Some I2C bus drivers do not allow zero-length data transfers which are
required to start a measurement with the HIH6130/1 sensor. Nevertheless,
we can overcome this limitation by writing a zero dummy byte. This byte
is ignored by the sensor and was verified to be working with the OMAP
I2C bus driver in a BeagleBone board.
Signed-off-by: José Miguel Gonçalves <jose.goncalves@xxxxxxx>
---
v2: Use a field in struct hih6130 to store the measurement request's
write length when probing.
drivers/hwmon/hih6130.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/drivers/hwmon/hih6130.c b/drivers/hwmon/hih6130.c
index 2dc37c7..8e46265 100644
--- a/drivers/hwmon/hih6130.c
+++ b/drivers/hwmon/hih6130.c
@@ -43,6 +43,7 @@
* @last_update: time of last update (jiffies)
* @temperature: cached temperature measurement value
* @humidity: cached humidity measurement value
+ * @write_length: length for I2C measurement request
*/
struct hih6130 {
struct device *hwmon_dev;
@@ -51,6 +52,7 @@ struct hih6130 {
unsigned long last_update;
int temperature;
int humidity;
+ size_t write_length;
};
/**
@@ -121,8 +123,15 @@ static int hih6130_update_measurements(struct i2c_client *client)
*/
if (time_after(jiffies, hih6130->last_update + HZ) || !hih6130->valid) {
- /* write to slave address, no data, to request a measurement */
- ret = i2c_master_send(client, tmp, 0);
+ /*
+ * 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;
@@ -252,6 +261,9 @@ static int hih6130_probe(struct i2c_client *client,
goto fail_remove_sysfs;
}
+ hih6130->write_length = (i2c_get_functionality(client->adapter) &
+ I2C_FUNC_SMBUS_QUICK ? 0 : 1);
+
return 0;
fail_remove_sysfs:
--
1.7.10.4
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