diff options
Diffstat (limited to 'drivers/iio/humidity/dht11.c')
| -rw-r--r-- | drivers/iio/humidity/dht11.c | 294 |
1 files changed, 294 insertions, 0 deletions
diff --git a/drivers/iio/humidity/dht11.c b/drivers/iio/humidity/dht11.c new file mode 100644 index 000000000000..d8771f546bf2 --- /dev/null +++ b/drivers/iio/humidity/dht11.c @@ -0,0 +1,294 @@ +/* + * DHT11/DHT22 bit banging GPIO driver + * + * Copyright (c) Harald Geyer <harald@ccbib.org> + * + * 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 <linux/err.h> +#include <linux/interrupt.h> +#include <linux/device.h> +#include <linux/kernel.h> +#include <linux/printk.h> +#include <linux/slab.h> +#include <linux/of.h> +#include <linux/of_device.h> +#include <linux/sysfs.h> +#include <linux/io.h> +#include <linux/module.h> +#include <linux/platform_device.h> +#include <linux/wait.h> +#include <linux/bitops.h> +#include <linux/completion.h> +#include <linux/delay.h> +#include <linux/gpio.h> +#include <linux/of_gpio.h> + +#include <linux/iio/iio.h> + +#define DRIVER_NAME "dht11" + +#define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ + +#define DHT11_EDGES_PREAMBLE 4 +#define DHT11_BITS_PER_READ 40 +#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; + + 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 = 0; 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; +} + +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; + + 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 = wait_for_completion_killable_timeout(&dht11->completion, + HZ); + 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; + return ret; +} + +static const struct iio_info dht11_iio_info = { + .driver_module = THIS_MODULE, + .read_raw = dht11_read_raw, +}; + +/* + * 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 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; + + dht11->gpio = ret = of_get_gpio(node, 0); + if (ret < 0) + return 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; + } + ret = devm_request_irq(dev, dht11->irq, dht11_handle_irq, + IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, + pdev->name, iio); + if (ret) + return ret; + + dht11->timestamp = iio_get_time_ns() - DHT11_DATA_VALID_TIME - 1; + dht11->num_edges = -1; + + platform_set_drvdata(pdev, iio); + + init_completion(&dht11->completion); + 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, + .owner = THIS_MODULE, + .of_match_table = dht11_dt_ids, + }, + .probe = dht11_probe, +}; + +module_platform_driver(dht11_driver); + +MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); +MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); +MODULE_LICENSE("GPL v2"); |