linux-kernel - Re: [PATCH v2 3/3] iio: temperature: mlx90632 Change return value of sensor measurement channel

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Date:   Sun, 4 Sep 2022 16:56:34 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Crt Mori <cmo@...exis.com>
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH v2 3/3] iio: temperature: mlx90632 Change return value
 of sensor measurement channel

On Sun, 4 Sep 2022 17:27:28 +0200
Crt Mori <cmo@...exis.com> wrote:

> On Sun, 4 Sept 2022 at 17:23, Jonathan Cameron <jic23@...nel.org> wrote:
> >
> > On Sun,  4 Sep 2022 00:24:22 +0200
> > cmo@...exis.com wrote:
> >  
> > > From: Crt Mori <cmo@...exis.com>
> > >
> > > The current EINVAL value is more applicable to embedded library, where
> > > user can actually put the fixed value to the sensor. In case of the
> > > driver if the value of the channel is invalid it is better in inform
> > > userspace that Channel was out of range as that implies more to internal
> > > driver error than invalid input. It also makes for easier debugging of
> > > where the error comes from during the development.
> > >
> > > Signed-off-by: Crt Mori <cmo@...exis.com>  
> > Hmm. That's an obscure return value - I think it's mostly going to confuse
> > anyone who ever gets it.  So not sure this change is wise even though the
> > descriptive text for that one does seem very much suited to this usecase.
> >  
> I did get it few times during the development due to read when sensor
> is not busy, but the measurement data not yet updated correctly due to
> powermode switch. I think I added enough delays all around to avoid
> hitting it and with proper power mode switching, but there might be a
> case, so it will be easier to spot in the source code in future. I
> would not remove it, if that is what you are proposing.

I meant leave it as EINVAL. The users of ECHRNG are very very
few in number, so I don't have a good understanding of it's expected
uses.. 
> 
> > > ---
> > >  drivers/iio/temperature/mlx90632.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/iio/temperature/mlx90632.c b/drivers/iio/temperature/mlx90632.c
> > > index 37edd324d6a1..d511d36942d3 100644
> > > --- a/drivers/iio/temperature/mlx90632.c
> > > +++ b/drivers/iio/temperature/mlx90632.c
> > > @@ -435,7 +435,7 @@ static int mlx90632_channel_new_select(int perform_ret, uint8_t *channel_new,
> > >               *channel_old = 1;
> > >               break;
> > >       default:
> > > -             return -EINVAL;
> > > +             return -ECHRNG;
> > >       }
> > >
> > >       return 0;  
> >