xref: /openbmc/linux/drivers/iio/humidity/dht11.c (revision b34e08d5)
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");
295