iio: chemical: add support for Aosong AGS02MA

A simple driver for the TVOC (Total Volatile Organic Compounds)
sensor from Aosong: AGS02MA

Steps in reading the VOC sensor value over i2c:
1. Read 5 bytes from the register `AGS02MA_TVOC_READ_REG` [0x00]
2. The first 4 bytes are taken as the big endian sensor data with final
byte being the CRC
3. The CRC is verified and the value is returned over an
`IIO_CHAN_INFO_RAW` channel as percents

Tested on Raspberry Pi Zero 2W

Datasheet: https://asairsensors.com/wp-content/uploads/2021/09/AGS02MA.pdf
Signed-off-by: Anshul Dalal <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

MAINTAINERS

···
 W:	http://www.akm.com/
 F:	drivers/iio/magnetometer/ak8974.c
 
+AOSONG AGS02MA TVOC SENSOR DRIVER
+M:	Anshul Dalal <[e-mail]>
+L:	[e-mail]
+S:	Maintained
+F:	Documentation/devicetree/bindings/iio/chemical/aosong,ags02ma.yaml
+F:	drivers/iio/chemical/ags02ma.c
+
 ASC7621 HARDWARE MONITOR DRIVER
 M:	George Joseph <[e-mail]>
 L:	[e-mail]

drivers/iio/chemical/Kconfig

···
 
 menu "Chemical Sensors"
 
+config AOSONG_AGS02MA
+	tristate "Aosong AGS02MA TVOC sensor driver"
+	depends on I2C
+	select CRC8
+	help
+	  Say Y here to build support for Aosong AGS02MA TVOC (Total Volatile
+	  Organic Compounds) sensor.
+
+	  To compile this driver as module, choose M here: the module will be
+	  called ags02ma.
+
 config ATLAS_PH_SENSOR
 	tristate "Atlas Scientific OEM SM sensors"
 	depends on I2C

drivers/iio/chemical/Makefile

···
 #
 
 # When adding new entries keep the list in alphabetical order
+obj-$(CONFIG_AOSONG_AGS02MA)	+= ags02ma.o
 obj-$(CONFIG_ATLAS_PH_SENSOR)	+= atlas-sensor.o
 obj-$(CONFIG_ATLAS_EZO_SENSOR)	+= atlas-ezo-sensor.o
 obj-$(CONFIG_BME680) += bme680_core.o

drivers/iio/chemical/ags02ma.c

···
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2023 Anshul Dalal <[e-mail]>
+ *
+ * Driver for Aosong AGS02MA
+ *
+ * Datasheet:
+ *   https://asairsensors.com/wp-content/uploads/2021/09/AGS02MA.pdf
+ * Product Page:
+ *   http://www.aosong.com/m/en/products-33.html
+ */
+
+#include <linux/crc8.h>
+#include <linux/delay.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+
+#include <linux/iio/iio.h>
+
+#define AGS02MA_TVOC_READ_REG		   0x00
+#define AGS02MA_VERSION_REG		   0x11
+
+#define AGS02MA_VERSION_PROCESSING_DELAY   30
+#define AGS02MA_TVOC_READ_PROCESSING_DELAY 1500
+
+#define AGS02MA_CRC8_INIT		   0xff
+#define AGS02MA_CRC8_POLYNOMIAL		   0x31
+
+DECLARE_CRC8_TABLE(ags02ma_crc8_table);
+
+struct ags02ma_data {
+	struct i2c_client *client;
+};
+
+struct ags02ma_reading {
+	__be32 data;
+	u8 crc;
+} __packed;
+
+static int ags02ma_register_read(struct i2c_client *client, u8 reg, u16 delay,
+				 u32 *val)
+{
+	int ret;
+	u8 crc;
+	struct ags02ma_reading read_buffer;
+
+	ret = i2c_master_send(client, &reg, sizeof(reg));
+	if (ret < 0) {
+		dev_err(&client->dev,
+			"Failed to send data to register 0x%x: %d", reg, ret);
+		return ret;
+	}
+
+	/* Processing Delay, Check Table 7.7 in the datasheet */
+	msleep_interruptible(delay);
+
+	ret = i2c_master_recv(client, (u8 *)&read_buffer, sizeof(read_buffer));
+	if (ret < 0) {
+		dev_err(&client->dev,
+			"Failed to receive from register 0x%x: %d", reg, ret);
+		return ret;
+	}
+
+	crc = crc8(ags02ma_crc8_table, (u8 *)&read_buffer.data,
+		   sizeof(read_buffer.data), AGS02MA_CRC8_INIT);
+	if (crc != read_buffer.crc) {
+		dev_err(&client->dev, "CRC error\n");
+		return -EIO;
+	}
+
+	*val = be32_to_cpu(read_buffer.data);
+	return 0;
+}
+
+static int ags02ma_read_raw(struct iio_dev *iio_device,
+			    struct iio_chan_spec const *chan, int *val,
+			    int *val2, long mask)
+{
+	int ret;
+	struct ags02ma_data *data = iio_priv(iio_device);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = ags02ma_register_read(data->client, AGS02MA_TVOC_READ_REG,
+					    AGS02MA_TVOC_READ_PROCESSING_DELAY,
+					    val);
+		if (ret < 0)
+			return ret;
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		/* The sensor reads data as ppb */
+		*val = 0;
+		*val2 = 100;
+		return IIO_VAL_INT_PLUS_NANO;
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info ags02ma_info = {
+	.read_raw = ags02ma_read_raw,
+};
+
+static const struct iio_chan_spec ags02ma_channel = {
+	.type = IIO_CONCENTRATION,
+	.channel2 = IIO_MOD_VOC,
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+		BIT(IIO_CHAN_INFO_SCALE),
+};
+
+static int ags02ma_probe(struct i2c_client *client)
+{
+	int ret;
+	struct ags02ma_data *data;
+	struct iio_dev *indio_dev;
+	u32 version;
+
+	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	crc8_populate_msb(ags02ma_crc8_table, AGS02MA_CRC8_POLYNOMIAL);
+
+	ret = ags02ma_register_read(client, AGS02MA_VERSION_REG,
+				    AGS02MA_VERSION_PROCESSING_DELAY, &version);
+	if (ret < 0)
+		return dev_err_probe(&client->dev, ret,
+			      "Failed to read device version\n");
+	dev_dbg(&client->dev, "Aosong AGS02MA, Version: 0x%x", version);
+
+	data = iio_priv(indio_dev);
+	data->client = client;
+	indio_dev->info = &ags02ma_info;
+	indio_dev->channels = &ags02ma_channel;
+	indio_dev->num_channels = 1;
+	indio_dev->name = "ags02ma";
+
+	return devm_iio_device_register(&client->dev, indio_dev);
+}
+
+static const struct i2c_device_id ags02ma_id_table[] = {
+	{ "ags02ma" },
+	{ /* Sentinel */ }
+};
+MODULE_DEVICE_TABLE(i2c, ags02ma_id_table);
+
+static const struct of_device_id ags02ma_of_table[] = {
+	{ .compatible = "aosong,ags02ma" },
+	{ /* Sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, ags02ma_of_table);
+
+static struct i2c_driver ags02ma_driver = {
+	.driver = {
+		.name = "ags02ma",
+		.of_match_table = ags02ma_of_table,
+	},
+	.id_table = ags02ma_id_table,
+	.probe = ags02ma_probe,
+};
+module_i2c_driver(ags02ma_driver);
+
+MODULE_AUTHOR("Anshul Dalal <[e-mail]>");
+MODULE_DESCRIPTION("Aosong AGS02MA TVOC Driver");
+MODULE_LICENSE("GPL");