1091a121bSHarald Geyer /* 2091a121bSHarald Geyer * DHT11/DHT22 bit banging GPIO driver 3091a121bSHarald Geyer * 4091a121bSHarald Geyer * Copyright (c) Harald Geyer <harald@ccbib.org> 5091a121bSHarald Geyer * 6091a121bSHarald Geyer * This program is free software; you can redistribute it and/or modify 7091a121bSHarald Geyer * it under the terms of the GNU General Public License as published by 8091a121bSHarald Geyer * the Free Software Foundation; either version 2 of the License, or 9091a121bSHarald Geyer * (at your option) any later version. 10091a121bSHarald Geyer * 11091a121bSHarald Geyer * This program is distributed in the hope that it will be useful, 12091a121bSHarald Geyer * but WITHOUT ANY WARRANTY; without even the implied warranty of 13091a121bSHarald Geyer * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14091a121bSHarald Geyer * GNU General Public License for more details. 15091a121bSHarald Geyer */ 16091a121bSHarald Geyer 17091a121bSHarald Geyer #include <linux/err.h> 18091a121bSHarald Geyer #include <linux/interrupt.h> 19091a121bSHarald Geyer #include <linux/device.h> 20091a121bSHarald Geyer #include <linux/kernel.h> 21091a121bSHarald Geyer #include <linux/printk.h> 22091a121bSHarald Geyer #include <linux/slab.h> 23091a121bSHarald Geyer #include <linux/of.h> 24091a121bSHarald Geyer #include <linux/of_device.h> 25091a121bSHarald Geyer #include <linux/sysfs.h> 26091a121bSHarald Geyer #include <linux/io.h> 27091a121bSHarald Geyer #include <linux/module.h> 28091a121bSHarald Geyer #include <linux/platform_device.h> 29091a121bSHarald Geyer #include <linux/wait.h> 30091a121bSHarald Geyer #include <linux/bitops.h> 31091a121bSHarald Geyer #include <linux/completion.h> 32004bc530SRichard Weinberger #include <linux/mutex.h> 33091a121bSHarald Geyer #include <linux/delay.h> 34091a121bSHarald Geyer #include <linux/gpio.h> 35091a121bSHarald Geyer #include <linux/of_gpio.h> 36081d9740SHarald Geyer #include <linux/timekeeping.h> 37091a121bSHarald Geyer 38091a121bSHarald Geyer #include <linux/iio/iio.h> 39091a121bSHarald Geyer 40091a121bSHarald Geyer #define DRIVER_NAME "dht11" 41091a121bSHarald Geyer 42091a121bSHarald Geyer #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ 43091a121bSHarald Geyer 4494e65519SRichard Weinberger #define DHT11_EDGES_PREAMBLE 2 45091a121bSHarald Geyer #define DHT11_BITS_PER_READ 40 4694e65519SRichard Weinberger /* 4794e65519SRichard Weinberger * Note that when reading the sensor actually 84 edges are detected, but 4894e65519SRichard Weinberger * since the last edge is not significant, we only store 83: 4994e65519SRichard Weinberger */ 50889c5e9bSHarald Geyer #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \ 51889c5e9bSHarald Geyer DHT11_EDGES_PREAMBLE + 1) 52091a121bSHarald Geyer 53091a121bSHarald Geyer /* Data transmission timing (nano seconds) */ 54091a121bSHarald Geyer #define DHT11_START_TRANSMISSION 18 /* ms */ 55091a121bSHarald Geyer #define DHT11_SENSOR_RESPONSE 80000 56091a121bSHarald Geyer #define DHT11_START_BIT 50000 57091a121bSHarald Geyer #define DHT11_DATA_BIT_LOW 27000 58091a121bSHarald Geyer #define DHT11_DATA_BIT_HIGH 70000 59091a121bSHarald Geyer 60091a121bSHarald Geyer struct dht11 { 61091a121bSHarald Geyer struct device *dev; 62091a121bSHarald Geyer 63091a121bSHarald Geyer int gpio; 64091a121bSHarald Geyer int irq; 65091a121bSHarald Geyer 66091a121bSHarald Geyer struct completion completion; 67a7126003SHarald Geyer /* The iio sysfs interface doesn't prevent concurrent reads: */ 68004bc530SRichard Weinberger struct mutex lock; 69091a121bSHarald Geyer 70091a121bSHarald Geyer s64 timestamp; 71091a121bSHarald Geyer int temperature; 72091a121bSHarald Geyer int humidity; 73091a121bSHarald Geyer 74091a121bSHarald Geyer /* num_edges: -1 means "no transmission in progress" */ 75091a121bSHarald Geyer int num_edges; 76091a121bSHarald Geyer struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; 77091a121bSHarald Geyer }; 78091a121bSHarald Geyer 79091a121bSHarald Geyer static unsigned char dht11_decode_byte(int *timing, int threshold) 80091a121bSHarald Geyer { 81091a121bSHarald Geyer unsigned char ret = 0; 82091a121bSHarald Geyer int i; 83091a121bSHarald Geyer 84091a121bSHarald Geyer for (i = 0; i < 8; ++i) { 85091a121bSHarald Geyer ret <<= 1; 86091a121bSHarald Geyer if (timing[i] >= threshold) 87091a121bSHarald Geyer ++ret; 88091a121bSHarald Geyer } 89091a121bSHarald Geyer 90091a121bSHarald Geyer return ret; 91091a121bSHarald Geyer } 92091a121bSHarald Geyer 93081d9740SHarald Geyer static int dht11_decode(struct dht11 *dht11, int offset, int timeres) 94091a121bSHarald Geyer { 95081d9740SHarald Geyer int i, t, timing[DHT11_BITS_PER_READ], threshold; 96091a121bSHarald Geyer unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; 97091a121bSHarald Geyer 98091a121bSHarald Geyer threshold = DHT11_DATA_BIT_HIGH / timeres; 99091a121bSHarald Geyer if (DHT11_DATA_BIT_LOW / timeres + 1 >= threshold) 100091a121bSHarald Geyer pr_err("dht11: WARNING: decoding ambiguous\n"); 101091a121bSHarald Geyer 102091a121bSHarald Geyer /* scale down with timeres and check validity */ 103091a121bSHarald Geyer for (i = 0; i < DHT11_BITS_PER_READ; ++i) { 104091a121bSHarald Geyer t = dht11->edges[offset + 2 * i + 2].ts - 105091a121bSHarald Geyer dht11->edges[offset + 2 * i + 1].ts; 106091a121bSHarald Geyer if (!dht11->edges[offset + 2 * i + 1].value) 107091a121bSHarald Geyer return -EIO; /* lost synchronisation */ 108091a121bSHarald Geyer timing[i] = t / timeres; 109091a121bSHarald Geyer } 110091a121bSHarald Geyer 111091a121bSHarald Geyer hum_int = dht11_decode_byte(timing, threshold); 112091a121bSHarald Geyer hum_dec = dht11_decode_byte(&timing[8], threshold); 113091a121bSHarald Geyer temp_int = dht11_decode_byte(&timing[16], threshold); 114091a121bSHarald Geyer temp_dec = dht11_decode_byte(&timing[24], threshold); 115091a121bSHarald Geyer checksum = dht11_decode_byte(&timing[32], threshold); 116091a121bSHarald Geyer 117091a121bSHarald Geyer if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) 118091a121bSHarald Geyer return -EIO; 119091a121bSHarald Geyer 12017a2f46cSAbhilash Jindal dht11->timestamp = ktime_get_boot_ns(); 121091a121bSHarald Geyer if (hum_int < 20) { /* DHT22 */ 122091a121bSHarald Geyer dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * 123091a121bSHarald Geyer ((temp_int & 0x80) ? -100 : 100); 124091a121bSHarald Geyer dht11->humidity = ((hum_int << 8) + hum_dec) * 100; 125091a121bSHarald Geyer } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ 126091a121bSHarald Geyer dht11->temperature = temp_int * 1000; 127091a121bSHarald Geyer dht11->humidity = hum_int * 1000; 128091a121bSHarald Geyer } else { 129091a121bSHarald Geyer dev_err(dht11->dev, 130091a121bSHarald Geyer "Don't know how to decode data: %d %d %d %d\n", 131091a121bSHarald Geyer hum_int, hum_dec, temp_int, temp_dec); 132091a121bSHarald Geyer return -EIO; 133091a121bSHarald Geyer } 134091a121bSHarald Geyer 135091a121bSHarald Geyer return 0; 136091a121bSHarald Geyer } 137091a121bSHarald Geyer 13894e65519SRichard Weinberger /* 13994e65519SRichard Weinberger * IRQ handler called on GPIO edges 14094e65519SRichard Weinberger */ 14194e65519SRichard Weinberger static irqreturn_t dht11_handle_irq(int irq, void *data) 14294e65519SRichard Weinberger { 14394e65519SRichard Weinberger struct iio_dev *iio = data; 14494e65519SRichard Weinberger struct dht11 *dht11 = iio_priv(iio); 14594e65519SRichard Weinberger 14694e65519SRichard Weinberger /* TODO: Consider making the handler safe for IRQ sharing */ 14794e65519SRichard Weinberger if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { 14817a2f46cSAbhilash Jindal dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns(); 14994e65519SRichard Weinberger dht11->edges[dht11->num_edges++].value = 15094e65519SRichard Weinberger gpio_get_value(dht11->gpio); 15194e65519SRichard Weinberger 15294e65519SRichard Weinberger if (dht11->num_edges >= DHT11_EDGES_PER_READ) 15394e65519SRichard Weinberger complete(&dht11->completion); 15494e65519SRichard Weinberger } 15594e65519SRichard Weinberger 15694e65519SRichard Weinberger return IRQ_HANDLED; 15794e65519SRichard Weinberger } 15894e65519SRichard Weinberger 159091a121bSHarald Geyer static int dht11_read_raw(struct iio_dev *iio_dev, 160091a121bSHarald Geyer const struct iio_chan_spec *chan, 161091a121bSHarald Geyer int *val, int *val2, long m) 162091a121bSHarald Geyer { 163091a121bSHarald Geyer struct dht11 *dht11 = iio_priv(iio_dev); 164081d9740SHarald Geyer int ret, timeres; 165091a121bSHarald Geyer 166004bc530SRichard Weinberger mutex_lock(&dht11->lock); 16717a2f46cSAbhilash Jindal if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) { 168081d9740SHarald Geyer timeres = ktime_get_resolution_ns(); 169081d9740SHarald Geyer if (DHT11_DATA_BIT_HIGH < 2 * timeres) { 170081d9740SHarald Geyer dev_err(dht11->dev, "timeresolution %dns too low\n", 171081d9740SHarald Geyer timeres); 172081d9740SHarald Geyer /* In theory a better clock could become available 173081d9740SHarald Geyer * at some point ... and there is no error code 174081d9740SHarald Geyer * that really fits better. 175081d9740SHarald Geyer */ 176081d9740SHarald Geyer ret = -EAGAIN; 177081d9740SHarald Geyer goto err; 178081d9740SHarald Geyer } 179081d9740SHarald Geyer 180091a121bSHarald Geyer reinit_completion(&dht11->completion); 181091a121bSHarald Geyer 182091a121bSHarald Geyer dht11->num_edges = 0; 183091a121bSHarald Geyer ret = gpio_direction_output(dht11->gpio, 0); 184091a121bSHarald Geyer if (ret) 185091a121bSHarald Geyer goto err; 186091a121bSHarald Geyer msleep(DHT11_START_TRANSMISSION); 187091a121bSHarald Geyer ret = gpio_direction_input(dht11->gpio); 188091a121bSHarald Geyer if (ret) 189091a121bSHarald Geyer goto err; 190091a121bSHarald Geyer 19194e65519SRichard Weinberger ret = request_irq(dht11->irq, dht11_handle_irq, 19294e65519SRichard Weinberger IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, 19394e65519SRichard Weinberger iio_dev->name, iio_dev); 19494e65519SRichard Weinberger if (ret) 19594e65519SRichard Weinberger goto err; 19694e65519SRichard Weinberger 197091a121bSHarald Geyer ret = wait_for_completion_killable_timeout(&dht11->completion, 198091a121bSHarald Geyer HZ); 19994e65519SRichard Weinberger 20094e65519SRichard Weinberger free_irq(dht11->irq, iio_dev); 20194e65519SRichard Weinberger 202091a121bSHarald Geyer if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { 203091a121bSHarald Geyer dev_err(&iio_dev->dev, 204091a121bSHarald Geyer "Only %d signal edges detected\n", 205091a121bSHarald Geyer dht11->num_edges); 206091a121bSHarald Geyer ret = -ETIMEDOUT; 207091a121bSHarald Geyer } 208091a121bSHarald Geyer if (ret < 0) 209091a121bSHarald Geyer goto err; 210091a121bSHarald Geyer 211091a121bSHarald Geyer ret = dht11_decode(dht11, 212091a121bSHarald Geyer dht11->num_edges == DHT11_EDGES_PER_READ ? 213091a121bSHarald Geyer DHT11_EDGES_PREAMBLE : 214081d9740SHarald Geyer DHT11_EDGES_PREAMBLE - 2, 215081d9740SHarald Geyer timeres); 216091a121bSHarald Geyer if (ret) 217091a121bSHarald Geyer goto err; 218091a121bSHarald Geyer } 219091a121bSHarald Geyer 220091a121bSHarald Geyer ret = IIO_VAL_INT; 221091a121bSHarald Geyer if (chan->type == IIO_TEMP) 222091a121bSHarald Geyer *val = dht11->temperature; 223091a121bSHarald Geyer else if (chan->type == IIO_HUMIDITYRELATIVE) 224091a121bSHarald Geyer *val = dht11->humidity; 225091a121bSHarald Geyer else 226091a121bSHarald Geyer ret = -EINVAL; 227091a121bSHarald Geyer err: 228091a121bSHarald Geyer dht11->num_edges = -1; 229004bc530SRichard Weinberger mutex_unlock(&dht11->lock); 230091a121bSHarald Geyer return ret; 231091a121bSHarald Geyer } 232091a121bSHarald Geyer 233091a121bSHarald Geyer static const struct iio_info dht11_iio_info = { 234091a121bSHarald Geyer .driver_module = THIS_MODULE, 235091a121bSHarald Geyer .read_raw = dht11_read_raw, 236091a121bSHarald Geyer }; 237091a121bSHarald Geyer 238091a121bSHarald Geyer static const struct iio_chan_spec dht11_chan_spec[] = { 239091a121bSHarald Geyer { .type = IIO_TEMP, 240091a121bSHarald Geyer .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, 241091a121bSHarald Geyer { .type = IIO_HUMIDITYRELATIVE, 242091a121bSHarald Geyer .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } 243091a121bSHarald Geyer }; 244091a121bSHarald Geyer 245091a121bSHarald Geyer static const struct of_device_id dht11_dt_ids[] = { 246091a121bSHarald Geyer { .compatible = "dht11", }, 247091a121bSHarald Geyer { } 248091a121bSHarald Geyer }; 249091a121bSHarald Geyer MODULE_DEVICE_TABLE(of, dht11_dt_ids); 250091a121bSHarald Geyer 251091a121bSHarald Geyer static int dht11_probe(struct platform_device *pdev) 252091a121bSHarald Geyer { 253091a121bSHarald Geyer struct device *dev = &pdev->dev; 254091a121bSHarald Geyer struct device_node *node = dev->of_node; 255091a121bSHarald Geyer struct dht11 *dht11; 256091a121bSHarald Geyer struct iio_dev *iio; 257091a121bSHarald Geyer int ret; 258091a121bSHarald Geyer 259091a121bSHarald Geyer iio = devm_iio_device_alloc(dev, sizeof(*dht11)); 260091a121bSHarald Geyer if (!iio) { 261091a121bSHarald Geyer dev_err(dev, "Failed to allocate IIO device\n"); 262091a121bSHarald Geyer return -ENOMEM; 263091a121bSHarald Geyer } 264091a121bSHarald Geyer 265091a121bSHarald Geyer dht11 = iio_priv(iio); 266091a121bSHarald Geyer dht11->dev = dev; 267091a121bSHarald Geyer 2685fbb0bc4SHarald Geyer ret = of_get_gpio(node, 0); 269091a121bSHarald Geyer if (ret < 0) 270091a121bSHarald Geyer return ret; 2715fbb0bc4SHarald Geyer dht11->gpio = ret; 272091a121bSHarald Geyer ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name); 273091a121bSHarald Geyer if (ret) 274091a121bSHarald Geyer return ret; 275091a121bSHarald Geyer 276091a121bSHarald Geyer dht11->irq = gpio_to_irq(dht11->gpio); 277091a121bSHarald Geyer if (dht11->irq < 0) { 278091a121bSHarald Geyer dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio); 279091a121bSHarald Geyer return -EINVAL; 280091a121bSHarald Geyer } 281091a121bSHarald Geyer 28217a2f46cSAbhilash Jindal dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1; 283091a121bSHarald Geyer dht11->num_edges = -1; 284091a121bSHarald Geyer 285091a121bSHarald Geyer platform_set_drvdata(pdev, iio); 286091a121bSHarald Geyer 287091a121bSHarald Geyer init_completion(&dht11->completion); 288004bc530SRichard Weinberger mutex_init(&dht11->lock); 289091a121bSHarald Geyer iio->name = pdev->name; 290091a121bSHarald Geyer iio->dev.parent = &pdev->dev; 291091a121bSHarald Geyer iio->info = &dht11_iio_info; 292091a121bSHarald Geyer iio->modes = INDIO_DIRECT_MODE; 293091a121bSHarald Geyer iio->channels = dht11_chan_spec; 294091a121bSHarald Geyer iio->num_channels = ARRAY_SIZE(dht11_chan_spec); 295091a121bSHarald Geyer 296091a121bSHarald Geyer return devm_iio_device_register(dev, iio); 297091a121bSHarald Geyer } 298091a121bSHarald Geyer 299091a121bSHarald Geyer static struct platform_driver dht11_driver = { 300091a121bSHarald Geyer .driver = { 301091a121bSHarald Geyer .name = DRIVER_NAME, 302091a121bSHarald Geyer .of_match_table = dht11_dt_ids, 303091a121bSHarald Geyer }, 304091a121bSHarald Geyer .probe = dht11_probe, 305091a121bSHarald Geyer }; 306091a121bSHarald Geyer 307091a121bSHarald Geyer module_platform_driver(dht11_driver); 308091a121bSHarald Geyer 309091a121bSHarald Geyer MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); 310091a121bSHarald Geyer MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); 311091a121bSHarald Geyer MODULE_LICENSE("GPL v2"); 312