// SPDX-License-Identifier: GPL-2.0
/*
* mh-z19b CO₂ sensor driver
*
* Copyright (c) 2025 Gyeyoung Baek <gye976@gmail.com>
*
* Datasheet:
* https://www.winsen-sensor.com/d/files/infrared-gas-sensor/mh-z19b-co2-ver1_0.pdf
*/
#include <linux/array_size.h>
#include <linux/completion.h>
#include <linux/device.h>
#include <linux/errno.h>
#include <linux/iio/iio.h>
#include <linux/iio/sysfs.h>
#include <linux/jiffies.h>
#include <linux/kstrtox.h>
#include <linux/minmax.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/regulator/consumer.h>
#include <linux/serdev.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/unaligned.h>
/*
* Commands have following format:
*
* +------+------+-----+------+------+------+------+------+-------+
* | 0xFF | 0x01 | cmd | arg0 | arg1 | 0x00 | 0x00 | 0x00 | cksum |
* +------+------+-----+------+------+------+------+------+-------+
*/
#define MHZ19B_CMD_SIZE 9
/* ABC logic in MHZ19B means auto calibration. */
#define MHZ19B_ABC_LOGIC_CMD 0x79
#define MHZ19B_READ_CO2_CMD 0x86
#define MHZ19B_SPAN_POINT_CMD 0x88
#define MHZ19B_ZERO_POINT_CMD 0x87
#define MHZ19B_SPAN_POINT_PPM_MIN 1000
#define MHZ19B_SPAN_POINT_PPM_MAX 5000
#define MHZ19B_SERDEV_TIMEOUT msecs_to_jiffies(100)
struct mhz19b_state {
struct serdev_device *serdev;
/* Must wait until the 'buf' is filled with 9 bytes.*/
struct completion buf_ready;
u8 buf_idx;
/*
* Serdev receive buffer.
* When data is received from the MH-Z19B,
* the 'mhz19b_receive_buf' callback function is called and fills this buffer.
*/
u8 buf[MHZ19B_CMD_SIZE] __aligned(IIO_DMA_MINALIGN);
};
static u8 mhz19b_get_checksum(u8 *cmd_buf)
{
u8 i, checksum = 0;
/*
* +------+------+-----+------+------+------+------+------+-------+
* | 0xFF | 0x01 | cmd | arg0 | arg1 | 0x00 | 0x00 | 0x00 | cksum |
* +------+------+-----+------+------+------+------+------+-------+
* i:1 2 3 4 5 6 7
*
* Sum all cmd_buf elements from index 1 to 7.
*/
for (i = 1; i < 8; i++)
checksum += cmd_buf[i];
return -checksum;
}
static int mhz19b_serdev_cmd(
struct iio_dev *indio_dev,
int cmd, u16 arg)
{
struct mhz19b_state *st = iio_priv(indio_dev);
struct serdev_device *serdev = st->serdev;
struct device *dev = &indio_dev->dev;
int ret;
/*
* cmd_buf[3,4] : arg0,1
* cmd_buf[8] : checksum
*/
u8 cmd_buf[MHZ19B_CMD_SIZE] = {
0xFF, 0x01, cmd,
};
switch (cmd) {
case MHZ19B_ABC_LOGIC_CMD:
cmd_buf[3] = arg ? 0xA0 : 0;
break;
case MHZ19B_SPAN_POINT_CMD:
put_unaligned_be16(arg, &cmd_buf[3]);
break;
default:
break;
}
cmd_buf[8] = mhz19b_get_checksum(cmd_buf);
/* Write buf to uart ctrl synchronously */
ret = serdev_device_write(serdev, cmd_buf, MHZ19B_CMD_SIZE, 0);
if (ret < 0)
return ret;
if (ret != MHZ19B_CMD_SIZE)
return -EIO;
switch (cmd) {
case MHZ19B_READ_CO2_CMD:
ret = wait_for_completion_interruptible_timeout(&st->buf_ready,
MHZ19B_SERDEV_TIMEOUT);
if (ret < 0)
return ret;
if (!ret)
return -ETIMEDOUT;
if (st->buf[8] != mhz19b_get_checksum(st->buf)) {
dev_err(dev,
"checksum err");
return -EINVAL;
}
return get_unaligned_be16(&st->buf[2]);
default:
/* No response commands. */
return 0;
}
}
static int mhz19b_read_raw(
struct iio_dev *indio_dev,
struct iio_chan_spec
const *chan,
int *val,
int *val2,
long mask)
{
int ret;
ret = mhz19b_serdev_cmd(indio_dev, MHZ19B_READ_CO2_CMD, 0);
if (ret < 0)
return ret;
*val = ret;
return IIO_VAL_INT;
}
/*
* echo 0 > calibration_auto_enable : ABC logic off
* echo 1 > calibration_auto_enable : ABC logic on
*/
static ssize_t calibration_auto_enable_store(
struct device *dev,
struct device_attribute *attr,
const char *buf, size_t len)
{
struct iio_dev *indio_dev = dev_to_iio_dev(dev);
bool enable;
int ret;
ret = kstrtobool(buf, &enable);
if (ret)
return ret;
ret = mhz19b_serdev_cmd(indio_dev, MHZ19B_ABC_LOGIC_CMD, enable);
if (ret < 0)
return ret;
return len;
}
static IIO_DEVICE_ATTR_WO(calibration_auto_enable, 0);
/*
* echo 0 > calibration_forced_value : zero point calibration
* (make sure the sensor has been working under 400ppm for over 20 minutes.)
* echo [1000 1 5000] > calibration_forced_value : span point calibration
* (make sure the sensor has been working under a certain level CO₂ for over 20 minutes.)
*/
static ssize_t calibration_forced_value_store(
struct device *dev,
struct device_attribute *attr,
const char *buf, size_t len)
{
struct iio_dev *indio_dev = dev_to_iio_dev(dev);
u16 ppm;
int cmd, ret;
ret = kstrtou16(buf, 0, &ppm);
if (ret)
return ret;
if (ppm) {
if (!in_range(ppm, MHZ19B_SPAN_POINT_PPM_MIN,
MHZ19B_SPAN_POINT_PPM_MAX - MHZ19B_SPAN_POINT_PPM_MIN + 1)) {
dev_dbg(&indio_dev->dev,
"span point ppm should be in a range [%d-%d]\n",
MHZ19B_SPAN_POINT_PPM_MIN, MHZ19B_SPAN_POINT_PPM_MAX);
return -EINVAL;
}
cmd = MHZ19B_SPAN_POINT_CMD;
}
else {
cmd = MHZ19B_ZERO_POINT_CMD;
}
ret = mhz19b_serdev_cmd(indio_dev, cmd, ppm);
if (ret < 0)
return ret;
return len;
}
static IIO_DEVICE_ATTR_WO(calibration_forced_value, 0);
static struct attribute *mhz19b_attrs[] = {
&iio_dev_attr_calibration_auto_enable.dev_attr.attr,
&iio_dev_attr_calibration_forced_value.dev_attr.attr,
NULL
};
static const struct attribute_group mhz19b_attr_group = {
.attrs = mhz19b_attrs,
};
static const struct iio_info mhz19b_info = {
.attrs = &mhz19b_attr_group,
.read_raw = mhz19b_read_raw,
};
static const struct iio_chan_spec mhz19b_channels[] = {
{
.type = IIO_CONCENTRATION,
.channel2 = IIO_MOD_CO2,
.modified = 1,
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
},
};
static size_t mhz19b_receive_buf(
struct serdev_device *serdev,
const u8 *data, size_t len)
{
struct iio_dev *indio_dev = dev_get_drvdata(&serdev->dev);
struct mhz19b_state *st = iio_priv(indio_dev);
memcpy(st->buf + st->buf_idx, data, len);
st->buf_idx += len;
if (st->buf_idx == MHZ19B_CMD_SIZE) {
st->buf_idx = 0;
complete(&st->buf_ready);
}
return len;
}
static const struct serdev_device_ops mhz19b_ops = {
.receive_buf = mhz19b_receive_buf,
.write_wakeup = serdev_device_write_wakeup,
};
static int mhz19b_probe(
struct serdev_device *serdev)
{
int ret;
struct device *dev = &serdev->dev;
struct iio_dev *indio_dev;
struct mhz19b_state *st;
serdev_device_set_client_ops(serdev, &mhz19b_ops);
ret = devm_serdev_device_open(dev, serdev);
if (ret)
return ret;
serdev_device_set_baudrate(serdev, 9600);
serdev_device_set_flow_control(serdev,
false);
ret = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
if (ret)
return ret;
indio_dev = devm_iio_device_alloc(dev,
sizeof(*st));
if (!indio_dev)
return -ENOMEM;
serdev_device_set_drvdata(serdev, indio_dev);
st = iio_priv(indio_dev);
st->serdev = serdev;
init_completion(&st->buf_ready);
ret = devm_regulator_get_enable(dev,
"vin");
if (ret)
return ret;
indio_dev->name =
"mh-z19b";
indio_dev->channels = mhz19b_channels;
indio_dev->num_channels = ARRAY_SIZE(mhz19b_channels);
indio_dev->info = &mhz19b_info;
return devm_iio_device_register(dev, indio_dev);
}
static const struct of_device_id mhz19b_of_match[] = {
{ .compatible =
"winsen,mhz19b", },
{ }
};
MODULE_DEVICE_TABLE(of, mhz19b_of_match);
static struct serdev_device_driver mhz19b_driver = {
.driver = {
.name =
"mhz19b",
.of_match_table = mhz19b_of_match,
},
.probe = mhz19b_probe,
};
module_serdev_device_driver(mhz19b_driver);
MODULE_AUTHOR(
"Gyeyoung Baek");
MODULE_DESCRIPTION(
"MH-Z19B CO2 sensor driver using serdev interface");
MODULE_LICENSE(
"GPL");
