[PATCH] hwmon: (sht3x) Return the consumed count for heater writes

[Baek Kyu, Kim]

heater_enable_store() returns the result of i2c_master_send(), which is
the two-byte command length on success rather than the sysfs input
count. This can report more bytes than were supplied, or a partial write
for a fully processed input. For example, writing "on\n" returns two
instead of three, so a caller retrying the remaining newline gets
-EINVAL even though the heater command succeeded. Retrying the remainder
of "off\n" can also send the heater-off command twice.

Return count after a complete command transfer. Preserve negative I2C
errors and return -EIO for nonnegative incomplete transfers, so a
zero-message transfer is not reported as a successful zero-byte write.
Keep the existing boolean parsing, command selection and locking.

Fixes: 50c22cd154e5 ("hwmon: (sht3x) add humidity heater element control")
Signed-off-by: Baek Kyu, Kim <pocj8ur4in@xxxxxxxxx>
---
Tested under ARM64 QEMU with an emulated I2C adapter through hwmon
sysfs. Successful writes return the input count, and zero-message
transfers return -EIO. Retry behavior and negative I2C errors were also
checked. No physical sensor was tested.

 drivers/hwmon/sht3x.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/sht3x.c b/drivers/hwmon/sht3x.c
index b46de050e20a..a0f5ba5c888d 100644
--- a/drivers/hwmon/sht3x.c
+++ b/drivers/hwmon/sht3x.c
@@ -543,7 +543,10 @@ static ssize_t heater_enable_store(struct device *dev,
 
 	mutex_unlock(&data->i2c_lock);
 
-	return ret;
+	if (ret != SHT3X_CMD_LENGTH)
+		return ret < 0 ? ret : -EIO;
+
+	return count;
 }
 
 static int update_interval_read(struct device *dev)

base-commit: 58161ead29e50d70a317ea26b472e0c7508e69da
-- 
2.55.0