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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> | |
004bc530 | 32 | #include <linux/mutex.h> |
091a121b HG |
33 | #include <linux/delay.h> |
34 | #include <linux/gpio.h> | |
35 | #include <linux/of_gpio.h> | |
081d9740 | 36 | #include <linux/timekeeping.h> |
091a121b HG |
37 | |
38 | #include <linux/iio/iio.h> | |
39 | ||
40 | #define DRIVER_NAME "dht11" | |
41 | ||
42 | #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ | |
43 | ||
94e65519 | 44 | #define DHT11_EDGES_PREAMBLE 2 |
091a121b | 45 | #define DHT11_BITS_PER_READ 40 |
94e65519 RW |
46 | /* |
47 | * Note that when reading the sensor actually 84 edges are detected, but | |
48 | * since the last edge is not significant, we only store 83: | |
49 | */ | |
889c5e9b HG |
50 | #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \ |
51 | DHT11_EDGES_PREAMBLE + 1) | |
091a121b HG |
52 | |
53 | /* Data transmission timing (nano seconds) */ | |
54 | #define DHT11_START_TRANSMISSION 18 /* ms */ | |
55 | #define DHT11_SENSOR_RESPONSE 80000 | |
56 | #define DHT11_START_BIT 50000 | |
57 | #define DHT11_DATA_BIT_LOW 27000 | |
58 | #define DHT11_DATA_BIT_HIGH 70000 | |
59 | ||
60 | struct dht11 { | |
61 | struct device *dev; | |
62 | ||
63 | int gpio; | |
64 | int irq; | |
65 | ||
66 | struct completion completion; | |
a7126003 | 67 | /* The iio sysfs interface doesn't prevent concurrent reads: */ |
004bc530 | 68 | struct mutex lock; |
091a121b HG |
69 | |
70 | s64 timestamp; | |
71 | int temperature; | |
72 | int humidity; | |
73 | ||
74 | /* num_edges: -1 means "no transmission in progress" */ | |
75 | int num_edges; | |
76 | struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; | |
77 | }; | |
78 | ||
79 | static unsigned char dht11_decode_byte(int *timing, int threshold) | |
80 | { | |
81 | unsigned char ret = 0; | |
82 | int i; | |
83 | ||
84 | for (i = 0; i < 8; ++i) { | |
85 | ret <<= 1; | |
86 | if (timing[i] >= threshold) | |
87 | ++ret; | |
88 | } | |
89 | ||
90 | return ret; | |
91 | } | |
92 | ||
081d9740 | 93 | static int dht11_decode(struct dht11 *dht11, int offset, int timeres) |
091a121b | 94 | { |
081d9740 | 95 | int i, t, timing[DHT11_BITS_PER_READ], threshold; |
091a121b HG |
96 | unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; |
97 | ||
091a121b | 98 | threshold = DHT11_DATA_BIT_HIGH / timeres; |
889c5e9b | 99 | if (DHT11_DATA_BIT_LOW / timeres + 1 >= threshold) |
091a121b HG |
100 | pr_err("dht11: WARNING: decoding ambiguous\n"); |
101 | ||
102 | /* scale down with timeres and check validity */ | |
103 | for (i = 0; i < DHT11_BITS_PER_READ; ++i) { | |
889c5e9b HG |
104 | t = dht11->edges[offset + 2 * i + 2].ts - |
105 | dht11->edges[offset + 2 * i + 1].ts; | |
106 | if (!dht11->edges[offset + 2 * i + 1].value) | |
091a121b HG |
107 | return -EIO; /* lost synchronisation */ |
108 | timing[i] = t / timeres; | |
109 | } | |
110 | ||
111 | hum_int = dht11_decode_byte(timing, threshold); | |
112 | hum_dec = dht11_decode_byte(&timing[8], threshold); | |
113 | temp_int = dht11_decode_byte(&timing[16], threshold); | |
114 | temp_dec = dht11_decode_byte(&timing[24], threshold); | |
115 | checksum = dht11_decode_byte(&timing[32], threshold); | |
116 | ||
117 | if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) | |
118 | return -EIO; | |
119 | ||
17a2f46c | 120 | dht11->timestamp = ktime_get_boot_ns(); |
091a121b HG |
121 | if (hum_int < 20) { /* DHT22 */ |
122 | dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * | |
123 | ((temp_int & 0x80) ? -100 : 100); | |
124 | dht11->humidity = ((hum_int << 8) + hum_dec) * 100; | |
125 | } else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ | |
126 | dht11->temperature = temp_int * 1000; | |
127 | dht11->humidity = hum_int * 1000; | |
128 | } else { | |
129 | dev_err(dht11->dev, | |
130 | "Don't know how to decode data: %d %d %d %d\n", | |
131 | hum_int, hum_dec, temp_int, temp_dec); | |
132 | return -EIO; | |
133 | } | |
134 | ||
135 | return 0; | |
136 | } | |
137 | ||
94e65519 RW |
138 | /* |
139 | * IRQ handler called on GPIO edges | |
140 | */ | |
141 | static irqreturn_t dht11_handle_irq(int irq, void *data) | |
142 | { | |
143 | struct iio_dev *iio = data; | |
144 | struct dht11 *dht11 = iio_priv(iio); | |
145 | ||
146 | /* TODO: Consider making the handler safe for IRQ sharing */ | |
147 | if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { | |
17a2f46c | 148 | dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns(); |
94e65519 RW |
149 | dht11->edges[dht11->num_edges++].value = |
150 | gpio_get_value(dht11->gpio); | |
151 | ||
152 | if (dht11->num_edges >= DHT11_EDGES_PER_READ) | |
153 | complete(&dht11->completion); | |
154 | } | |
155 | ||
156 | return IRQ_HANDLED; | |
157 | } | |
158 | ||
091a121b | 159 | static int dht11_read_raw(struct iio_dev *iio_dev, |
889c5e9b | 160 | const struct iio_chan_spec *chan, |
091a121b HG |
161 | int *val, int *val2, long m) |
162 | { | |
163 | struct dht11 *dht11 = iio_priv(iio_dev); | |
081d9740 | 164 | int ret, timeres; |
091a121b | 165 | |
004bc530 | 166 | mutex_lock(&dht11->lock); |
17a2f46c | 167 | if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) { |
081d9740 HG |
168 | timeres = ktime_get_resolution_ns(); |
169 | if (DHT11_DATA_BIT_HIGH < 2 * timeres) { | |
170 | dev_err(dht11->dev, "timeresolution %dns too low\n", | |
171 | timeres); | |
172 | /* In theory a better clock could become available | |
173 | * at some point ... and there is no error code | |
174 | * that really fits better. | |
175 | */ | |
176 | ret = -EAGAIN; | |
177 | goto err; | |
178 | } | |
179 | ||
091a121b HG |
180 | reinit_completion(&dht11->completion); |
181 | ||
182 | dht11->num_edges = 0; | |
183 | ret = gpio_direction_output(dht11->gpio, 0); | |
184 | if (ret) | |
185 | goto err; | |
186 | msleep(DHT11_START_TRANSMISSION); | |
187 | ret = gpio_direction_input(dht11->gpio); | |
188 | if (ret) | |
189 | goto err; | |
190 | ||
94e65519 RW |
191 | ret = request_irq(dht11->irq, dht11_handle_irq, |
192 | IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, | |
193 | iio_dev->name, iio_dev); | |
194 | if (ret) | |
195 | goto err; | |
196 | ||
091a121b | 197 | ret = wait_for_completion_killable_timeout(&dht11->completion, |
889c5e9b | 198 | HZ); |
94e65519 RW |
199 | |
200 | free_irq(dht11->irq, iio_dev); | |
201 | ||
091a121b HG |
202 | if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { |
203 | dev_err(&iio_dev->dev, | |
889c5e9b | 204 | "Only %d signal edges detected\n", |
091a121b HG |
205 | dht11->num_edges); |
206 | ret = -ETIMEDOUT; | |
207 | } | |
208 | if (ret < 0) | |
209 | goto err; | |
210 | ||
211 | ret = dht11_decode(dht11, | |
889c5e9b | 212 | dht11->num_edges == DHT11_EDGES_PER_READ ? |
091a121b | 213 | DHT11_EDGES_PREAMBLE : |
081d9740 HG |
214 | DHT11_EDGES_PREAMBLE - 2, |
215 | timeres); | |
091a121b HG |
216 | if (ret) |
217 | goto err; | |
218 | } | |
219 | ||
220 | ret = IIO_VAL_INT; | |
221 | if (chan->type == IIO_TEMP) | |
222 | *val = dht11->temperature; | |
223 | else if (chan->type == IIO_HUMIDITYRELATIVE) | |
224 | *val = dht11->humidity; | |
225 | else | |
226 | ret = -EINVAL; | |
227 | err: | |
228 | dht11->num_edges = -1; | |
004bc530 | 229 | mutex_unlock(&dht11->lock); |
091a121b HG |
230 | return ret; |
231 | } | |
232 | ||
233 | static const struct iio_info dht11_iio_info = { | |
234 | .driver_module = THIS_MODULE, | |
235 | .read_raw = dht11_read_raw, | |
236 | }; | |
237 | ||
091a121b HG |
238 | static const struct iio_chan_spec dht11_chan_spec[] = { |
239 | { .type = IIO_TEMP, | |
240 | .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, | |
241 | { .type = IIO_HUMIDITYRELATIVE, | |
242 | .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } | |
243 | }; | |
244 | ||
245 | static const struct of_device_id dht11_dt_ids[] = { | |
246 | { .compatible = "dht11", }, | |
247 | { } | |
248 | }; | |
249 | MODULE_DEVICE_TABLE(of, dht11_dt_ids); | |
250 | ||
251 | static int dht11_probe(struct platform_device *pdev) | |
252 | { | |
253 | struct device *dev = &pdev->dev; | |
254 | struct device_node *node = dev->of_node; | |
255 | struct dht11 *dht11; | |
256 | struct iio_dev *iio; | |
257 | int ret; | |
258 | ||
259 | iio = devm_iio_device_alloc(dev, sizeof(*dht11)); | |
260 | if (!iio) { | |
261 | dev_err(dev, "Failed to allocate IIO device\n"); | |
262 | return -ENOMEM; | |
263 | } | |
264 | ||
265 | dht11 = iio_priv(iio); | |
266 | dht11->dev = dev; | |
267 | ||
5fbb0bc4 | 268 | ret = of_get_gpio(node, 0); |
091a121b HG |
269 | if (ret < 0) |
270 | return ret; | |
5fbb0bc4 | 271 | dht11->gpio = ret; |
091a121b HG |
272 | ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name); |
273 | if (ret) | |
274 | return ret; | |
275 | ||
276 | dht11->irq = gpio_to_irq(dht11->gpio); | |
277 | if (dht11->irq < 0) { | |
278 | dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio); | |
279 | return -EINVAL; | |
280 | } | |
091a121b | 281 | |
17a2f46c | 282 | dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1; |
091a121b HG |
283 | dht11->num_edges = -1; |
284 | ||
285 | platform_set_drvdata(pdev, iio); | |
286 | ||
287 | init_completion(&dht11->completion); | |
004bc530 | 288 | mutex_init(&dht11->lock); |
091a121b HG |
289 | iio->name = pdev->name; |
290 | iio->dev.parent = &pdev->dev; | |
291 | iio->info = &dht11_iio_info; | |
292 | iio->modes = INDIO_DIRECT_MODE; | |
293 | iio->channels = dht11_chan_spec; | |
294 | iio->num_channels = ARRAY_SIZE(dht11_chan_spec); | |
295 | ||
296 | return devm_iio_device_register(dev, iio); | |
297 | } | |
298 | ||
299 | static struct platform_driver dht11_driver = { | |
300 | .driver = { | |
301 | .name = DRIVER_NAME, | |
091a121b HG |
302 | .of_match_table = dht11_dt_ids, |
303 | }, | |
304 | .probe = dht11_probe, | |
305 | }; | |
306 | ||
307 | module_platform_driver(dht11_driver); | |
308 | ||
309 | MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>"); | |
310 | MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); | |
311 | MODULE_LICENSE("GPL v2"); |