drivers/hwmon/hih6130.c

Source file repositories/reference/linux-study-clean/drivers/hwmon/hih6130.c

File Facts

System
Linux kernel
Corpus path
drivers/hwmon/hih6130.c
Extension
.c
Size
7229 bytes
Lines
261
Domain
Driver Families
Bucket
drivers/hwmon
Inferred role
Driver Families: implementation source
Status
source implementation candidate

Why This File Exists

Repeatable hardware-adapter layer. Deep compatibility for every driver is out of scope; this atlas records patterns, probe lifecycles, bus glue, IRQ/DMA usage, and links back to core abstractions.

Dependency Surface

Detected Declarations

Annotated Snippet

struct hih6130 {
	struct i2c_client *client;
	struct mutex lock;
	bool valid;
	unsigned long last_update;
	int temperature;
	int humidity;
	size_t write_length;
};

/**
 * hih6130_temp_ticks_to_millicelsius() - convert raw temperature ticks to
 * milli celsius
 * @ticks: temperature ticks value received from sensor
 */
static inline int hih6130_temp_ticks_to_millicelsius(int ticks)
{
	ticks = ticks >> 2;
	/*
	 * from data sheet section 5.0
	 * Formula T = ( ticks / ( 2^14 - 2 ) ) * 165 -40
	 */
	return (DIV_ROUND_CLOSEST(ticks * 1650, 16382) - 400) * 100;
}

/**
 * hih6130_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
 * one-thousandths of a percent relative humidity
 * @ticks: humidity ticks value received from sensor
 */
static inline int hih6130_rh_ticks_to_per_cent_mille(int ticks)
{
	ticks &= ~0xC000; /* clear status bits */
	/*
	 * from data sheet section 4.0
	 * Formula RH = ( ticks / ( 2^14 -2 ) ) * 100
	 */
	return DIV_ROUND_CLOSEST(ticks * 1000, 16382) * 100;
}

/**
 * hih6130_update_measurements() - get updated measurements from device
 * @dev: device
 *
 * Returns 0 on success, else negative errno.
 */
static int hih6130_update_measurements(struct device *dev)
{
	struct hih6130 *hih6130 = dev_get_drvdata(dev);
	struct i2c_client *client = hih6130->client;
	int ret = 0;
	int t;
	unsigned char tmp[4];
	struct i2c_msg msgs[1] = {
		{
			.addr = client->addr,
			.flags = I2C_M_RD,
			.len = 4,
			.buf = tmp,
		}
	};

	mutex_lock(&hih6130->lock);

	/*
	 * While the measurement can be completed in ~40ms the sensor takes
	 * much longer to react to a change in external conditions. How quickly
	 * it reacts depends on airflow and other factors outwith our control.
	 * The datasheet specifies maximum 'Response time' for humidity at 8s
	 * and temperature at 30s under specified conditions.
	 * We therefore choose to only read the sensor at most once per second.
	 * This trades off pointless activity polling the sensor much faster
	 * than it can react against better response times in conditions more
	 * favourable than specified in the datasheet.
	 */
	if (time_after(jiffies, hih6130->last_update + HZ) || !hih6130->valid) {

		/*
		 * Write to slave address to request a measurement.
		 * According with the datasheet it should be with no data, but
		 * for systems with I2C bus drivers that do not allow zero
		 * length packets we write one dummy byte to allow sensor
		 * measurements on them.
		 */
		tmp[0] = 0;
		ret = i2c_master_send(client, tmp, hih6130->write_length);
		if (ret < 0)
			goto out;

		/* measurement cycle time is ~36.65msec */

Annotation

Implementation Notes