Commit 53e678d7 authored by Peter A. Bigot's avatar Peter A. Bigot Committed by Guenter Roeck
Browse files

hwmon: (sht21) Add Electronic Identification Code retrieval 



Expose the per-chip unique identifier so it can be used to identify the
sensor producing the measurements.

Signed-off-by: default avatarPeter A. Bigot <pab@pabigot.com>
Signed-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
parent 5343aed1

Documentation/hwmon/sht21

+3 −2
Original line number Diff line number Diff line
@@ -35,6 +35,7 @@ sysfs-Interface 


temp1_input - temperature input

humidity1_input - humidity input

eic - Electronic Identification Code



Notes

-----
@@ -45,5 +46,5 @@ humidity and 66 ms for temperature. To keep self heating below 0.1 degree 
Celsius, the device should not be active for more than 10% of the time,

e.g. maximum two measurements per second at the given resolution.



Different resolutions, the on-chip heater, using the CRC checksum and reading

the serial number are not supported yet.
 
Different resolutions, the on-chip heater, and using the CRC checksum

are not supported yet.

drivers/hwmon/sht21.c

+90 −2
Original line number Diff line number Diff line
@@ -34,23 +34,29 @@ 
/* I2C command bytes */

#define SHT21_TRIG_T_MEASUREMENT_HM  0xe3

#define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5

#define SHT21_READ_SNB_CMD1 0xFA

#define SHT21_READ_SNB_CMD2 0x0F

#define SHT21_READ_SNAC_CMD1 0xFC

#define SHT21_READ_SNAC_CMD2 0xC9



/**

 * struct sht21 - SHT21 device specific data

 * @hwmon_dev: device registered with hwmon

 * @lock: mutex to protect measurement values

 * @valid: only 0 before first measurement is taken

 * @last_update: time of last update (jiffies)

 * @temperature: cached temperature measurement value

 * @humidity: cached humidity measurement value

 * @valid: only 0 before first measurement is taken

 * @eic: cached electronic identification code text

 */

struct sht21 {

	struct i2c_client *client;

	struct mutex lock;

	char valid;

	unsigned long last_update;

	int temperature;

	int humidity;

	char valid;

	char eic[18];

};



/**
@@ -165,15 +171,97 @@ static ssize_t sht21_show_humidity(struct device *dev, 
	return sprintf(buf, "%d\n", sht21->humidity);

}



static ssize_t eic_read(struct sht21 *sht21)

{

	struct i2c_client *client = sht21->client;

	u8 tx[2];

	u8 rx[8];

	u8 eic[8];

	struct i2c_msg msgs[2] = {

		{

			.addr = client->addr,

			.flags = 0,

			.len = 2,

			.buf = tx,

		},

		{

			.addr = client->addr,

			.flags = I2C_M_RD,

			.len = 8,

			.buf = rx,

		},

	};

	int ret;



	tx[0] = SHT21_READ_SNB_CMD1;

	tx[1] = SHT21_READ_SNB_CMD2;

	ret = i2c_transfer(client->adapter, msgs, 2);

	if (ret < 0)

		goto out;

	eic[2] = rx[0];

	eic[3] = rx[2];

	eic[4] = rx[4];

	eic[5] = rx[6];



	tx[0] = SHT21_READ_SNAC_CMD1;

	tx[1] = SHT21_READ_SNAC_CMD2;

	msgs[1].len = 6;

	ret = i2c_transfer(client->adapter, msgs, 2);

	if (ret < 0)

		goto out;

	eic[0] = rx[3];

	eic[1] = rx[4];

	eic[6] = rx[0];

	eic[7] = rx[1];



	ret = snprintf(sht21->eic, sizeof(sht21->eic),

		       "%02x%02x%02x%02x%02x%02x%02x%02x\n",

		       eic[0], eic[1], eic[2], eic[3],

		       eic[4], eic[5], eic[6], eic[7]);

out:

	if (ret < 0)

		sht21->eic[0] = 0;



	return ret;

}



/**

 * eic_show() - show Electronic Identification Code in sysfs

 * @dev: device

 * @attr: device attribute

 * @buf: sysfs buffer (PAGE_SIZE) where EIC is written

 *

 * Will be called on read access to eic sysfs attribute.

 * Returns number of bytes written into buffer, negative errno on error.

 */

static ssize_t eic_show(struct device *dev,

	struct device_attribute *attr,

	char *buf)

{

	struct sht21 *sht21 = dev_get_drvdata(dev);

	int ret;



	ret = sizeof(sht21->eic) - 1;

	mutex_lock(&sht21->lock);

	if (!sht21->eic[0])

		ret = eic_read(sht21);

	if (ret > 0)

		memcpy(buf, sht21->eic, ret);

	mutex_unlock(&sht21->lock);

	return ret;

}



/* sysfs attributes */

static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,

	NULL, 0);

static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,

	NULL, 0);

static DEVICE_ATTR_RO(eic);



static struct attribute *sht21_attrs[] = {

	&sensor_dev_attr_temp1_input.dev_attr.attr,

	&sensor_dev_attr_humidity1_input.dev_attr.attr,

	&dev_attr_eic.attr,

	NULL

};