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
|
/*
* 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/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 (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;
/* 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];
};
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 timeres)
{
int i, t, timing[DHT11_BITS_PER_READ], threshold;
unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
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 = ktime_get_real_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 = ktime_get_real_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;
mutex_lock(&dht11->lock);
if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_real_ns()) {
timeres = ktime_get_resolution_ns();
if (DHT11_DATA_BIT_HIGH < 2 * 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;
}
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,
timeres);
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;
ret = of_get_gpio(node, 0);
if (ret < 0)
return ret;
dht11->gpio
|