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1// SPDX-License-Identifier: GPL-2.0-or-later2/*3 * DHT11/DHT22 bit banging GPIO driver4 *5 * Copyright (c) Harald Geyer <harald@ccbib.org>6 */7 8#include <linux/err.h>9#include <linux/interrupt.h>10#include <linux/device.h>11#include <linux/kernel.h>12#include <linux/printk.h>13#include <linux/slab.h>14#include <linux/sysfs.h>15#include <linux/io.h>16#include <linux/mod_devicetable.h>17#include <linux/module.h>18#include <linux/platform_device.h>19#include <linux/wait.h>20#include <linux/bitops.h>21#include <linux/completion.h>22#include <linux/mutex.h>23#include <linux/delay.h>24#include <linux/gpio/consumer.h>25#include <linux/timekeeping.h>26 27#include <linux/iio/iio.h>28 29#define DRIVER_NAME "dht11"30 31#define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */32 33#define DHT11_EDGES_PREAMBLE 234#define DHT11_BITS_PER_READ 4035/*36 * Note that when reading the sensor actually 84 edges are detected, but37 * since the last edge is not significant, we only store 83:38 */39#define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \40 DHT11_EDGES_PREAMBLE + 1)41 42/*43 * Data transmission timing:44 * Data bits are encoded as pulse length (high time) on the data line.45 * 0-bit: 22-30uS -- typically 26uS (AM2302)46 * 1-bit: 68-75uS -- typically 70uS (AM2302)47 * The acutal timings also depend on the properties of the cable, with48 * longer cables typically making pulses shorter.49 *50 * Our decoding depends on the time resolution of the system:51 * timeres > 34uS ... don't know what a 1-tick pulse is52 * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks)53 * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is54 * timeres < 23uS ... no problem55 *56 * Luckily clocks in the 33-44kHz range are quite uncommon, so we can57 * support most systems if the threshold for decoding a pulse as 1-bit58 * is chosen carefully. If somebody really wants to support clocks around59 * 40kHz, where this driver is most unreliable, there are two options.60 * a) select an implementation using busy loop polling on those systems61 * b) use the checksum to do some probabilistic decoding62 */63#define DHT11_START_TRANSMISSION_MIN 18000 /* us */64#define DHT11_START_TRANSMISSION_MAX 20000 /* us */65#define DHT11_MIN_TIMERES 34000 /* ns */66#define DHT11_THRESHOLD 49000 /* ns */67#define DHT11_AMBIG_LOW 23000 /* ns */68#define DHT11_AMBIG_HIGH 30000 /* ns */69 70struct dht11 {71 struct device *dev;72 73 struct gpio_desc *gpiod;74 int irq;75 76 struct completion completion;77 /* The iio sysfs interface doesn't prevent concurrent reads: */78 struct mutex lock;79 80 s64 timestamp;81 int temperature;82 int humidity;83 84 /* num_edges: -1 means "no transmission in progress" */85 int num_edges;86 struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ];87};88 89#ifdef CONFIG_DYNAMIC_DEBUG90/*91 * dht11_edges_print: show the data as actually received by the92 * driver.93 */94static void dht11_edges_print(struct dht11 *dht11)95{96 int i;97 98 dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);99 for (i = 1; i < dht11->num_edges; ++i) {100 dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,101 dht11->edges[i].ts - dht11->edges[i - 1].ts,102 dht11->edges[i - 1].value ? "high" : "low");103 }104}105#endif /* CONFIG_DYNAMIC_DEBUG */106 107static unsigned char dht11_decode_byte(char *bits)108{109 unsigned char ret = 0;110 int i;111 112 for (i = 0; i < 8; ++i) {113 ret <<= 1;114 if (bits[i])115 ++ret;116 }117 118 return ret;119}120 121static int dht11_decode(struct dht11 *dht11, int offset)122{123 int i, t;124 char bits[DHT11_BITS_PER_READ];125 unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;126 127 for (i = 0; i < DHT11_BITS_PER_READ; ++i) {128 t = dht11->edges[offset + 2 * i + 2].ts -129 dht11->edges[offset + 2 * i + 1].ts;130 if (!dht11->edges[offset + 2 * i + 1].value) {131 dev_dbg(dht11->dev,132 "lost synchronisation at edge %d\n",133 offset + 2 * i + 1);134 return -EIO;135 }136 bits[i] = t > DHT11_THRESHOLD;137 }138 139 hum_int = dht11_decode_byte(bits);140 hum_dec = dht11_decode_byte(&bits[8]);141 temp_int = dht11_decode_byte(&bits[16]);142 temp_dec = dht11_decode_byte(&bits[24]);143 checksum = dht11_decode_byte(&bits[32]);144 145 if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {146 dev_dbg(dht11->dev, "invalid checksum\n");147 return -EIO;148 }149 150 dht11->timestamp = ktime_get_boottime_ns();151 if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */152 dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *153 ((temp_int & 0x80) ? -100 : 100);154 dht11->humidity = ((hum_int << 8) + hum_dec) * 100;155 } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */156 dht11->temperature = temp_int * 1000;157 dht11->humidity = hum_int * 1000;158 } else {159 dev_err(dht11->dev,160 "Don't know how to decode data: %d %d %d %d\n",161 hum_int, hum_dec, temp_int, temp_dec);162 return -EIO;163 }164 165 return 0;166}167 168/*169 * IRQ handler called on GPIO edges170 */171static irqreturn_t dht11_handle_irq(int irq, void *data)172{173 struct iio_dev *iio = data;174 struct dht11 *dht11 = iio_priv(iio);175 176 if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {177 dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns();178 dht11->edges[dht11->num_edges++].value =179 gpiod_get_value(dht11->gpiod);180 181 if (dht11->num_edges >= DHT11_EDGES_PER_READ)182 complete(&dht11->completion);183 }184 185 return IRQ_HANDLED;186}187 188static int dht11_read_raw(struct iio_dev *iio_dev,189 const struct iio_chan_spec *chan,190 int *val, int *val2, long m)191{192 struct dht11 *dht11 = iio_priv(iio_dev);193 int ret, timeres, offset;194 195 mutex_lock(&dht11->lock);196 if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boottime_ns()) {197 timeres = ktime_get_resolution_ns();198 dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);199 if (timeres > DHT11_MIN_TIMERES) {200 dev_err(dht11->dev, "timeresolution %dns too low\n",201 timeres);202 /* In theory a better clock could become available203 * at some point ... and there is no error code204 * that really fits better.205 */206 ret = -EAGAIN;207 goto err;208 }209 if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)210 dev_warn(dht11->dev,211 "timeresolution: %dns - decoding ambiguous\n",212 timeres);213 214 reinit_completion(&dht11->completion);215 216 dht11->num_edges = 0;217 ret = gpiod_direction_output(dht11->gpiod, 0);218 if (ret)219 goto err;220 usleep_range(DHT11_START_TRANSMISSION_MIN,221 DHT11_START_TRANSMISSION_MAX);222 ret = gpiod_direction_input(dht11->gpiod);223 if (ret)224 goto err;225 226 ret = request_irq(dht11->irq, dht11_handle_irq,227 IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,228 iio_dev->name, iio_dev);229 if (ret)230 goto err;231 232 ret = wait_for_completion_killable_timeout(&dht11->completion,233 HZ);234 235 free_irq(dht11->irq, iio_dev);236 237#ifdef CONFIG_DYNAMIC_DEBUG238 dht11_edges_print(dht11);239#endif240 241 if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {242 dev_err(dht11->dev, "Only %d signal edges detected\n",243 dht11->num_edges);244 ret = -ETIMEDOUT;245 }246 if (ret < 0)247 goto err;248 249 offset = DHT11_EDGES_PREAMBLE +250 dht11->num_edges - DHT11_EDGES_PER_READ;251 for (; offset >= 0; --offset) {252 ret = dht11_decode(dht11, offset);253 if (!ret)254 break;255 }256 257 if (ret)258 goto err;259 }260 261 ret = IIO_VAL_INT;262 if (chan->type == IIO_TEMP)263 *val = dht11->temperature;264 else if (chan->type == IIO_HUMIDITYRELATIVE)265 *val = dht11->humidity;266 else267 ret = -EINVAL;268err:269 dht11->num_edges = -1;270 mutex_unlock(&dht11->lock);271 return ret;272}273 274static const struct iio_info dht11_iio_info = {275 .read_raw = dht11_read_raw,276};277 278static const struct iio_chan_spec dht11_chan_spec[] = {279 { .type = IIO_TEMP,280 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },281 { .type = IIO_HUMIDITYRELATIVE,282 .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }283};284 285static const struct of_device_id dht11_dt_ids[] = {286 { .compatible = "dht11", },287 { }288};289MODULE_DEVICE_TABLE(of, dht11_dt_ids);290 291static int dht11_probe(struct platform_device *pdev)292{293 struct device *dev = &pdev->dev;294 struct dht11 *dht11;295 struct iio_dev *iio;296 297 iio = devm_iio_device_alloc(dev, sizeof(*dht11));298 if (!iio) {299 dev_err(dev, "Failed to allocate IIO device\n");300 return -ENOMEM;301 }302 303 dht11 = iio_priv(iio);304 dht11->dev = dev;305 dht11->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN);306 if (IS_ERR(dht11->gpiod))307 return PTR_ERR(dht11->gpiod);308 309 dht11->irq = gpiod_to_irq(dht11->gpiod);310 if (dht11->irq < 0) {311 dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod));312 return -EINVAL;313 }314 315 dht11->timestamp = ktime_get_boottime_ns() - DHT11_DATA_VALID_TIME - 1;316 dht11->num_edges = -1;317 318 platform_set_drvdata(pdev, iio);319 320 init_completion(&dht11->completion);321 mutex_init(&dht11->lock);322 iio->name = pdev->name;323 iio->info = &dht11_iio_info;324 iio->modes = INDIO_DIRECT_MODE;325 iio->channels = dht11_chan_spec;326 iio->num_channels = ARRAY_SIZE(dht11_chan_spec);327 328 return devm_iio_device_register(dev, iio);329}330 331static struct platform_driver dht11_driver = {332 .driver = {333 .name = DRIVER_NAME,334 .of_match_table = dht11_dt_ids,335 },336 .probe = dht11_probe,337};338 339module_platform_driver(dht11_driver);340 341MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");342MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");343MODULE_LICENSE("GPL v2");344