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

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 27 Jul 2026 04:40:13 +0000
Yuanshen Cao <alex.caoys@gmail.com> wrote:

> 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@gmail.com> 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@gmail.com>  
> > 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.

I can't remember what the exact rules are for an Assisted tag but
to me it sounds fine to not have one here.

> 
> > 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")
Thanks.  Given it's ancient and Linus is getting fussier about
non critical bugs late in the cycle, I've queued this up for
the next merge window and marked it for stable rather than going
the quick route.

thanks,

Jonathan

> 
> 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@gmail.com>
> > >   
> >   
>