diff options
Diffstat (limited to 'drivers/iio/humidity/dht11.c')
| -rw-r--r-- | drivers/iio/humidity/dht11.c | 343 |
1 files changed, 343 insertions, 0 deletions
diff --git a/drivers/iio/humidity/dht11.c b/drivers/iio/humidity/dht11.c new file mode 100644 index 000000000..c97e25448 --- /dev/null +++ b/drivers/iio/humidity/dht11.c @@ -0,0 +1,343 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * DHT11/DHT22 bit banging GPIO driver + * + * Copyright (c) Harald Geyer <harald@ccbib.org> + */ + +#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/sysfs.h> +#include <linux/io.h> +#include <linux/mod_devicetable.h> +#include <linux/module.h> +#include <linux/platform_device.h> +#include <linux/wait.h> +#include <linux/bitops.h> +#include <linux/completion.h> +#include <linux/mutex.h> +#include <linux/delay.h> +#include <linux/gpio/consumer.h> +#include <linux/timekeeping.h> + +#include <linux/iio/iio.h> + +#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; + + struct gpio_desc *gpiod; + 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_boottime_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); + + if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { + dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns(); + dht11->edges[dht11->num_edges++].value = + gpiod_get_value(dht11->gpiod); + + 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_boottime_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 = gpiod_direction_output(dht11->gpiod, 0); + if (ret) + goto err; + usleep_range(DHT11_START_TRANSMISSION_MIN, + DHT11_START_TRANSMISSION_MAX); + ret = gpiod_direction_input(dht11->gpiod); + 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 dht11 *dht11; + struct iio_dev *iio; + + 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->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN); + if (IS_ERR(dht11->gpiod)) + return PTR_ERR(dht11->gpiod); + + dht11->irq = gpiod_to_irq(dht11->gpiod); + if (dht11->irq < 0) { + dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod)); + return -EINVAL; + } + + dht11->timestamp = ktime_get_boottime_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->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 <harald@ccbib.org>"); +MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); +MODULE_LICENSE("GPL v2"); |