1c942fddfSThomas Gleixner // SPDX-License-Identifier: GPL-2.0-or-later 2091a121bSHarald Geyer /* 3091a121bSHarald Geyer * DHT11/DHT22 bit banging GPIO driver 4091a121bSHarald Geyer * 5091a121bSHarald Geyer * Copyright (c) Harald Geyer <harald@ccbib.org> 6091a121bSHarald Geyer */ 7091a121bSHarald Geyer 8091a121bSHarald Geyer #include <linux/err.h> 9091a121bSHarald Geyer #include <linux/interrupt.h> 10091a121bSHarald Geyer #include <linux/device.h> 11091a121bSHarald Geyer #include <linux/kernel.h> 12091a121bSHarald Geyer #include <linux/printk.h> 13091a121bSHarald Geyer #include <linux/slab.h> 14091a121bSHarald Geyer #include <linux/of.h> 15091a121bSHarald Geyer #include <linux/of_device.h> 16091a121bSHarald Geyer #include <linux/sysfs.h> 17091a121bSHarald Geyer #include <linux/io.h> 18091a121bSHarald Geyer #include <linux/module.h> 19091a121bSHarald Geyer #include <linux/platform_device.h> 20091a121bSHarald Geyer #include <linux/wait.h> 21091a121bSHarald Geyer #include <linux/bitops.h> 22091a121bSHarald Geyer #include <linux/completion.h> 23004bc530SRichard Weinberger #include <linux/mutex.h> 24091a121bSHarald Geyer #include <linux/delay.h> 25091a121bSHarald Geyer #include <linux/gpio.h> 26091a121bSHarald Geyer #include <linux/of_gpio.h> 27081d9740SHarald Geyer #include <linux/timekeeping.h> 28091a121bSHarald Geyer 29091a121bSHarald Geyer #include <linux/iio/iio.h> 30091a121bSHarald Geyer 31091a121bSHarald Geyer #define DRIVER_NAME "dht11" 32091a121bSHarald Geyer 33091a121bSHarald Geyer #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ 34091a121bSHarald Geyer 3594e65519SRichard Weinberger #define DHT11_EDGES_PREAMBLE 2 36091a121bSHarald Geyer #define DHT11_BITS_PER_READ 40 3794e65519SRichard Weinberger /* 3894e65519SRichard Weinberger * Note that when reading the sensor actually 84 edges are detected, but 3994e65519SRichard Weinberger * since the last edge is not significant, we only store 83: 4094e65519SRichard Weinberger */ 41889c5e9bSHarald Geyer #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \ 42889c5e9bSHarald Geyer DHT11_EDGES_PREAMBLE + 1) 43091a121bSHarald Geyer 44155a5759SHarald Geyer /* 45155a5759SHarald Geyer * Data transmission timing: 46155a5759SHarald Geyer * Data bits are encoded as pulse length (high time) on the data line. 47155a5759SHarald Geyer * 0-bit: 22-30uS -- typically 26uS (AM2302) 48155a5759SHarald Geyer * 1-bit: 68-75uS -- typically 70uS (AM2302) 49155a5759SHarald Geyer * The acutal timings also depend on the properties of the cable, with 50155a5759SHarald Geyer * longer cables typically making pulses shorter. 51155a5759SHarald Geyer * 52155a5759SHarald Geyer * Our decoding depends on the time resolution of the system: 53155a5759SHarald Geyer * timeres > 34uS ... don't know what a 1-tick pulse is 54155a5759SHarald Geyer * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks) 55155a5759SHarald Geyer * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is 56155a5759SHarald Geyer * timeres < 23uS ... no problem 57155a5759SHarald Geyer * 58155a5759SHarald Geyer * Luckily clocks in the 33-44kHz range are quite uncommon, so we can 59155a5759SHarald Geyer * support most systems if the threshold for decoding a pulse as 1-bit 60155a5759SHarald Geyer * is chosen carefully. If somebody really wants to support clocks around 61155a5759SHarald Geyer * 40kHz, where this driver is most unreliable, there are two options. 62155a5759SHarald Geyer * a) select an implementation using busy loop polling on those systems 63155a5759SHarald Geyer * b) use the checksum to do some probabilistic decoding 64155a5759SHarald Geyer */ 655c113b5eSJohn Brooks #define DHT11_START_TRANSMISSION_MIN 18000 /* us */ 665c113b5eSJohn Brooks #define DHT11_START_TRANSMISSION_MAX 20000 /* us */ 67155a5759SHarald Geyer #define DHT11_MIN_TIMERES 34000 /* ns */ 68155a5759SHarald Geyer #define DHT11_THRESHOLD 49000 /* ns */ 69155a5759SHarald Geyer #define DHT11_AMBIG_LOW 23000 /* ns */ 70155a5759SHarald Geyer #define DHT11_AMBIG_HIGH 30000 /* ns */ 71091a121bSHarald Geyer 72091a121bSHarald Geyer struct dht11 { 73091a121bSHarald Geyer struct device *dev; 74091a121bSHarald Geyer 75091a121bSHarald Geyer int gpio; 76091a121bSHarald Geyer int irq; 77091a121bSHarald Geyer 78091a121bSHarald Geyer struct completion completion; 79a7126003SHarald Geyer /* The iio sysfs interface doesn't prevent concurrent reads: */ 80004bc530SRichard Weinberger struct mutex lock; 81091a121bSHarald Geyer 82091a121bSHarald Geyer s64 timestamp; 83091a121bSHarald Geyer int temperature; 84091a121bSHarald Geyer int humidity; 85091a121bSHarald Geyer 86091a121bSHarald Geyer /* num_edges: -1 means "no transmission in progress" */ 87091a121bSHarald Geyer int num_edges; 88091a121bSHarald Geyer struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; 89091a121bSHarald Geyer }; 90091a121bSHarald Geyer 91ab4b6496SHarald Geyer #ifdef CONFIG_DYNAMIC_DEBUG 92ab4b6496SHarald Geyer /* 93ab4b6496SHarald Geyer * dht11_edges_print: show the data as actually received by the 94ab4b6496SHarald Geyer * driver. 95ab4b6496SHarald Geyer */ 96ab4b6496SHarald Geyer static void dht11_edges_print(struct dht11 *dht11) 97ab4b6496SHarald Geyer { 98ab4b6496SHarald Geyer int i; 99ab4b6496SHarald Geyer 100ab4b6496SHarald Geyer dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges); 101ab4b6496SHarald Geyer for (i = 1; i < dht11->num_edges; ++i) { 102ab4b6496SHarald Geyer dev_dbg(dht11->dev, "%d: %lld ns %s\n", i, 103ab4b6496SHarald Geyer dht11->edges[i].ts - dht11->edges[i - 1].ts, 104ab4b6496SHarald Geyer dht11->edges[i - 1].value ? "high" : "low"); 105ab4b6496SHarald Geyer } 106ab4b6496SHarald Geyer } 107ab4b6496SHarald Geyer #endif /* CONFIG_DYNAMIC_DEBUG */ 108ab4b6496SHarald Geyer 109155a5759SHarald Geyer static unsigned char dht11_decode_byte(char *bits) 110091a121bSHarald Geyer { 111091a121bSHarald Geyer unsigned char ret = 0; 112091a121bSHarald Geyer int i; 113091a121bSHarald Geyer 114091a121bSHarald Geyer for (i = 0; i < 8; ++i) { 115091a121bSHarald Geyer ret <<= 1; 116155a5759SHarald Geyer if (bits[i]) 117091a121bSHarald Geyer ++ret; 118091a121bSHarald Geyer } 119091a121bSHarald Geyer 120091a121bSHarald Geyer return ret; 121091a121bSHarald Geyer } 122091a121bSHarald Geyer 123155a5759SHarald Geyer static int dht11_decode(struct dht11 *dht11, int offset) 124091a121bSHarald Geyer { 125155a5759SHarald Geyer int i, t; 126155a5759SHarald Geyer char bits[DHT11_BITS_PER_READ]; 127091a121bSHarald Geyer unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; 128091a121bSHarald Geyer 129091a121bSHarald Geyer for (i = 0; i < DHT11_BITS_PER_READ; ++i) { 130091a121bSHarald Geyer t = dht11->edges[offset + 2 * i + 2].ts - 131091a121bSHarald Geyer dht11->edges[offset + 2 * i + 1].ts; 132ab4b6496SHarald Geyer if (!dht11->edges[offset + 2 * i + 1].value) { 133ab4b6496SHarald Geyer dev_dbg(dht11->dev, 134ab4b6496SHarald Geyer "lost synchronisation at edge %d\n", 135ab4b6496SHarald Geyer offset + 2 * i + 1); 136ab4b6496SHarald Geyer return -EIO; 137ab4b6496SHarald Geyer } 138155a5759SHarald Geyer bits[i] = t > DHT11_THRESHOLD; 139091a121bSHarald Geyer } 140091a121bSHarald Geyer 141155a5759SHarald Geyer hum_int = dht11_decode_byte(bits); 142155a5759SHarald Geyer hum_dec = dht11_decode_byte(&bits[8]); 143155a5759SHarald Geyer temp_int = dht11_decode_byte(&bits[16]); 144155a5759SHarald Geyer temp_dec = dht11_decode_byte(&bits[24]); 145155a5759SHarald Geyer checksum = dht11_decode_byte(&bits[32]); 146091a121bSHarald Geyer 147ab4b6496SHarald Geyer if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) { 148ab4b6496SHarald Geyer dev_dbg(dht11->dev, "invalid checksum\n"); 149091a121bSHarald Geyer return -EIO; 150ab4b6496SHarald Geyer } 151091a121bSHarald Geyer 15217a2f46cSAbhilash Jindal dht11->timestamp = ktime_get_boot_ns(); 153a6bffb69SHarald Geyer if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */ 154091a121bSHarald Geyer dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * 155091a121bSHarald Geyer ((temp_int & 0x80) ? -100 : 100); 156091a121bSHarald Geyer dht11->humidity = ((hum_int << 8) + hum_dec) * 100; 157091a121bSHarald Geyer } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ 158091a121bSHarald Geyer dht11->temperature = temp_int * 1000; 159091a121bSHarald Geyer dht11->humidity = hum_int * 1000; 160091a121bSHarald Geyer } else { 161091a121bSHarald Geyer dev_err(dht11->dev, 162091a121bSHarald Geyer "Don't know how to decode data: %d %d %d %d\n", 163091a121bSHarald Geyer hum_int, hum_dec, temp_int, temp_dec); 164091a121bSHarald Geyer return -EIO; 165091a121bSHarald Geyer } 166091a121bSHarald Geyer 167091a121bSHarald Geyer return 0; 168091a121bSHarald Geyer } 169091a121bSHarald Geyer 17094e65519SRichard Weinberger /* 17194e65519SRichard Weinberger * IRQ handler called on GPIO edges 17294e65519SRichard Weinberger */ 17394e65519SRichard Weinberger static irqreturn_t dht11_handle_irq(int irq, void *data) 17494e65519SRichard Weinberger { 17594e65519SRichard Weinberger struct iio_dev *iio = data; 17694e65519SRichard Weinberger struct dht11 *dht11 = iio_priv(iio); 17794e65519SRichard Weinberger 17894e65519SRichard Weinberger /* TODO: Consider making the handler safe for IRQ sharing */ 17994e65519SRichard Weinberger if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { 18017a2f46cSAbhilash Jindal dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns(); 18194e65519SRichard Weinberger dht11->edges[dht11->num_edges++].value = 18294e65519SRichard Weinberger gpio_get_value(dht11->gpio); 18394e65519SRichard Weinberger 18494e65519SRichard Weinberger if (dht11->num_edges >= DHT11_EDGES_PER_READ) 18594e65519SRichard Weinberger complete(&dht11->completion); 18694e65519SRichard Weinberger } 18794e65519SRichard Weinberger 18894e65519SRichard Weinberger return IRQ_HANDLED; 18994e65519SRichard Weinberger } 19094e65519SRichard Weinberger 191091a121bSHarald Geyer static int dht11_read_raw(struct iio_dev *iio_dev, 192091a121bSHarald Geyer const struct iio_chan_spec *chan, 193091a121bSHarald Geyer int *val, int *val2, long m) 194091a121bSHarald Geyer { 195091a121bSHarald Geyer struct dht11 *dht11 = iio_priv(iio_dev); 19622acc120SHarald Geyer int ret, timeres, offset; 197091a121bSHarald Geyer 198004bc530SRichard Weinberger mutex_lock(&dht11->lock); 19917a2f46cSAbhilash Jindal if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) { 200081d9740SHarald Geyer timeres = ktime_get_resolution_ns(); 201ab4b6496SHarald Geyer dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres); 202155a5759SHarald Geyer if (timeres > DHT11_MIN_TIMERES) { 203081d9740SHarald Geyer dev_err(dht11->dev, "timeresolution %dns too low\n", 204081d9740SHarald Geyer timeres); 205081d9740SHarald Geyer /* In theory a better clock could become available 206081d9740SHarald Geyer * at some point ... and there is no error code 207081d9740SHarald Geyer * that really fits better. 208081d9740SHarald Geyer */ 209081d9740SHarald Geyer ret = -EAGAIN; 210081d9740SHarald Geyer goto err; 211081d9740SHarald Geyer } 212155a5759SHarald Geyer if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH) 213155a5759SHarald Geyer dev_warn(dht11->dev, 214155a5759SHarald Geyer "timeresolution: %dns - decoding ambiguous\n", 215155a5759SHarald Geyer timeres); 216081d9740SHarald Geyer 217091a121bSHarald Geyer reinit_completion(&dht11->completion); 218091a121bSHarald Geyer 219091a121bSHarald Geyer dht11->num_edges = 0; 220091a121bSHarald Geyer ret = gpio_direction_output(dht11->gpio, 0); 221091a121bSHarald Geyer if (ret) 222091a121bSHarald Geyer goto err; 2235c113b5eSJohn Brooks usleep_range(DHT11_START_TRANSMISSION_MIN, 2245c113b5eSJohn Brooks DHT11_START_TRANSMISSION_MAX); 225091a121bSHarald Geyer ret = gpio_direction_input(dht11->gpio); 226091a121bSHarald Geyer if (ret) 227091a121bSHarald Geyer goto err; 228091a121bSHarald Geyer 22994e65519SRichard Weinberger ret = request_irq(dht11->irq, dht11_handle_irq, 23094e65519SRichard Weinberger IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, 23194e65519SRichard Weinberger iio_dev->name, iio_dev); 23294e65519SRichard Weinberger if (ret) 23394e65519SRichard Weinberger goto err; 23494e65519SRichard Weinberger 235091a121bSHarald Geyer ret = wait_for_completion_killable_timeout(&dht11->completion, 236091a121bSHarald Geyer HZ); 23794e65519SRichard Weinberger 23894e65519SRichard Weinberger free_irq(dht11->irq, iio_dev); 23994e65519SRichard Weinberger 240ab4b6496SHarald Geyer #ifdef CONFIG_DYNAMIC_DEBUG 241ab4b6496SHarald Geyer dht11_edges_print(dht11); 242ab4b6496SHarald Geyer #endif 243ab4b6496SHarald Geyer 244091a121bSHarald Geyer if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { 245ab4b6496SHarald Geyer dev_err(dht11->dev, "Only %d signal edges detected\n", 246091a121bSHarald Geyer dht11->num_edges); 247091a121bSHarald Geyer ret = -ETIMEDOUT; 248091a121bSHarald Geyer } 249091a121bSHarald Geyer if (ret < 0) 250091a121bSHarald Geyer goto err; 251091a121bSHarald Geyer 25222acc120SHarald Geyer offset = DHT11_EDGES_PREAMBLE + 25322acc120SHarald Geyer dht11->num_edges - DHT11_EDGES_PER_READ; 25422acc120SHarald Geyer for (; offset >= 0; --offset) { 255155a5759SHarald Geyer ret = dht11_decode(dht11, offset); 25622acc120SHarald Geyer if (!ret) 25722acc120SHarald Geyer break; 25822acc120SHarald Geyer } 25922acc120SHarald Geyer 260091a121bSHarald Geyer if (ret) 261091a121bSHarald Geyer goto err; 262091a121bSHarald Geyer } 263091a121bSHarald Geyer 264091a121bSHarald Geyer ret = IIO_VAL_INT; 265091a121bSHarald Geyer if (chan->type == IIO_TEMP) 266091a121bSHarald Geyer *val = dht11->temperature; 267091a121bSHarald Geyer else if (chan->type == IIO_HUMIDITYRELATIVE) 268091a121bSHarald Geyer *val = dht11->humidity; 269091a121bSHarald Geyer else 270091a121bSHarald Geyer ret = -EINVAL; 271091a121bSHarald Geyer err: 272091a121bSHarald Geyer dht11->num_edges = -1; 273004bc530SRichard Weinberger mutex_unlock(&dht11->lock); 274091a121bSHarald Geyer return ret; 275091a121bSHarald Geyer } 276091a121bSHarald Geyer 277091a121bSHarald Geyer static const struct iio_info dht11_iio_info = { 278091a121bSHarald Geyer .read_raw = dht11_read_raw, 279091a121bSHarald Geyer }; 280091a121bSHarald Geyer 281091a121bSHarald Geyer static const struct iio_chan_spec dht11_chan_spec[] = { 282091a121bSHarald Geyer { .type = IIO_TEMP, 283091a121bSHarald Geyer .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, 284091a121bSHarald Geyer { .type = IIO_HUMIDITYRELATIVE, 285091a121bSHarald Geyer .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } 286091a121bSHarald Geyer }; 287091a121bSHarald Geyer 288091a121bSHarald Geyer static const struct of_device_id dht11_dt_ids[] = { 289091a121bSHarald Geyer { .compatible = "dht11", }, 290091a121bSHarald Geyer { } 291091a121bSHarald Geyer }; 292091a121bSHarald Geyer MODULE_DEVICE_TABLE(of, dht11_dt_ids); 293091a121bSHarald Geyer 294091a121bSHarald Geyer static int dht11_probe(struct platform_device *pdev) 295091a121bSHarald Geyer { 296091a121bSHarald Geyer struct device *dev = &pdev->dev; 297091a121bSHarald Geyer struct device_node *node = dev->of_node; 298091a121bSHarald Geyer struct dht11 *dht11; 299091a121bSHarald Geyer struct iio_dev *iio; 300091a121bSHarald Geyer int ret; 301091a121bSHarald Geyer 302091a121bSHarald Geyer iio = devm_iio_device_alloc(dev, sizeof(*dht11)); 303091a121bSHarald Geyer if (!iio) { 304091a121bSHarald Geyer dev_err(dev, "Failed to allocate IIO device\n"); 305091a121bSHarald Geyer return -ENOMEM; 306091a121bSHarald Geyer } 307091a121bSHarald Geyer 308091a121bSHarald Geyer dht11 = iio_priv(iio); 309091a121bSHarald Geyer dht11->dev = dev; 310091a121bSHarald Geyer 3115fbb0bc4SHarald Geyer ret = of_get_gpio(node, 0); 312091a121bSHarald Geyer if (ret < 0) 313091a121bSHarald Geyer return ret; 3145fbb0bc4SHarald Geyer dht11->gpio = ret; 315091a121bSHarald Geyer ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name); 316091a121bSHarald Geyer if (ret) 317091a121bSHarald Geyer return ret; 318091a121bSHarald Geyer 319091a121bSHarald Geyer dht11->irq = gpio_to_irq(dht11->gpio); 320091a121bSHarald Geyer if (dht11->irq < 0) { 321091a121bSHarald Geyer dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio); 322091a121bSHarald Geyer return -EINVAL; 323091a121bSHarald Geyer } 324091a121bSHarald Geyer 32517a2f46cSAbhilash Jindal dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1; 326091a121bSHarald Geyer dht11->num_edges = -1; 327091a121bSHarald Geyer 328091a121bSHarald Geyer platform_set_drvdata(pdev, iio); 329091a121bSHarald Geyer 330091a121bSHarald Geyer init_completion(&dht11->completion); 331004bc530SRichard Weinberger mutex_init(&dht11->lock); 332091a121bSHarald Geyer iio->name = pdev->name; 333091a121bSHarald Geyer iio->dev.parent = &pdev->dev; 334091a121bSHarald Geyer iio->info = &dht11_iio_info; 335091a121bSHarald Geyer iio->modes = INDIO_DIRECT_MODE; 336091a121bSHarald Geyer iio->channels = dht11_chan_spec; 337091a121bSHarald Geyer iio->num_channels = ARRAY_SIZE(dht11_chan_spec); 338091a121bSHarald Geyer 339091a121bSHarald Geyer return devm_iio_device_register(dev, iio); 340091a121bSHarald Geyer } 341091a121bSHarald Geyer 342091a121bSHarald Geyer static struct platform_driver dht11_driver = { 343091a121bSHarald Geyer .driver = { 344091a121bSHarald Geyer .name = DRIVER_NAME, 345091a121bSHarald Geyer .of_match_table = dht11_dt_ids, 346091a121bSHarald Geyer }, 347091a121bSHarald Geyer .probe = dht11_probe, 348091a121bSHarald Geyer }; 349091a121bSHarald Geyer 350091a121bSHarald Geyer module_platform_driver(dht11_driver); 351091a121bSHarald Geyer 352091a121bSHarald Geyer MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); 353091a121bSHarald Geyer MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); 354091a121bSHarald Geyer MODULE_LICENSE("GPL v2"); 355