summaryrefslogtreecommitdiff
path: root/drivers/iio/humidity/dht11.c
blob: c8159205c77de5e2963856a86ec7544e89cfd995 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
// 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/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/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;

	int				gpio;
	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_boot_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);

	/* 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 = ktime_get_boot_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, timeres, offset;

	mutex_lock(&dht11->lock);
	if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_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 = gpio_direction_output(dht11->gpio, 0);
		if (ret)
			goto err;
		usleep_range(DHT11_START_TRANSMISSION_MIN,
			     DHT11_START_TRANSMISSION_MAX);
		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);

#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 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;

	ret = of_get_gpio(node, 0);
	if (ret < 0)
		return ret;
	dht11->gpio = 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 = ktime_get_boot_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");