Re: [PATCH] iio: light: tsl2772: fix ALS calibscale readback

[Yuanshen Cao]

On Mon, Jul 27, 2026 at 03:14:07AM +0100, Jonathan Cameron wrote:
> On Fri, 24 Jul 2026 23:46:01 +0000
> Yuanshen Cao <alex.caoys@xxxxxxxxx> wrote:
> 
> > The read_raw() implementation uses IIO_LIGHT to distinguish between the
> > ambient light and proximity channels when handling
> > IIO_CHAN_INFO_CALIBSCALE.
> > 
> > However, the ALS channel is registered as IIO_INTENSITY, while
> > write_raw() correctly writes to IIO_INTENSITY. As a result, reading
> > in_intensity0_calibscale incorrectly returns the proximity gain instead
> > of the ALS gain.
> > 
> > This causes the following user-visible behavior:
> > - Writing in_intensity0_calibscale appears to have no effect because the
> >   readback reports the proximity gain.
> > - Writing in_proximity0_calibscale causes both in_proximity0_calibscale
> >   and in_intensity0_calibscale to report the same value.
> > 
> > Fix this by checking for IIO_INTENSITY in read_raw(), matching the
> > channel definition and the existing write_raw() implementation.
> > 
> > Signed-off-by: Yuanshen Cao <alex.caoys@xxxxxxxxx>
> Hi,
> 
> Fix looks good and the explanation correct.  Was this an AI found
> one, or did you either spot this whilst reading the code or best
> of all saw it in practice and went looking for what is wrong?

Hi Jonathan,

It's actually a bit of both. I first noticed the strange calibscale
behavior while testing a device with this sensor. Since most part of
this driver has been around for 7+ years, I wasn't expecting to find a
bug there. I asked ChatGPT for some ideas about what might explain the
behavior, and it pointed out the mismatch. I then went back and verified
it, and sure enough, it turned out to be a 14-year-old bug. After that,
I checked the rest of the file for similar issues, but this appears to
be the only instance. Also this was tested on the device and it works
as intended now.

> Give it is fix, what is missing is a suitable Fixes tag.
> Please see if you can figure out what that should be.
> No need to send a v2 unless anything else comes up in review.
> Just reply to this thread with the Fixes tag so I'll get it
> when I use b4 to pick up the patch

Thanks for pointing this out.
The missing tag is:

Fixes: 3c97c08b5735 ("iio: light: add TAOS tsl2x7x driver")

Best,

Yuanshen (Alex) Cao

> Thanks,
> 
> Jonathan
> 
> > ---
> >  drivers/iio/light/tsl2772.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iio/light/tsl2772.c b/drivers/iio/light/tsl2772.c
> > index 244f44379c36..2287585711c6 100644
> > --- a/drivers/iio/light/tsl2772.c
> > +++ b/drivers/iio/light/tsl2772.c
> > @@ -1274,7 +1274,7 @@ static int tsl2772_read_raw(struct iio_dev *indio_dev,
> >  		}
> >  		break;
> >  	case IIO_CHAN_INFO_CALIBSCALE:
> > -		if (chan->type == IIO_LIGHT)
> > +		if (chan->type == IIO_INTENSITY)
> >  			*val = tsl2772_als_gain[chip->settings.als_gain];
> >  		else
> >  			*val = tsl2772_prox_gain[chip->settings.prox_gain];
> > 
> > ---
> > base-commit: 1590cf0329716306e948a8fc29f1d3ee87d3989f
> > change-id: 20260724-tsl2772-calibscale-fix-0cc42518d5fc
> > 
> > Best regards,
> > --  
> > Yuanshen Cao <alex.caoys@xxxxxxxxx>
> > 
>