Re: [PATCH] iio: temperature: tmp006: Fix endianness byte swap in trigger handler

[Joshua Crofts]

On Mon,  7 Sep 2026 09:22:15 +0100
Salah Triki <salah.triki@xxxxxxxxx> wrote:

> In tmp006_trigger_handler(), i2c_smbus_read_word_data() is used to read
> the VOBJECT and TAMBIENT registers. However, the TMP006 stores register
> values in Big Endian byte order, while i2c_smbus_read_word_data() assumes
> Little Endian.
> 
> This causes byte-swapped values to be pushed to the IIO buffer on Little
> Endian architectures, leading to corrupted sensor readings when using
> triggered buffers.
> 
> Fix this by switching to i2c_smbus_read_word_swapped() inside the trigger
> handler.
> 
> Fixes: 91f75ccf9f03 ("iio: temperature: tmp006: add triggered buffer support")
> Assisted-by: LLM
> Signed-off-by: Salah Triki <salah.triki@xxxxxxxxx>
> ---
>  drivers/iio/temperature/tmp006.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/temperature/tmp006.c b/drivers/iio/temperature/tmp006.c
> index d9f6449ec0d8..f3b3de0bf221 100644
> --- a/drivers/iio/temperature/tmp006.c
> +++ b/drivers/iio/temperature/tmp006.c
> @@ -256,12 +256,12 @@ static irqreturn_t tmp006_trigger_handler(int irq, void *p)
>  	} scan = { };
>  	s32 ret;
>  
> -	ret = i2c_smbus_read_word_data(data->client, TMP006_VOBJECT);
> +	ret = i2c_smbus_read_word_swapped(data->client, TMP006_VOBJECT);

Sashiko has something to say:

Does this code introduce a regression where sensor readings are corrupted for
userspace clients reading from the triggered IIO buffer on Little Endian
architectures?

Before this patch, i2c_smbus_read_word_data() returned a byte-swapped word.
When this was assigned to the s16 array in tmp006_trigger_handler() on a Little
Endian CPU, the memory layout became [msb, lsb]. This implicitly matched the
IIO_BE (Big Endian) endianness declared in the tmp006_channels array, so it
worked correctly.

By switching to i2c_smbus_read_word_swapped(), the value is now in native CPU
endianness [lsb, msb]. However, the channel specification in tmp006_channels
still specifies IIO_BE:
drivers/iio/temperature/tmp006.c:tmp006_channels[] {
    ...
        .scan_type = {
            .endianness = IIO_BE,
        },
    ...
}

Because the ABI still advertises the data as Big Endian, userspace will parse
the little-endian data as big-endian.

Should the channel specification be updated from IIO_BE to IIO_CPU, or should
scan.channels be declared as __be16 and populated using cpu_to_be16() to
preserve the existing Big Endian ABI?

-- 
Kind regards,
Joshua Crofts