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.
> 
> > 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")

That's not the patch title. Unfortunately I missed running a
check on this and it surfaced in linux-next forcing a rebase of
the IIO tree to repair things.

It's an ancient commit and the title didn't follow modern conventions

staging: iio: add TAOS tsl2x7x driver

Anyhow fixed up now

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>
> > >   
> >   
>