/* * 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 #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 (nano seconds) */ #define DHT11_START_TRANSMISSION 18 /* ms */ #define DHT11_SENSOR_RESPONSE 80000 #define DHT11_START_BIT 50000 #define DHT11_DATA_BIT_LOW 27000 #define DHT11_DATA_BIT_HIGH 70000 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]; }; static unsigned char dht11_decode_byte(int *timing, int threshold) { unsigned char ret = 0; int i; for (i = 0; i < 8; ++i) { ret <<= 1; if (timing[i] >= threshold) ++ret; } return ret; } static int dht11_decode(struct dht11 *dht11, int offset) { int i, t, timing[DHT11_BITS_PER_READ], threshold, timeres = DHT11_SENSOR_RESPONSE; unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; /* Calculate timestamp resolution */ for (i = 1; i < dht11->num_edges; ++i) { t = dht11->edges[i].ts - dht11->edges[i - 1].ts; if (t > 0 && t < timeres) timeres = t; } if (2 * timeres > DHT11_DATA_BIT_HIGH) { pr_err("dht11: timeresolution %d too bad for decoding\n", timeres); return -EIO; } threshold = DHT11_DATA_BIT_HIGH / timeres; if (DHT11_DATA_BIT_LOW / timeres + 1 >= threshold) pr_err("dht11: WARNING: decoding ambiguous\n"); /* scale down with timeres and check validity */ 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) return -EIO; /* lost synchronisation */ timing[i] = t / timeres; } hum_int = dht11_decode_byte(timing, threshold); hum_dec = dht11_decode_byte(&timing[8], threshold); temp_int = dht11_decode_byte(&timing[16], threshold); temp_dec = dht11_decode_byte(&timing[24], threshold); checksum = dht11_decode_byte(&timing[32], threshold); if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) return -EIO; dht11->timestamp = iio_get_time_ns(); if (hum_int < 20) { /* DHT22 */ 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 = iio_get_time_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; mutex_lock(&dht11->lock); if (dht11->timestamp + DHT11_DATA_VALID_TIME < iio_get_time_ns()) { reinit_completion(&dht11->completion); dht11->num_edges = 0; ret = gpio_direction_output(dht11->gpio, 0); if (ret) goto err; msleep(DHT11_START_TRANSMISSION); 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); if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { dev_err(&iio_dev->dev, "Only %d signal edges detected\n", dht11->num_edges); ret = -ETIMEDOUT; } if (ret < 0) goto err; ret = dht11_decode(dht11, dht11->num_edges == DHT11_EDGES_PER_READ ? DHT11_EDGES_PREAMBLE : DHT11_EDGES_PREAMBLE - 2); 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 = { .driver_module = THIS_MODULE, .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 = iio_get_time_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");