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
30struct scd30_serdev_priv {
31	struct completion meas_ready;
32	char *buf;
33	int num_expected;
34	int num;
35};
36
37static 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
50static u16 scd30_serdev_calc_crc(const char *buf, int size)
51{
52	return crc16(0xffff, buf, size);
53}
54
55static 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
81static 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
177static 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
211static const struct serdev_device_ops scd30_serdev_ops = {
212	.receive_buf = scd30_serdev_receive_buf,
213	.write_wakeup = serdev_device_write_wakeup,
214};
215
216static 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
245static const struct of_device_id scd30_serdev_of_match[] = {
246	{ .compatible = "sensirion,scd30" },
247	{ }
248};
249MODULE_DEVICE_TABLE(of, scd30_serdev_of_match);
250
251static 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};
259module_serdev_device_driver(scd30_serdev_driver);
260
261MODULE_AUTHOR("Tomasz Duszynski <tomasz.duszynski@octakon.com>");
262MODULE_DESCRIPTION("Sensirion SCD30 carbon dioxide sensor serial driver");
263MODULE_LICENSE("GPL v2");
264