iio: Add new driver dht11

This driver handles DHT11 and DHT22 sensors.

Signed-off-by: Harald Geyer <harald@ccbib.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

5 files changed, 316 insertions, 0 deletions

diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
index 90cf0cda50c4..a5ed88226276 100644
--- a/drivers/iio/Kconfig
+++ b/drivers/iio/Kconfig
@@ -65,6 +65,7 @@ source "drivers/iio/common/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"
diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
index bcf7e9e3b053..b3b50968b46b 100644
--- a/drivers/iio/Makefile
+++ b/drivers/iio/Makefile
@@ -18,6 +18,7 @@ obj-y += common/
 obj-y += dac/
 obj-y += gyro/
 obj-y += frequency/
+obj-y += humidity/
 obj-y += imu/
 obj-y += light/
 obj-y += magnetometer/
diff --git a/drivers/iio/humidity/Kconfig b/drivers/iio/humidity/Kconfig
new file mode 100644
index 000000000000..463c4d9da79e
--- /dev/null
+++ b/drivers/iio/humidity/Kconfig
@@ -0,0 +1,15 @@
+#
+# 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
diff --git a/drivers/iio/humidity/Makefile b/drivers/iio/humidity/Makefile
new file mode 100644
index 000000000000..d5d36c0c95f9
--- /dev/null
+++ b/drivers/iio/humidity/Makefile
@@ -0,0 +1,5 @@
+#
+# Makefile for IIO humidity sensor drivers
+#
+
+obj-$(CONFIG_DHT11) += dht11.o
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");