iio: Add new driver dht11

This driver handles DHT11 and DHT22 sensors.

Signed-off-by: Harald Geyer <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

Documentation/devicetree/bindings/iio/humidity/dht11.txt

···
+* DHT11 humidity/temperature sensor (and compatibles like DHT22)
+
+Required properties:
+  - compatible: Should be "dht11"
+  - gpios: Should specify the GPIO connected to the sensor's data
+    line, see "gpios property" in
+    Documentation/devicetree/bindings/gpio/gpio.txt.
+
+Example:
+
+humidity_sensor {
+	compatible = "dht11";
+	gpios = <&gpio0 6 0>;
+}

drivers/iio/Kconfig

···
 source "drivers/iio/dac/Kconfig"
 source "drivers/iio/frequency/Kconfig"
 source "drivers/iio/gyro/Kconfig"
+source "drivers/iio/humidity/Kconfig"
 source "drivers/iio/imu/Kconfig"
 source "drivers/iio/light/Kconfig"
 source "drivers/iio/magnetometer/Kconfig"

drivers/iio/Makefile

···
 obj-y += dac/
 obj-y += gyro/
 obj-y += frequency/
+obj-y += humidity/
 obj-y += imu/
 obj-y += light/
 obj-y += magnetometer/

drivers/iio/humidity/Kconfig

···
+#
+# humidity sensor drivers
+#
+menu "Humidity sensors"
+
+config DHT11
+	tristate "DHT11 (and compatible sensors) driver"
+	depends on GPIOLIB
+	help
+	  This driver supports reading data via a single interrupt
+	  generating GPIO line. Currently tested are DHT11 and DHT22.
+	  Other sensors should work as well as long as they speak the
+	  same protocol.
+
+endmenu

drivers/iio/humidity/Makefile

···
+#
+# Makefile for IIO humidity sensor drivers
+#
+
+obj-$(CONFIG_DHT11) += dht11.o

drivers/iio/humidity/dht11.c

···
+/*
+ * DHT11/DHT22 bit banging GPIO driver
+ *
+ * Copyright (c) Harald Geyer <[e-mail]>
+ *
+ * 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 <[e-mail]>");
+MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
+MODULE_LICENSE("GPL v2");