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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: Peter A. Bigot <pab@pabigot.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Peter A. Bigot 2016-12-24 07:22:44 -06:00 committed by Guenter Roeck
parent 5343aed12f
commit 53e678d75e
2 changed files with 93 additions and 4 deletions
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5
Documentation/hwmon/sht21
View File

@ -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.

92
drivers/hwmon/sht21.c
View File

@ -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
};