Re: [PATCH] iio: adc: pac1921: fix wrong channel used in trigger handler read

On Sun,  2 Aug 2026 14:12:46 +0700, Cong Nguyen <[email protected]> wrote:
> pac1921_trigger_handler() walks the enabled channels with
> iio_for_each_active_channel(), which yields the scan index (bit) of each
> active channel, while ch is a separate counter used to pack the samples
> contiguously into the scan buffer.
> 
> The register to read was looked up with the packing counter instead of
> the scan index:
> 
> 	ret = pac1921_read_res(priv, idev->channels[ch].address, &val);
> 
> pac1921_channels[] is ordered by scan index, so channels[bit] is the
> channel that is actually enabled, whereas channels[ch] is merely the
> ch-th array entry. These coincide only when the enabled channels form a
> contiguous prefix (e.g. all channels enabled). With a sparse scan mask -
> for example when only the power channel (scan index 3) is enabled - the
> handler reads the wrong register (VBUS instead of VPOWER) and pushes it
> to userspace as the enabled channel's data.
> 
> Index the channel array by the scan index (bit) to read the correct
> register, keeping ch only for contiguous packing into the scan buffer.
> 
> Fixes: 371f778b83cd ("iio: adc: add support for pac1921")
> Cc: [email protected]
> Assisted-by: Claude:claude-opus-4
> Signed-off-by: Cong Nguyen <[email protected]>
> ---
>  drivers/iio/adc/pac1921.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/pac1921.c b/drivers/iio/adc/pac1921.c
> index bce7185953ec..0037509503ed 100644
> --- a/drivers/iio/adc/pac1921.c
> +++ b/drivers/iio/adc/pac1921.c
> @@ -1037,7 +1037,7 @@ static irqreturn_t pac1921_trigger_handler(int irq, void *p)
>  	iio_for_each_active_channel(idev, bit) {
>  		u16 val;
>  
> -		ret = pac1921_read_res(priv, idev->channels[ch].address, &val);
> +		ret = pac1921_read_res(priv, idev->channels[bit].address, &val);
>  		if (ret)
>  			goto done;
>  
> -- 
> 2.25.1
> 

This looks correct to me. I guess I didn't test it properly with a subset of
enabled channels when I wrote this.
Thanks for the fix!

Acked-by: Matteo Martelli <[email protected]>