[PATCH v2] iio: temperature: tmp117: fix calibbias cache update on I2C write failure

[Salah Triki]

The calibbias cache (data->calibbias) was updated before the I2C
write to TMP117_REG_TEMP_OFFSET was known to succeed. If the write
failed, the function correctly returned an error, but the driver's
internal cache had already been updated to the new value.

This causes the cache and the actual hardware register to go out of
sync: a subsequent write of the same value would be silently
skipped by the early "if (off == data->calibbias) return 0;" check,
since the cache matches even though the register was never
successfully updated.

Update data->calibbias only after confirming the I2C write
succeeded, so the cache always reflects the actual state of the
device.

Found by code inspection.

Fixes: df041e737a38 ("iio: temperature: add driver support for ti tmp117")
Signed-off-by: Salah Triki <salah.triki@xxxxxxxxx>
---
Changes since v2:
- Fixed formatting around ret assignment and check (Joshua Crofts).
- Mentioned in commit description that the issue was found by code inspection (David Lechner).

 drivers/iio/temperature/tmp117.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/temperature/tmp117.c b/drivers/iio/temperature/tmp117.c
index 6bc18616ad15..a07028d560ba 100644
--- a/drivers/iio/temperature/tmp117.c
+++ b/drivers/iio/temperature/tmp117.c
@@ -95,15 +95,20 @@ static int tmp117_write_raw(struct iio_dev *indio_dev, struct iio_chan_spec
 {
 	struct tmp117_data *data = iio_priv(indio_dev);
 	s16 off;
+	int ret;
 
 	switch (mask) {
 	case IIO_CHAN_INFO_CALIBBIAS:
 		off = clamp_t(int, val, S16_MIN, S16_MAX);
 		if (off == data->calibbias)
 			return 0;
+
+		ret = i2c_smbus_write_word_swapped(data->client, TMP117_REG_TEMP_OFFSET, off);
+		if (ret)
+			return ret;
+
 		data->calibbias = off;
-		return i2c_smbus_write_word_swapped(data->client,
-						TMP117_REG_TEMP_OFFSET, off);
+		return 0;
 
 	default:
 		return -EINVAL;
-- 
2.43.0