dht11->num_edges); 166 ret = -ETIMEDOUT; 167 } 168 if (ret < 0) 169 goto err; 170 171 ret = dht11_decode(dht11, 172 dht11->num_edges == DHT11_EDGES_PER_READ ? 173 DHT11_EDGES_PREAMBLE : 174 DHT11_EDGES_PREAMBLE - 2); 175 if (ret) 176 goto err; 177 } 178 179 ret = IIO_VAL_INT; 180 if (chan->type == IIO_TEMP) 181 *val = dht11->temperature; 182 else if (chan->type == IIO_HUMIDITYRELATIVE) 183 *val = dht11->humidity; 184 else 185 ret = -EINVAL; 186 err: 187 dht11->num_edges = -1; 188 return ret; 189 } 190 191 static const struct iio_info dht11_iio_info = { 192 .driver_module = THIS_MODULE, 193 .read_raw = dht11_read_raw, 194 }; 195 196 /* 197 * IRQ handler called on GPIO edges 198 */ 199 static irqreturn_t dht11_handle_irq(int irq, void *data) 200 { 201 struct iio_dev *iio = data; 202 struct dht11 *dht11 = iio_priv(iio); 203 204 /* TODO: Consider making the handler safe for IRQ sharing */ 205 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { 206 dht11->edges[dht11->num_edges].ts = iio_get_time_ns(); 207 dht11->edges[dht11->num_edges++].value = 208 gpio_get_value(dht11->gpio); 209 210 if (dht11->num_edges >= DHT11_EDGES_PER_READ) 211 complete(&dht11->completion); 212 } 213 214 return IRQ_HANDLED; 215 } 216 217 static const struct iio_chan_spec dht11_chan_spec[] = { 218 { .type = IIO_TEMP, 219 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, 220 { .type = IIO_HUMIDITYRELATIVE, 221 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } 222 }; 223 224 static const struct of_device_id dht11_dt_ids[] = { 225 { .compatible = "dht11", }, 226 { } 227 }; 228 MODULE_DEVICE_TABLE(of, dht11_dt_ids); 229 230 static int dht11_probe(struct platform_device *pdev) 231 { 232 struct device *dev = &pdev->dev; 233 struct device_node *node = dev->of_node; 234 struct dht11 *dht11; 235 struct iio_dev *iio; 236 int ret; 237 238 iio = devm_iio_device_alloc(dev, sizeof(*dht11)); 239 if (!iio) { 240 dev_err(dev, "Failed to allocate IIO device\n"); 241 return -ENOMEM; 242 } 243 244 dht11 = iio_priv(iio); 245 dht11->dev = dev; 246 247 dht11->gpio = ret = of_get_gpio(node, 0); 248 if (ret < 0) 249 return ret; 250 ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name); 251 if (ret) 252 return ret; 253 254 dht11->irq = gpio_to_irq(dht11->gpio); 255 if (dht11->irq < 0) { 256 dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio); 257 return -EINVAL; 258 } 259 ret = devm_request_irq(dev, dht11->irq, dht11_handle_irq, 260 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, 261 pdev->name, iio); 262 if (ret) 263 return ret; 264 265 dht11->timestamp = iio_get_time_ns() - DHT11_DATA_VALID_TIME - 1; 266 dht11->num_edges = -1; 267 268 platform_set_drvdata(pdev, iio); 269 270 init_completion(&dht11->completion); 271 iio->name = pdev->name; 272 iio->dev.parent = &pdev->dev; 273 iio->info = &dht11_iio_info; 274 iio->modes = INDIO_DIRECT_MODE; 275 iio->channels = dht11_chan_spec; 276 iio->num_channels = ARRAY_SIZE(dht11_chan_spec); 277 278 return devm_iio_device_register(dev, iio); 279 } 280 281 static struct platform_driver dht11_driver = { 282 .driver = { 283 .name = DRIVER_NAME, 284 .owner = THIS_MODULE, 285 .of_match_table = dht11_dt_ids, 286 }, 287 .probe = dht11_probe, 288 }; 289 290 module_platform_driver(dht11_driver); 291 292 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); 293 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); 294 MODULE_LICENSE("GPL v2"); 295