1/*
2 * DHT11/DHT22 bit banging GPIO driver
3 *
4 * Copyright (c) Harald Geyer <harald@ccbib.org>
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 */
16
17#include <linux/err.h>
18#include <linux/interrupt.h>
19#include <linux/device.h>
20#include <linux/kernel.h>
21#include <linux/printk.h>
22#include <linux/slab.h>
23#include <linux/of.h>
24#include <linux/of_device.h>
25#include <linux/sysfs.h>
26#include <linux/io.h>
27#include <linux/module.h>
28#include <linux/platform_device.h>
29#include <linux/wait.h>
30#include <linux/bitops.h>
31#include <linux/completion.h>
32#include <linux/mutex.h>
33#include <linux/delay.h>
34#include <linux/gpio.h>
35#include <linux/of_gpio.h>
36
37#include <linux/iio/iio.h>
38
39#define DRIVER_NAME	"dht11"
40
41#define DHT11_DATA_VALID_TIME	2000000000  /* 2s in ns */
42
43#define DHT11_EDGES_PREAMBLE 2
44#define DHT11_BITS_PER_READ 40
45/*
46 * Note that when reading the sensor actually 84 edges are detected, but
47 * since the last edge is not significant, we only store 83:
48 */
49#define DHT11_EDGES_PER_READ (2*DHT11_BITS_PER_READ + DHT11_EDGES_PREAMBLE + 1)
50
51/* Data transmission timing (nano seconds) */
52#define DHT11_START_TRANSMISSION	18  /* ms */
53#define DHT11_SENSOR_RESPONSE	80000
54#define DHT11_START_BIT		50000
55#define DHT11_DATA_BIT_LOW	27000
56#define DHT11_DATA_BIT_HIGH	70000
57
58struct dht11 {
59	struct device			*dev;
60
61	int				gpio;
62	int				irq;
63
64	struct completion		completion;
65	struct mutex			lock;
66
67	s64				timestamp;
68	int				temperature;
69	int				humidity;
70
71	/* num_edges: -1 means "no transmission in progress" */
72	int				num_edges;
73	struct {s64 ts; int value; }	edges[DHT11_EDGES_PER_READ];
74};
75
76static unsigned char dht11_decode_byte(int *timing, int threshold)
77{
78	unsigned char ret = 0;
79	int i;
80
81	for (i = 0; i < 8; ++i) {
82		ret <<= 1;
83		if (timing[i] >= threshold)
84			++ret;
85	}
86
87	return ret;
88}
89
90static int dht11_decode(struct dht11 *dht11, int offset)
91{
92	int i, t, timing[DHT11_BITS_PER_READ], threshold,
93		timeres = DHT11_SENSOR_RESPONSE;
94	unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
95
96	/* Calculate timestamp resolution */
97	for (i = 1; i < dht11->num_edges; ++i) {
98		t = dht11->edges[i].ts - dht11->edges[i-1].ts;
99		if (t > 0 && t < timeres)
100			timeres = t;
101	}
102	if (2*timeres > DHT11_DATA_BIT_HIGH) {
103		pr_err("dht11: timeresolution %d too bad for decoding\n",
104			timeres);
105		return -EIO;
106	}
107	threshold = DHT11_DATA_BIT_HIGH / timeres;
108	if (DHT11_DATA_BIT_LOW/timeres + 1 >= threshold)
109		pr_err("dht11: WARNING: decoding ambiguous\n");
110
111	/* scale down with timeres and check validity */
112	for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
113		t = dht11->edges[offset + 2*i + 2].ts -
114			dht11->edges[offset + 2*i + 1].ts;
115		if (!dht11->edges[offset + 2*i + 1].value)
116			return -EIO;  /* lost synchronisation */
117		timing[i] = t / timeres;
118	}
119
120	hum_int = dht11_decode_byte(timing, threshold);
121	hum_dec = dht11_decode_byte(&timing[8], threshold);
122	temp_int = dht11_decode_byte(&timing[16], threshold);
123	temp_dec = dht11_decode_byte(&timing[24], threshold);
124	checksum = dht11_decode_byte(&timing[32], threshold);
125
126	if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum)
127		return -EIO;
128
129	dht11->timestamp = iio_get_time_ns();
130	if (hum_int < 20) {  /* DHT22 */
131		dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
132					((temp_int & 0x80) ? -100 : 100);
133		dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
134	} else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
135		dht11->temperature = temp_int * 1000;
136		dht11->humidity = hum_int * 1000;
137	} else {
138		dev_err(dht11->dev,
139			"Don't know how to decode data: %d %d %d %d\n",
140			hum_int, hum_dec, temp_int, temp_dec);
141		return -EIO;
142	}
143
144	return 0;
145}
146
147/*
148 * IRQ handler called on GPIO edges
149 */
150static irqreturn_t dht11_handle_irq(int irq, void *data)
151{
152	struct iio_dev *iio = data;
153	struct dht11 *dht11 = iio_priv(iio);
154
155	/* TODO: Consider making the handler safe for IRQ sharing */
156	if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
157		dht11->edges[dht11->num_edges].ts = iio_get_time_ns();
158		dht11->edges[dht11->num_edges++].value =
159						gpio_get_value(dht11->gpio);
160
161		if (dht11->num_edges >= DHT11_EDGES_PER_READ)
162			complete(&dht11->completion);
163	}
164
165	return IRQ_HANDLED;
166}
167
168static int dht11_read_raw(struct iio_dev *iio_dev,
169			const struct iio_chan_spec *chan,
170			int *val, int *val2, long m)
171{
172	struct dht11 *dht11 = iio_priv(iio_dev);
173	int ret;
174
175	mutex_lock(&dht11->lock);
176	if (dht11->timestamp + DHT11_DATA_VALID_TIME < iio_get_time_ns()) {
177		reinit_completion(&dht11->completion);
178
179		dht11->num_edges = 0;
180		ret = gpio_direction_output(dht11->gpio, 0);
181		if (ret)
182			goto err;
183		msleep(DHT11_START_TRANSMISSION);
184		ret = gpio_direction_input(dht11->gpio);
185		if (ret)
186			goto err;
187
188		ret = request_irq(dht11->irq, dht11_handle_irq,
189				  IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
190				  iio_dev->name, iio_dev);
191		if (ret)
192			goto err;
193
194		ret = wait_for_completion_killable_timeout(&dht11->completion,
195								 HZ);
196
197		free_irq(dht11->irq, iio_dev);
198
199		if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
200			dev_err(&iio_dev->dev,
201					"Only %d signal edges detected\n",
202					dht11->num_edges);
203			ret = -ETIMEDOUT;
204		}
205		if (ret < 0)
206			goto err;
207
208		ret = dht11_decode(dht11,
209				dht11->num_edges == DHT11_EDGES_PER_READ ?
210					DHT11_EDGES_PREAMBLE :
211					DHT11_EDGES_PREAMBLE - 2);
212		if (ret)
213			goto err;
214	}
215
216	ret = IIO_VAL_INT;
217	if (chan->type == IIO_TEMP)
218		*val = dht11->temperature;
219	else if (chan->type == IIO_HUMIDITYRELATIVE)
220		*val = dht11->humidity;
221	else
222		ret = -EINVAL;
223err:
224	dht11->num_edges = -1;
225	mutex_unlock(&dht11->lock);
226	return ret;
227}
228
229static const struct iio_info dht11_iio_info = {
230	.driver_module		= THIS_MODULE,
231	.read_raw		= dht11_read_raw,
232};
233
234static const struct iio_chan_spec dht11_chan_spec[] = {
235	{ .type = IIO_TEMP,
236		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
237	{ .type = IIO_HUMIDITYRELATIVE,
238		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
239};
240
241static const struct of_device_id dht11_dt_ids[] = {
242	{ .compatible = "dht11", },
243	{ }
244};
245MODULE_DEVICE_TABLE(of, dht11_dt_ids);
246
247static int dht11_probe(struct platform_device *pdev)
248{
249	struct device *dev = &pdev->dev;
250	struct device_node *node = dev->of_node;
251	struct dht11 *dht11;
252	struct iio_dev *iio;
253	int ret;
254
255	iio = devm_iio_device_alloc(dev, sizeof(*dht11));
256	if (!iio) {
257		dev_err(dev, "Failed to allocate IIO device\n");
258		return -ENOMEM;
259	}
260
261	dht11 = iio_priv(iio);
262	dht11->dev = dev;
263
264	dht11->gpio = ret = of_get_gpio(node, 0);
265	if (ret < 0)
266		return ret;
267	ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
268	if (ret)
269		return ret;
270
271	dht11->irq = gpio_to_irq(dht11->gpio);
272	if (dht11->irq < 0) {
273		dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
274		return -EINVAL;
275	}
276
277	dht11->timestamp = iio_get_time_ns() - DHT11_DATA_VALID_TIME - 1;
278	dht11->num_edges = -1;
279
280	platform_set_drvdata(pdev, iio);
281
282	init_completion(&dht11->completion);
283	mutex_init(&dht11->lock);
284	iio->name = pdev->name;
285	iio->dev.parent = &pdev->dev;
286	iio->info = &dht11_iio_info;
287	iio->modes = INDIO_DIRECT_MODE;
288	iio->channels = dht11_chan_spec;
289	iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
290
291	return devm_iio_device_register(dev, iio);
292}
293
294static struct platform_driver dht11_driver = {
295	.driver = {
296		.name	= DRIVER_NAME,
297		.of_match_table = dht11_dt_ids,
298	},
299	.probe  = dht11_probe,
300};
301
302module_platform_driver(dht11_driver);
303
304MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
305MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
306MODULE_LICENSE("GPL v2");
307