The current implementation of tsys01_crc_valid() incorrectly sums the
first word (n_prom[0]) repeatedly instead of iterating over the 8 words
retrieved from the PROM. This leads to a checksum mismatch and probe
failure on hardware.

According to the TSYS01 datasheet, the PROM consists of 8 words. A valid
check must iterate through all 8 words to verify the integrity of the
calibration data. The current driver only checks the first word 8 times.

Note: This fix was identified during a code audit and is based on
datasheet specifications. It has not been tested on real hardware.

Fixes: 43e53407f680 ("Add tsys01 meas-spec driver support")
Signed-off-by: Salah Triki <salah.triki@gmail.com>
---
Changes in v2:
   - Update commit message to clarify that the fix is based on the
     datasheet analysis.
   - Add a note mentioning that it has not been tested on real hardware.

 drivers/iio/temperature/tsys01.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iio/temperature/tsys01.c b/drivers/iio/temperature/tsys01.c
index 334bba6fdae6..104dd45598b0 100644
--- a/drivers/iio/temperature/tsys01.c
+++ b/drivers/iio/temperature/tsys01.c
@@ -119,7 +119,7 @@ static bool tsys01_crc_valid(u16 *n_prom)
 	u8 sum = 0;
 
 	for (cnt = 0; cnt < TSYS01_PROM_WORDS_NB; cnt++)
-		sum += ((n_prom[0] >> 8) + (n_prom[0] & 0xFF));
+		sum += ((n_prom[cnt] >> 8) + (n_prom[cnt] & 0xFF));
 
 	return (sum == 0);
 }
-- 
2.43.0

On Tue,  5 May 2026 08:10:24 +0100
Salah Triki <salah.triki@gmail.com> wrote:

> The current implementation of tsys01_crc_valid() incorrectly sums the
> first word (n_prom[0]) repeatedly instead of iterating over the 8 words
> retrieved from the PROM. This leads to a checksum mismatch and probe
> failure on hardware.
> 
> According to the TSYS01 datasheet, the PROM consists of 8 words. A valid
> check must iterate through all 8 words to verify the integrity of the
> calibration data. The current driver only checks the first word 8 times.
> 
> Note: This fix was identified during a code audit and is based on
> datasheet specifications. It has not been tested on real hardware.
> 
> Fixes: 43e53407f680 ("Add tsys01 meas-spec driver support")
> Signed-off-by: Salah Triki <salah.triki@gmail.com>
Bit of a gamble without testing but seems correct to me so small
gamble. Even taken it slow path doesn't really guarantee anyone will
happen to test it - so...

Applied to the fixes-togreg branch of iio.git and marked for stable.
> ---
> Changes in v2:
>    - Update commit message to clarify that the fix is based on the
>      datasheet analysis.
>    - Add a note mentioning that it has not been tested on real hardware.
> 
>  drivers/iio/temperature/tsys01.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/temperature/tsys01.c b/drivers/iio/temperature/tsys01.c
> index 334bba6fdae6..104dd45598b0 100644
> --- a/drivers/iio/temperature/tsys01.c
> +++ b/drivers/iio/temperature/tsys01.c
> @@ -119,7 +119,7 @@ static bool tsys01_crc_valid(u16 *n_prom)
>  	u8 sum = 0;
>  
>  	for (cnt = 0; cnt < TSYS01_PROM_WORDS_NB; cnt++)
> -		sum += ((n_prom[0] >> 8) + (n_prom[0] & 0xFF));
> +		sum += ((n_prom[cnt] >> 8) + (n_prom[cnt] & 0xFF));
>  
>  	return (sum == 0);
>  }