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

[PATCH] 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.

Fixes: df041e737a38 ("iio: temperature: add driver support for ti tmp117")
Signed-off-by: Salah Triki <salah.triki@gmail.com>
---
 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..7d74f401bb80 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

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

[Joshua Crofts]

On Sat, 22 Aug 2026 01:49:28 +0100
Salah Triki <salah.triki@gmail.com> wrote:

> 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.
> 
> Fixes: df041e737a38 ("iio: temperature: add driver support for ti tmp117")
> Signed-off-by: Salah Triki <salah.triki@gmail.com>
> ---
>  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..7d74f401bb80 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;

Add a blank line here.

> +		ret = i2c_smbus_write_word_swapped(data->client, TMP117_REG_TEMP_OFFSET, off);
> +

And remove the blank line here - return value checks should be grouped
with the function we're checking.

> +		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;



-- 
Kind regards,
Joshua Crofts

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

[David Lechner]

On 8/21/26 7:49 PM, Salah Triki wrote:
> 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.
> 

For fixes, it is always useful to know how you found the problem. I'm
guessing code inspection here.

> Fixes: df041e737a38 ("iio: temperature: add driver support for ti tmp117")
> Signed-off-by: Salah Triki <salah.triki@gmail.com>
> ---