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091a121b HG |
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/delay.h> | |
33 | #include <linux/gpio.h> | |
34 | #include <linux/of_gpio.h> | |
35 | ||
36 | #include <linux/iio/iio.h> | |
37 | ||
38 | #define DRIVER_NAME "dht11" | |
39 | ||
40 | #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ | |
41 | ||
42 | #define DHT11_EDGES_PREAMBLE 4 | |
43 | #define DHT11_BITS_PER_READ 40 | |
44 | #define DHT11_EDGES_PER_READ (2*DHT11_BITS_PER_READ + DHT11_EDGES_PREAMBLE + 1) | |
45 | ||
46 | /* Data transmission timing (nano seconds) */ | |
47 | #define DHT11_START_TRANSMISSION 18 /* ms */ | |
48 | #define DHT11_SENSOR_RESPONSE 80000 | |
49 | #define DHT11_START_BIT 50000 | |
50 | #define DHT11_DATA_BIT_LOW 27000 | |
51 | #define DHT11_DATA_BIT_HIGH 70000 | |
52 | ||
53 | struct dht11 { | |
54 | struct device *dev; | |
55 | ||
56 | int gpio; | |
57 | int irq; | |
58 | ||
59 | struct completion completion; | |
60 | ||
61 | s64 timestamp; | |
62 | int temperature; | |
63 | int humidity; | |
64 | ||
65 | /* num_edges: -1 means "no transmission in progress" */ | |
66 | int num_edges; | |
67 | struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; | |
68 | }; | |
69 | ||
70 | static unsigned char dht11_decode_byte(int *timing, int threshold) | |
71 | { | |
72 | unsigned char ret = 0; | |
73 | int i; | |
74 | ||
75 | for (i = 0; i < 8; ++i) { | |
76 | ret <<= 1; | |
77 | if (timing[i] >= threshold) | |
78 | ++ret; | |
79 | } | |
80 | ||
81 | return ret; | |
82 | } | |
83 | ||
84 | static int dht11_decode(struct dht11 *dht11, int offset) | |
85 | { | |
86 | int i, t, timing[DHT11_BITS_PER_READ], threshold, | |
87 | timeres = DHT11_SENSOR_RESPONSE; | |
88 | unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; | |
89 | ||
90 | /* Calculate timestamp resolution */ | |
91 | for (i = 0; i < dht11->num_edges; ++i) { | |
92 | t = dht11->edges[i].ts - dht11->edges[i-1].ts; | |
93 | if (t > 0 && t < timeres) | |
94 | timeres = t; | |
95 | } | |
96 | if (2*timeres > DHT11_DATA_BIT_HIGH) { | |
97 | pr_err("dht11: timeresolution %d too bad for decoding\n", | |
98 | timeres); | |
99 | return -EIO; | |
100 | } | |
101 | threshold = DHT11_DATA_BIT_HIGH / timeres; | |
102 | if (DHT11_DATA_BIT_LOW/timeres + 1 >= threshold) | |
103 | pr_err("dht11: WARNING: decoding ambiguous\n"); | |
104 | ||
105 | /* scale down with timeres and check validity */ | |
106 | for (i = 0; i < DHT11_BITS_PER_READ; ++i) { | |
107 | t = dht11->edges[offset + 2*i + 2].ts - | |
108 | dht11->edges[offset + 2*i + 1].ts; | |
109 | if (!dht11->edges[offset + 2*i + 1].value) | |
110 | return -EIO; /* lost synchronisation */ | |
111 | timing[i] = t / timeres; | |
112 | } | |
113 | ||
114 | hum_int = dht11_decode_byte(timing, threshold); | |
115 | hum_dec = dht11_decode_byte(&timing[8], threshold); | |
116 | temp_int = dht11_decode_byte(&timing[16], threshold); | |
117 | temp_dec = dht11_decode_byte(&timing[24], threshold); | |
118 | checksum = dht11_decode_byte(&timing[32], threshold); | |
119 | ||
120 | if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) | |
121 | return -EIO; | |
122 | ||
123 | dht11->timestamp = iio_get_time_ns(); | |
124 | if (hum_int < 20) { /* DHT22 */ | |
125 | dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * | |
126 | ((temp_int & 0x80) ? -100 : 100); | |
127 | dht11->humidity = ((hum_int << 8) + hum_dec) * 100; | |
128 | } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ | |
129 | dht11->temperature = temp_int * 1000; | |
130 | dht11->humidity = hum_int * 1000; | |
131 | } else { | |
132 | dev_err(dht11->dev, | |
133 | "Don't know how to decode data: %d %d %d %d\n", | |
134 | hum_int, hum_dec, temp_int, temp_dec); | |
135 | return -EIO; | |
136 | } | |
137 | ||
138 | return 0; | |
139 | } | |
140 | ||
141 | static int dht11_read_raw(struct iio_dev *iio_dev, | |
142 | const struct iio_chan_spec *chan, | |
143 | int *val, int *val2, long m) | |
144 | { | |
145 | struct dht11 *dht11 = iio_priv(iio_dev); | |
146 | int ret; | |
147 | ||
148 | if (dht11->timestamp + DHT11_DATA_VALID_TIME < iio_get_time_ns()) { | |
149 | reinit_completion(&dht11->completion); | |
150 | ||
151 | dht11->num_edges = 0; | |
152 | ret = gpio_direction_output(dht11->gpio, 0); | |
153 | if (ret) | |
154 | goto err; | |
155 | msleep(DHT11_START_TRANSMISSION); | |
156 | ret = gpio_direction_input(dht11->gpio); | |
157 | if (ret) | |
158 | goto err; | |
159 | ||
160 | ret = wait_for_completion_killable_timeout(&dht11->completion, | |
161 | HZ); | |
162 | if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { | |
163 | dev_err(&iio_dev->dev, | |
164 | "Only %d signal edges detected\n", | |
165 | dht11->num_edges); | |
166 | ret = -ETIMEDOUT; | |
167 | } | |
168 | if (ret < 0) | |
169 | goto err; | |
170 | ||
171 | ret = dht11_decode(dht11, | |
172 | dht11->num_edges == DHT11_EDGES_PER_READ ? | |
173 | DHT11_EDGES_PREAMBLE : | |
174 | DHT11_EDGES_PREAMBLE - 2); | |
175 | if (ret) | |
176 | goto err; | |
177 | } | |
178 | ||
179 | ret = IIO_VAL_INT; | |
180 | if (chan->type == IIO_TEMP) | |
181 | *val = dht11->temperature; | |
182 | else if (chan->type == IIO_HUMIDITYRELATIVE) | |
183 | *val = dht11->humidity; | |
184 | else | |
185 | ret = -EINVAL; | |
186 | err: | |
187 | dht11->num_edges = -1; | |
188 | return ret; | |
189 | } | |
190 | ||
191 | static const struct iio_info dht11_iio_info = { | |
192 | .driver_module = THIS_MODULE, | |
193 | .read_raw = dht11_read_raw, | |
194 | }; | |
195 | ||
196 | /* | |
197 | * IRQ handler called on GPIO edges | |
198 | */ | |
199 | static irqreturn_t dht11_handle_irq(int irq, void *data) | |
200 | { | |
201 | struct iio_dev *iio = data; | |
202 | struct dht11 *dht11 = iio_priv(iio); | |
203 | ||
204 | /* TODO: Consider making the handler safe for IRQ sharing */ | |
205 | if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { | |
206 | dht11->edges[dht11->num_edges].ts = iio_get_time_ns(); | |
207 | dht11->edges[dht11->num_edges++].value = | |
208 | gpio_get_value(dht11->gpio); | |
209 | ||
210 | if (dht11->num_edges >= DHT11_EDGES_PER_READ) | |
211 | complete(&dht11->completion); | |
212 | } | |
213 | ||
214 | return IRQ_HANDLED; | |
215 | } | |
216 | ||
217 | static const struct iio_chan_spec dht11_chan_spec[] = { | |
218 | { .type = IIO_TEMP, | |
219 | .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, | |
220 | { .type = IIO_HUMIDITYRELATIVE, | |
221 | .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } | |
222 | }; | |
223 | ||
224 | static const struct of_device_id dht11_dt_ids[] = { | |
225 | { .compatible = "dht11", }, | |
226 | { } | |
227 | }; | |
228 | MODULE_DEVICE_TABLE(of, dht11_dt_ids); | |
229 | ||
230 | static int dht11_probe(struct platform_device *pdev) | |
231 | { | |
232 | struct device *dev = &pdev->dev; | |
233 | struct device_node *node = dev->of_node; | |
234 | struct dht11 *dht11; | |
235 | struct iio_dev *iio; | |
236 | int ret; | |
237 | ||
238 | iio = devm_iio_device_alloc(dev, sizeof(*dht11)); | |
239 | if (!iio) { | |
240 | dev_err(dev, "Failed to allocate IIO device\n"); | |
241 | return -ENOMEM; | |
242 | } | |
243 | ||
244 | dht11 = iio_priv(iio); | |
245 | dht11->dev = dev; | |
246 | ||
247 | dht11->gpio = ret = of_get_gpio(node, 0); | |
248 | if (ret < 0) | |
249 | return ret; | |
250 | ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name); | |
251 | if (ret) | |
252 | return ret; | |
253 | ||
254 | dht11->irq = gpio_to_irq(dht11->gpio); | |
255 | if (dht11->irq < 0) { | |
256 | dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio); | |
257 | return -EINVAL; | |
258 | } | |
259 | ret = devm_request_irq(dev, dht11->irq, dht11_handle_irq, | |
260 | IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, | |
261 | pdev->name, iio); | |
262 | if (ret) | |
263 | return ret; | |
264 | ||
265 | dht11->timestamp = iio_get_time_ns() - DHT11_DATA_VALID_TIME - 1; | |
266 | dht11->num_edges = -1; | |
267 | ||
268 | platform_set_drvdata(pdev, iio); | |
269 | ||
270 | init_completion(&dht11->completion); | |
271 | iio->name = pdev->name; | |
272 | iio->dev.parent = &pdev->dev; | |
273 | iio->info = &dht11_iio_info; | |
274 | iio->modes = INDIO_DIRECT_MODE; | |
275 | iio->channels = dht11_chan_spec; | |
276 | iio->num_channels = ARRAY_SIZE(dht11_chan_spec); | |
277 | ||
278 | return devm_iio_device_register(dev, iio); | |
279 | } | |
280 | ||
281 | static struct platform_driver dht11_driver = { | |
282 | .driver = { | |
283 | .name = DRIVER_NAME, | |
284 | .owner = THIS_MODULE, | |
285 | .of_match_table = dht11_dt_ids, | |
286 | }, | |
287 | .probe = dht11_probe, | |
288 | }; | |
289 | ||
290 | module_platform_driver(dht11_driver); | |
291 | ||
292 | MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); | |
293 | MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); | |
294 | MODULE_LICENSE("GPL v2"); |