--- /dev/null
+// 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");
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