--- /dev/null
+/*
+ * 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/mutex.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 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;
+ 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;
+
+ 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;
+ }
+
+ 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 <harald@ccbib.org>");
+MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
+MODULE_LICENSE("GPL v2");
Code Review / kvmfornfv.git / blobdiff