hwmon: Add AHT10 Temperature and Humidity Sensor Driver

This patch adds a hwmon driver for the AHT10 Temperature and
Humidity sensor. It has a maximum sample rate, as the datasheet
states that the chip may heat up if it is sampled more than once
every two seconds.

Has been tested a to work on a raspberrypi0w

Signed-off-by: Johannes Cornelis Draaijer (datdenkikniet) <jcdra1@gmail.com>
Link: https://lore.kernel.org/r/20210107194014.GA88780@desktop
[groeck: dropped AHT10_ADDR (unused) and use AHT10_MEAS_SIZE where
 appropriate; dropped change log]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/aht10.rst

@@ -0,0 +1,46 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Kernel driver aht10
+=====================
+
+Supported chips:
+
+  * Aosong AHT10
+
+    Prefix: 'aht10'
+
+    Addresses scanned: None
+
+    Datasheet:
+
+      Chinese: http://www.aosong.com/userfiles/files/media/AHT10%E4%BA%A7%E5%93%81%E6%89%8B%E5%86%8C%20A3%2020201210.pdf
+      English: https://server4.eca.ir/eshop/AHT10/Aosong_AHT10_en_draft_0c.pdf
+
+Author: Johannes Cornelis Draaijer <jcdra1@gmail.com>
+
+
+Description
+-----------
+
+The AHT10 is a Temperature and Humidity sensor
+
+The address of this i2c device may only be 0x38
+
+Usage Notes
+-----------
+
+This driver does not probe for AHT10 devices, as there is no reliable
+way to determine if an i2c chip is or isn't an AHT10. The device has
+to be instantiated explicitly with the address 0x38. See
+Documentation/i2c/instantiating-devices.rst for details.
+
+Sysfs entries
+-------------
+
+=============== ============================================
+temp1_input     Measured temperature in millidegrees Celcius
+humidity1_input Measured humidity in %H
+update_interval The minimum interval for polling the sensor,
+                in milliseconds. Writable. Must be at
+                least 2000.
+=============== ============================================

Documentation/hwmon/index.rst

@@ -37,6 +37,7 @@ Hardware Monitoring Kernel Drivers
    adt7462
    adt7470
    adt7475
+   aht10
    amc6821
    amd_energy
    asb100

drivers/hwmon/Kconfig

@@ -244,6 +244,16 @@ config SENSORS_ADT7475
 	  This driver can also be built as a module. If so, the module
 	  will be called adt7475.
 
+config SENSORS_AHT10
+	tristate "Aosong AHT10"
+	depends on I2C
+	help
+	  If you say yes here, you get support for the Aosong AHT10
+	  temperature and humidity sensors
+
+	  This driver can also be built as a module. If so, the module
+	  will be called aht10.
+
 config SENSORS_AS370
 	tristate "Synaptics AS370 SoC hardware monitoring driver"
 	help

drivers/hwmon/Makefile

@@ -44,6 +44,7 @@ obj-$(CONFIG_SENSORS_ADT7411)	+= adt7411.o
 obj-$(CONFIG_SENSORS_ADT7462)	+= adt7462.o
 obj-$(CONFIG_SENSORS_ADT7470)	+= adt7470.o
 obj-$(CONFIG_SENSORS_ADT7475)	+= adt7475.o
+obj-$(CONFIG_SENSORS_AHT10)	+= aht10.o
 obj-$(CONFIG_SENSORS_AMD_ENERGY) += amd_energy.o
 obj-$(CONFIG_SENSORS_APPLESMC)	+= applesmc.o
 obj-$(CONFIG_SENSORS_ARM_SCMI)	+= scmi-hwmon.o

drivers/hwmon/aht10.c

@@ -0,0 +1,346 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * aht10.c - Linux hwmon driver for AHT10 Temperature and Humidity sensor
+ * Copyright (C) 2020 Johannes Cornelis Draaijer
+ */
+
+#include <linux/delay.h>
+#include <linux/hwmon.h>
+#include <linux/i2c.h>
+#include <linux/ktime.h>
+#include <linux/module.h>
+
+#define AHT10_MEAS_SIZE		6
+
+/*
+ * Poll intervals (in milliseconds)
+ */
+#define AHT10_DEFAULT_MIN_POLL_INTERVAL	2000
+#define AHT10_MIN_POLL_INTERVAL		2000
+
+/*
+ * I2C command delays (in microseconds)
+ */
+#define AHT10_MEAS_DELAY	80000
+#define AHT10_CMD_DELAY		350000
+#define AHT10_DELAY_EXTRA	100000
+
+/*
+ * Command bytes
+ */
+#define AHT10_CMD_INIT	0b11100001
+#define AHT10_CMD_MEAS	0b10101100
+#define AHT10_CMD_RST	0b10111010
+
+/*
+ * Flags in the answer byte/command
+ */
+#define AHT10_CAL_ENABLED	BIT(3)
+#define AHT10_BUSY		BIT(7)
+#define AHT10_MODE_NOR		(BIT(5) | BIT(6))
+#define AHT10_MODE_CYC		BIT(5)
+#define AHT10_MODE_CMD		BIT(6)
+
+#define AHT10_MAX_POLL_INTERVAL_LEN	30
+
+/**
+ *   struct aht10_data - All the data required to operate an AHT10 chip
+ *   @client: the i2c client associated with the AHT10
+ *   @lock: a mutex that is used to prevent parallel access to the
+ *          i2c client
+ *   @min_poll_interval: the minimum poll interval
+ *                   While the poll rate limit is not 100% necessary,
+ *                   the datasheet recommends that a measurement
+ *                   is not performed too often to prevent
+ *                   the chip from warming up due to the heat it generates.
+ *                   If it's unwanted, it can be ignored setting it to
+ *                   it to 0. Default value is 2000 ms
+ *   @previous_poll_time: the previous time that the AHT10
+ *                        was polled
+ *   @temperature: the latest temperature value received from
+ *                 the AHT10
+ *   @humidity: the latest humidity value received from the
+ *              AHT10
+ */
+
+struct aht10_data {
+	struct i2c_client *client;
+	/*
+	 * Prevent simultaneous access to the i2c
+	 * client and previous_poll_time
+	 */
+	struct mutex lock;
+	ktime_t min_poll_interval;
+	ktime_t previous_poll_time;
+	int temperature;
+	int humidity;
+};
+
+/**
+ * aht10_init() - Initialize an AHT10 chip
+ * @client: the i2c client associated with the AHT10
+ * @data: the data associated with this AHT10 chip
+ * Return: 0 if succesfull, 1 if not
+ */
+static int aht10_init(struct aht10_data *data)
+{
+	const u8 cmd_init[] = {AHT10_CMD_INIT, AHT10_CAL_ENABLED | AHT10_MODE_CYC,
+			       0x00};
+	int res;
+	u8 status;
+	struct i2c_client *client = data->client;
+
+	res = i2c_master_send(client, cmd_init, 3);
+	if (res < 0)
+		return res;
+
+	usleep_range(AHT10_CMD_DELAY, AHT10_CMD_DELAY +
+		     AHT10_DELAY_EXTRA);
+
+	res = i2c_master_recv(client, &status, 1);
+	if (res != 1)
+		return -ENODATA;
+
+	if (status & AHT10_BUSY)
+		return -EBUSY;
+
+	return 0;
+}
+
+/**
+ * aht10_polltime_expired() - check if the minimum poll interval has
+ *                                  expired
+ * @data: the data containing the time to compare
+ * Return: 1 if the minimum poll interval has expired, 0 if not
+ */
+static int aht10_polltime_expired(struct aht10_data *data)
+{
+	ktime_t current_time = ktime_get_boottime();
+	ktime_t difference = ktime_sub(current_time, data->previous_poll_time);
+
+	return ktime_after(difference, data->min_poll_interval);
+}
+
+/**
+ * aht10_read_values() - read and parse the raw data from the AHT10
+ * @aht10_data: the struct aht10_data to use for the lock
+ * Return: 0 if succesfull, 1 if not
+ */
+static int aht10_read_values(struct aht10_data *data)
+{
+	const u8 cmd_meas[] = {AHT10_CMD_MEAS, 0x33, 0x00};
+	u32 temp, hum;
+	int res;
+	u8 raw_data[AHT10_MEAS_SIZE];
+	struct i2c_client *client = data->client;
+
+	mutex_lock(&data->lock);
+	if (aht10_polltime_expired(data)) {
+		res = i2c_master_send(client, cmd_meas, sizeof(cmd_meas));
+		if (res < 0)
+			return res;
+
+		usleep_range(AHT10_MEAS_DELAY,
+			     AHT10_MEAS_DELAY + AHT10_DELAY_EXTRA);
+
+		res = i2c_master_recv(client, raw_data, AHT10_MEAS_SIZE);
+		if (res != AHT10_MEAS_SIZE) {
+			mutex_unlock(&data->lock);
+			if (res >= 0)
+				return -ENODATA;
+			else
+				return res;
+		}
+
+		hum =   ((u32)raw_data[1] << 12u) |
+			((u32)raw_data[2] << 4u) |
+			((raw_data[3] & 0xF0u) >> 4u);
+
+		temp =  ((u32)(raw_data[3] & 0x0Fu) << 16u) |
+			((u32)raw_data[4] << 8u) |
+			raw_data[5];
+
+		temp = ((temp * 625) >> 15u) * 10;
+		hum = ((hum * 625) >> 16u) * 10;
+
+		data->temperature = (int)temp - 50000;
+		data->humidity = hum;
+		data->previous_poll_time = ktime_get_boottime();
+	}
+	mutex_unlock(&data->lock);
+	return 0;
+}
+
+/**
+ * aht10_interval_write() - store the given minimum poll interval.
+ * Return: 0 on success, -EINVAL if a value lower than the
+ *         AHT10_MIN_POLL_INTERVAL is given
+ */
+static ssize_t aht10_interval_write(struct aht10_data *data,
+				    long val)
+{
+	data->min_poll_interval = ms_to_ktime(clamp_val(val, 2000, LONG_MAX));
+	return 0;
+}
+
+/**
+ * aht10_interval_read() - read the minimum poll interval
+ *                            in milliseconds
+ */
+static ssize_t aht10_interval_read(struct aht10_data *data,
+				   long *val)
+{
+	*val = ktime_to_ms(data->min_poll_interval);
+	return 0;
+}
+
+/**
+ * aht10_temperature1_read() - read the temperature in millidegrees
+ */
+static int aht10_temperature1_read(struct aht10_data *data, long *val)
+{
+	int res;
+
+	res = aht10_read_values(data);
+	if (res < 0)
+		return res;
+
+	*val = data->temperature;
+	return 0;
+}
+
+/**
+ * aht10_humidity1_read() - read the relative humidity in millipercent
+ */
+static int aht10_humidity1_read(struct aht10_data *data, long *val)
+{
+	int res;
+
+	res = aht10_read_values(data);
+	if (res < 0)
+		return res;
+
+	*val = data->humidity;
+	return 0;
+}
+
+static umode_t aht10_hwmon_visible(const void *data, enum hwmon_sensor_types type,
+				   u32 attr, int channel)
+{
+	switch (type) {
+	case hwmon_temp:
+	case hwmon_humidity:
+		return 0444;
+	case hwmon_chip:
+		return 0644;
+	default:
+		return 0;
+	}
+}
+
+static int aht10_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
+			    u32 attr, int channel, long *val)
+{
+	struct aht10_data *data = dev_get_drvdata(dev);
+
+	switch (type) {
+	case hwmon_temp:
+		return aht10_temperature1_read(data, val);
+	case hwmon_humidity:
+		return aht10_humidity1_read(data, val);
+	case hwmon_chip:
+		return aht10_interval_read(data, val);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static int aht10_hwmon_write(struct device *dev, enum hwmon_sensor_types type,
+			     u32 attr, int channel, long val)
+{
+	struct aht10_data *data = dev_get_drvdata(dev);
+
+	switch (type) {
+	case hwmon_chip:
+		return aht10_interval_write(data, val);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static const struct hwmon_channel_info *aht10_info[] = {
+	HWMON_CHANNEL_INFO(chip, HWMON_C_UPDATE_INTERVAL),
+	HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT),
+	HWMON_CHANNEL_INFO(humidity, HWMON_H_INPUT),
+	NULL,
+};
+
+static const struct hwmon_ops aht10_hwmon_ops = {
+	.is_visible = aht10_hwmon_visible,
+	.read = aht10_hwmon_read,
+	.write = aht10_hwmon_write,
+};
+
+static const struct hwmon_chip_info aht10_chip_info = {
+	.ops = &aht10_hwmon_ops,
+	.info = aht10_info,
+};
+
+static int aht10_probe(struct i2c_client *client,
+		       const struct i2c_device_id *aht10_id)
+{
+	struct device *device = &client->dev;
+	struct device *hwmon_dev;
+	struct aht10_data *data;
+	int res;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
+		return -ENOENT;
+
+	data = devm_kzalloc(device, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->min_poll_interval = ms_to_ktime(AHT10_DEFAULT_MIN_POLL_INTERVAL);
+	data->client = client;
+
+	mutex_init(&data->lock);
+
+	res = aht10_init(data);
+	if (res < 0)
+		return res;
+
+	res = aht10_read_values(data);
+	if (res < 0)
+		return res;
+
+	hwmon_dev = devm_hwmon_device_register_with_info(device,
+							 client->name,
+							 data,
+							 &aht10_chip_info,
+							 NULL);
+
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct i2c_device_id aht10_id[] = {
+	{ "aht10", 0 },
+	{ },
+};
+MODULE_DEVICE_TABLE(i2c, aht10_id);
+
+static struct i2c_driver aht10_driver = {
+	.driver = {
+		.name = "aht10",
+	},
+	.probe      = aht10_probe,
+	.id_table   = aht10_id,
+};
+
+module_i2c_driver(aht10_driver);
+
+MODULE_AUTHOR("Johannes Cornelis Draaijer <jcdra1@gmail.com>");
+MODULE_DESCRIPTION("AHT10 Temperature and Humidity sensor driver");
+MODULE_VERSION("1.0");
+MODULE_LICENSE("GPL v2");