/* * DHT11/DHT22 bit banging GPIO driver * * Copyright (c) Harald Geyer * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define DRIVER_NAME "dht11" #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ #define DHT11_EDGES_PREAMBLE 2 #define DHT11_BITS_PER_READ 40 /* * Note that when reading the sensor actually 84 edges are detected, but * since the last edge is not significant, we only store 83: */ #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \ DHT11_EDGES_PREAMBLE + 1) /* * Data transmission timing: * Data bits are encoded as pulse length (high time) on the data line. * 0-bit: 22-30uS -- typically 26uS (AM2302) * 1-bit: 68-75uS -- typically 70uS (AM2302) * The acutal timings also depend on the properties of the cable, with * longer cables typically making pulses shorter. * * Our decoding depends on the time resolution of the system: * timeres > 34uS ... don't know what a 1-tick pulse is * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks) * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is * timeres < 23uS ... no problem * * Luckily clocks in the 33-44kHz range are quite uncommon, so we can * support most systems if the threshold for decoding a pulse as 1-bit * is chosen carefully. If somebody really wants to support clocks around * 40kHz, where this driver is most unreliable, there are two options. * a) select an implementation using busy loop polling on those systems * b) use the checksum to do some probabilistic decoding */ #define DHT11_START_TRANSMISSION_MIN 18000 /* us */ #define DHT11_START_TRANSMISSION_MAX 20000 /* us */ #define DHT11_MIN_TIMERES 34000 /* ns */ #define DHT11_THRESHOLD 49000 /* ns */ #define DHT11_AMBIG_LOW 23000 /* ns */ #define DHT11_AMBIG_HIGH 30000 /* ns */ struct dht11 { struct device *dev; int gpio; int irq; struct completion completion; /* The iio sysfs interface doesn't prevent concurrent reads: */ struct mutex lock; s64 timestamp; int temperature; int humidity; /* num_edges: -1 means "no transmission in progress" */ int num_edges; struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; }; #ifdef CONFIG_DYNAMIC_DEBUG /* * dht11_edges_print: show the data as actually received by the * driver. */ static void dht11_edges_print(struct dht11 *dht11) { int i; dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges); for (i = 1; i < dht11->num_edges; ++i) { dev_dbg(dht11->dev, "%d: %lld ns %s\n", i, dht11->edges[i].ts - dht11->edges[i - 1].ts, dht11->edges[i - 1].value ? "high" : "low"); } } #endif /* CONFIG_DYNAMIC_DEBUG */ static unsigned char dht11_decode_byte(char *bits) { unsigned char ret = 0; int i; for (i = 0; i < 8; ++i) { ret <<= 1; if (bits[i]) ++ret; } return ret; } static int dht11_decode(struct dht11 *dht11, int offset) { int i, t; char bits[DHT11_BITS_PER_READ]; unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; for (i = 0; i < DHT11_BITS_PER_READ; ++i) { t = dht11->edges[offset + 2 * i + 2].ts - dht11->edges[offset + 2 * i + 1].ts; if (!dht11->edges[offset + 2 * i + 1].value) { dev_dbg(dht11->dev, "lost synchronisation at edge %d\n", offset + 2 * i + 1); return -EIO; } bits[i] = t > DHT11_THRESHOLD; } hum_int = dht11_decode_byte(bits); hum_dec = dht11_decode_byte(&bits[8]); temp_int = dht11_decode_byte(&bits[16]); temp_dec = dht11_decode_byte(&bits[24]); checksum = dht11_decode_byte(&bits[32]); if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) { dev_dbg(dht11->dev, "invalid checksum\n"); return -EIO; } dht11->timestamp = ktime_get_boot_ns(); if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */ dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * ((temp_int & 0x80) ? -100 : 100); dht11->humidity = ((hum_int << 8) + hum_dec) * 100; } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ dht11->temperature = temp_int * 1000; dht11->humidity = hum_int * 1000; } else { dev_err(dht11->dev, "Don't know how to decode data: %d %d %d %d\n", hum_int, hum_dec, temp_int, temp_dec); return -EIO; } return 0; } /* * IRQ handler called on GPIO edges */ static irqreturn_t dht11_handle_irq(int irq, void *data) { struct iio_dev *iio = data; struct dht11 *dht11 = iio_priv(iio); /* TODO: Consider making the handler safe for IRQ sharing */ if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns(); dht11->edges[dht11->num_edges++].value = gpio_get_value(dht11->gpio); if (dht11->num_edges >= DHT11_EDGES_PER_READ) complete(&dht11->completion); } return IRQ_HANDLED; } static int dht11_read_raw(struct iio_dev *iio_dev, const struct iio_chan_spec *chan, int *val, int *val2, long m) { struct dht11 *dht11 = iio_priv(iio_dev); int ret, timeres, offset; mutex_lock(&dht11->lock); if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) { timeres = ktime_get_resolution_ns(); dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres); if (timeres > DHT11_MIN_TIMERES) { dev_err(dht11->dev, "timeresolution %dns too low\n", timeres); /* In theory a better clock could become available * at some point ... and there is no error code * that really fits better. */ ret = -EAGAIN; goto err; } if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH) dev_warn(dht11->dev, "timeresolution: %dns - decoding ambiguous\n", timeres); reinit_completion(&dht11->completion); dht11->num_edges = 0; ret = gpio_direction_output(dht11->gpio, 0); if (ret) goto err; usleep_range(DHT11_START_TRANSMISSION_MIN, DHT11_START_TRANSMISSION_MAX); ret = gpio_direction_input(dht11->gpio); if (ret) goto err; ret = request_irq(dht11->irq, dht11_handle_irq, IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, iio_dev->name, iio_dev); if (ret) goto err; ret = wait_for_completion_killable_timeout(&dht11->completion, HZ); free_irq(dht11->irq, iio_dev); #ifdef CONFIG_DYNAMIC_DEBUG dht11_edges_print(dht11); #endif if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { dev_err(dht11->dev, "Only %d signal edges detected\n", dht11->num_edges); ret = -ETIMEDOUT; } if (ret < 0) goto err; offset = DHT11_EDGES_PREAMBLE + dht11->num_edges - DHT11_EDGES_PER_READ; for (; offset >= 0; --offset) { ret = dht11_decode(dht11, offset); if (!ret) break; } if (ret) goto err; } ret = IIO_VAL_INT; if (chan->type == IIO_TEMP) *val = dht11->temperature; else if (chan->type == IIO_HUMIDITYRELATIVE) *val = dht11->humidity; else ret = -EINVAL; err: dht11->num_edges = -1; mutex_unlock(&dht11->lock); return ret; } static const struct iio_info dht11_iio_info = { .read_raw = dht11_read_raw, }; static const struct iio_chan_spec dht11_chan_spec[] = { { .type = IIO_TEMP, .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, { .type = IIO_HUMIDITYRELATIVE, .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } }; static const struct of_device_id dht11_dt_ids[] = { { .compatible = "dht11", }, { } }; MODULE_DEVICE_TABLE(of, dht11_dt_ids); static int dht11_probe(struct platform_device *pdev) { struct device *dev = &pdev->dev; struct device_node *node = dev->of_node; struct dht11 *dht11; struct iio_dev *iio; int ret; iio = devm_iio_device_alloc(dev, sizeof(*dht11)); if (!iio) { dev_err(dev, "Failed to allocate IIO device\n"); return -ENOMEM; } dht11 = iio_priv(iio); dht11->dev = dev; ret = of_get_gpio(node, 0); if (ret < 0) return ret; dht11->gpio = ret; ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name); if (ret) return ret; dht11->irq = gpio_to_irq(dht11->gpio); if (dht11->irq < 0) { dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio); return -EINVAL; } dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1; dht11->num_edges = -1; platform_set_drvdata(pdev, iio); init_completion(&dht11->completion); mutex_init(&dht11->lock); iio->name = pdev->name; iio->dev.parent = &pdev->dev; iio->info = &dht11_iio_info; iio->modes = INDIO_DIRECT_MODE; iio->channels = dht11_chan_spec; iio->num_channels = ARRAY_SIZE(dht11_chan_spec); return devm_iio_device_register(dev, iio); } static struct platform_driver dht11_driver = { .driver = { .name = DRIVER_NAME, .of_match_table = dht11_dt_ids, }, .probe = dht11_probe, }; module_platform_driver(dht11_driver); MODULE_AUTHOR("Harald Geyer "); MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); MODULE_LICENSE("GPL v2");