1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Sensirion SCD30 carbon dioxide sensor serial driver
4  *
5  * Copyright (c) 2020 Tomasz Duszynski <tomasz.duszynski@octakon.com>
6  */
7 #include <linux/crc16.h>
8 #include <linux/device.h>
9 #include <linux/errno.h>
10 #include <linux/iio/iio.h>
11 #include <linux/jiffies.h>
12 #include <linux/mod_devicetable.h>
13 #include <linux/module.h>
14 #include <linux/property.h>
15 #include <linux/serdev.h>
16 #include <linux/string.h>
17 #include <linux/types.h>
18 #include <asm/unaligned.h>
19 
20 #include "scd30.h"
21 
22 #define SCD30_SERDEV_ADDR 0x61
23 #define SCD30_SERDEV_WRITE 0x06
24 #define SCD30_SERDEV_READ 0x03
25 #define SCD30_SERDEV_MAX_BUF_SIZE 17
26 #define SCD30_SERDEV_RX_HEADER_SIZE 3
27 #define SCD30_SERDEV_CRC_SIZE 2
28 #define SCD30_SERDEV_TIMEOUT msecs_to_jiffies(200)
29 
30 struct scd30_serdev_priv {
31 	struct completion meas_ready;
32 	char *buf;
33 	int num_expected;
34 	int num;
35 };
36 
37 static u16 scd30_serdev_cmd_lookup_tbl[] = {
38 	[CMD_START_MEAS] = 0x0036,
39 	[CMD_STOP_MEAS] = 0x0037,
40 	[CMD_MEAS_INTERVAL] = 0x0025,
41 	[CMD_MEAS_READY] = 0x0027,
42 	[CMD_READ_MEAS] = 0x0028,
43 	[CMD_ASC] = 0x003a,
44 	[CMD_FRC] = 0x0039,
45 	[CMD_TEMP_OFFSET] = 0x003b,
46 	[CMD_FW_VERSION] = 0x0020,
47 	[CMD_RESET] = 0x0034,
48 };
49 
50 static u16 scd30_serdev_calc_crc(const char *buf, int size)
51 {
52 	return crc16(0xffff, buf, size);
53 }
54 
55 static int scd30_serdev_xfer(struct scd30_state *state, char *txbuf, int txsize,
56 			     char *rxbuf, int rxsize)
57 {
58 	struct serdev_device *serdev = to_serdev_device(state->dev);
59 	struct scd30_serdev_priv *priv = state->priv;
60 	int ret;
61 
62 	priv->buf = rxbuf;
63 	priv->num_expected = rxsize;
64 	priv->num = 0;
65 
66 	ret = serdev_device_write(serdev, txbuf, txsize, SCD30_SERDEV_TIMEOUT);
67 	if (ret < 0)
68 		return ret;
69 	if (ret != txsize)
70 		return -EIO;
71 
72 	ret = wait_for_completion_interruptible_timeout(&priv->meas_ready, SCD30_SERDEV_TIMEOUT);
73 	if (ret < 0)
74 		return ret;
75 	if (!ret)
76 		return -ETIMEDOUT;
77 
78 	return 0;
79 }
80 
81 static int scd30_serdev_command(struct scd30_state *state, enum scd30_cmd cmd, u16 arg,
82 				void *response, int size)
83 {
84 	/*
85 	 * Communication over serial line is based on modbus protocol (or rather
86 	 * its variation called modbus over serial to be precise). Upon
87 	 * receiving a request device should reply with response.
88 	 *
89 	 * Frame below represents a request message. Each field takes
90 	 * exactly one byte.
91 	 *
92 	 * +------+------+-----+-----+-------+-------+-----+-----+
93 	 * | dev  | op   | reg | reg | byte1 | byte0 | crc | crc |
94 	 * | addr | code | msb | lsb |       |       | lsb | msb |
95 	 * +------+------+-----+-----+-------+-------+-----+-----+
96 	 *
97 	 * The message device replies with depends on the 'op code' field from
98 	 * the request. In case it was set to SCD30_SERDEV_WRITE sensor should
99 	 * reply with unchanged request. Otherwise 'op code' was set to
100 	 * SCD30_SERDEV_READ and response looks like the one below. As with
101 	 * request, each field takes one byte.
102 	 *
103 	 * +------+------+--------+-------+-----+-------+-----+-----+
104 	 * | dev  | op   | num of | byte0 | ... | byteN | crc | crc |
105 	 * | addr | code | bytes  |       |     |       | lsb | msb |
106 	 * +------+------+--------+-------+-----+-------+-----+-----+
107 	 */
108 	char txbuf[SCD30_SERDEV_MAX_BUF_SIZE] = { SCD30_SERDEV_ADDR },
109 	     rxbuf[SCD30_SERDEV_MAX_BUF_SIZE];
110 	int ret, rxsize, txsize = 2;
111 	char *rsp = response;
112 	u16 crc;
113 
114 	put_unaligned_be16(scd30_serdev_cmd_lookup_tbl[cmd], txbuf + txsize);
115 	txsize += 2;
116 
117 	if (rsp) {
118 		txbuf[1] = SCD30_SERDEV_READ;
119 		if (cmd == CMD_READ_MEAS)
120 			/* number of u16 words to read */
121 			put_unaligned_be16(size / 2, txbuf + txsize);
122 		else
123 			put_unaligned_be16(0x0001, txbuf + txsize);
124 		txsize += 2;
125 		crc = scd30_serdev_calc_crc(txbuf, txsize);
126 		put_unaligned_le16(crc, txbuf + txsize);
127 		txsize += 2;
128 		rxsize = SCD30_SERDEV_RX_HEADER_SIZE + size + SCD30_SERDEV_CRC_SIZE;
129 	} else {
130 		if ((cmd == CMD_STOP_MEAS) || (cmd == CMD_RESET))
131 			arg = 0x0001;
132 
133 		txbuf[1] = SCD30_SERDEV_WRITE;
134 		put_unaligned_be16(arg, txbuf + txsize);
135 		txsize += 2;
136 		crc = scd30_serdev_calc_crc(txbuf, txsize);
137 		put_unaligned_le16(crc, txbuf + txsize);
138 		txsize += 2;
139 		rxsize = txsize;
140 	}
141 
142 	ret = scd30_serdev_xfer(state, txbuf, txsize, rxbuf, rxsize);
143 	if (ret)
144 		return ret;
145 
146 	switch (txbuf[1]) {
147 	case SCD30_SERDEV_WRITE:
148 		if (memcmp(txbuf, rxbuf, txsize)) {
149 			dev_err(state->dev, "wrong message received\n");
150 			return -EIO;
151 		}
152 		break;
153 	case SCD30_SERDEV_READ:
154 		if (rxbuf[2] != (rxsize - SCD30_SERDEV_RX_HEADER_SIZE - SCD30_SERDEV_CRC_SIZE)) {
155 			dev_err(state->dev, "received data size does not match header\n");
156 			return -EIO;
157 		}
158 
159 		rxsize -= SCD30_SERDEV_CRC_SIZE;
160 		crc = get_unaligned_le16(rxbuf + rxsize);
161 		if (crc != scd30_serdev_calc_crc(rxbuf, rxsize)) {
162 			dev_err(state->dev, "data integrity check failed\n");
163 			return -EIO;
164 		}
165 
166 		rxsize -= SCD30_SERDEV_RX_HEADER_SIZE;
167 		memcpy(rsp, rxbuf + SCD30_SERDEV_RX_HEADER_SIZE, rxsize);
168 		break;
169 	default:
170 		dev_err(state->dev, "received unknown op code\n");
171 		return -EIO;
172 	}
173 
174 	return 0;
175 }
176 
177 static int scd30_serdev_receive_buf(struct serdev_device *serdev,
178 				    const unsigned char *buf, size_t size)
179 {
180 	struct iio_dev *indio_dev = dev_get_drvdata(&serdev->dev);
181 	struct scd30_serdev_priv *priv;
182 	struct scd30_state *state;
183 	int num;
184 
185 	if (!indio_dev)
186 		return 0;
187 
188 	state = iio_priv(indio_dev);
189 	priv = state->priv;
190 
191 	/* just in case sensor puts some unexpected bytes on the bus */
192 	if (!priv->buf)
193 		return 0;
194 
195 	if (priv->num + size >= priv->num_expected)
196 		num = priv->num_expected - priv->num;
197 	else
198 		num = size;
199 
200 	memcpy(priv->buf + priv->num, buf, num);
201 	priv->num += num;
202 
203 	if (priv->num == priv->num_expected) {
204 		priv->buf = NULL;
205 		complete(&priv->meas_ready);
206 	}
207 
208 	return num;
209 }
210 
211 static const struct serdev_device_ops scd30_serdev_ops = {
212 	.receive_buf = scd30_serdev_receive_buf,
213 	.write_wakeup = serdev_device_write_wakeup,
214 };
215 
216 static int scd30_serdev_probe(struct serdev_device *serdev)
217 {
218 	struct device *dev = &serdev->dev;
219 	struct scd30_serdev_priv *priv;
220 	int irq, ret;
221 
222 	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
223 	if (!priv)
224 		return -ENOMEM;
225 
226 	init_completion(&priv->meas_ready);
227 	serdev_device_set_client_ops(serdev, &scd30_serdev_ops);
228 
229 	ret = devm_serdev_device_open(dev, serdev);
230 	if (ret)
231 		return ret;
232 
233 	serdev_device_set_baudrate(serdev, 19200);
234 	serdev_device_set_flow_control(serdev, false);
235 
236 	ret = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
237 	if (ret)
238 		return ret;
239 
240 	irq = fwnode_irq_get(dev_fwnode(dev), 0);
241 
242 	return scd30_probe(dev, irq, KBUILD_MODNAME, priv, scd30_serdev_command);
243 }
244 
245 static const struct of_device_id scd30_serdev_of_match[] = {
246 	{ .compatible = "sensirion,scd30" },
247 	{ }
248 };
249 MODULE_DEVICE_TABLE(of, scd30_serdev_of_match);
250 
251 static struct serdev_device_driver scd30_serdev_driver = {
252 	.driver = {
253 		.name = KBUILD_MODNAME,
254 		.of_match_table = scd30_serdev_of_match,
255 		.pm = &scd30_pm_ops,
256 	},
257 	.probe = scd30_serdev_probe,
258 };
259 module_serdev_device_driver(scd30_serdev_driver);
260 
261 MODULE_AUTHOR("Tomasz Duszynski <tomasz.duszynski@octakon.com>");
262 MODULE_DESCRIPTION("Sensirion SCD30 carbon dioxide sensor serial driver");
263 MODULE_LICENSE("GPL v2");
264