Re: [PATCH] iio: imu: inv_icm42600: Fix temperature calculation

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 4 May 2025 16:46:00 +0000
Jean-Baptiste Maneyrol <Jean-Baptiste.Maneyrol@tdk.com> wrote:

> Hello Sean, Jonathan,
> 
> good catch indeed!
> This is all good for me, thanks for your fix.
> 
> Acked-by: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>
> 
Applied.
> Best regards,
> JB
> 
> ________________________________________
> From: Jonathan Cameron <jic23@kernel.org>
> Sent: Sunday, May 4, 2025 17:28
> To: Sean Nyekjaer <sean@geanix.com>
> Cc: Jean-Baptiste Maneyrol <Jean-Baptiste.Maneyrol@tdk.com>; Lars-Peter Clausen <lars@metafoo.de>; Jean-Baptiste Maneyrol <Jean-Baptiste.Maneyrol@tdk.com>; Jonathan Cameron <Jonathan.Cameron@huawei.com>; linux-iio@vger.kernel.org <linux-iio@vger.kernel.org>; linux-kernel@vger.kernel.org <linux-kernel@vger.kernel.org>
> Subject: Re: [PATCH] iio: imu: inv_icm42600: Fix temperature calculation
>  
> This Message Is From an External Sender
> This message came from outside your organization.
>  
> On Fri, 02 May 2025 11:37:26 +0200
> Sean Nyekjaer <sean@geanix.com> wrote:
> 
> > From the documentation:
> > "offset to be added to <type>[Y]_raw prior toscaling by <type>[Y]_scale"
> > Offset should be applied before multiplying scale, so divide offset by
> > scale to make this correct.
> > 
> > Fixes: bc3eb0207fb5 ("iio: imu: inv_icm42600: add temperature sensor support")
> > Signed-off-by: Sean Nyekjaer <sean@geanix.com>  
> Looks correct to me.  Given this is going to have impacts on userspace
> I'd definitely like to know Jean-Baptiste has seen it though before I apply.
> So, Jean-Baptiste please take a look!
> 
> Thanks,
> 
> Jonathan
> 
> 
> > ---
> >  drivers/iio/imu/inv_icm42600/inv_icm42600_temp.c | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/iio/imu/inv_icm42600/inv_icm42600_temp.c b/drivers/iio/imu/inv_icm42600/inv_icm42600_temp.c
> > index 213cce1c31110e669e7191c8b42c9524c0d3e5db..91f0f381082bda3dbb95dfe1a38adcdc4eaf5419 100644
> > --- a/drivers/iio/imu/inv_icm42600/inv_icm42600_temp.c
> > +++ b/drivers/iio/imu/inv_icm42600/inv_icm42600_temp.c
> > @@ -67,16 +67,18 @@ int inv_icm42600_temp_read_raw(struct iio_dev *indio_dev,
> >  		return IIO_VAL_INT;
> >  	/*
> >  	 * T°C = (temp / 132.48) + 25
> > -	 * Tm°C = 1000 * ((temp * 100 / 13248) + 25)
> > +	 * Tm°C = 1000 * ((temp / 132.48) + 25)
> > +	 * Tm°C = 7.548309 * temp + 25000
> > +	 * Tm°C = (temp + 3312) * 7.548309
> >  	 * scale: 100000 / 13248 ~= 7.548309
> > -	 * offset: 25000
> > +	 * offset: 3312
> >  	 */
> >  	case IIO_CHAN_INFO_SCALE:
> >  		*val = 7;
> >  		*val2 = 548309;
> >  		return IIO_VAL_INT_PLUS_MICRO;
> >  	case IIO_CHAN_INFO_OFFSET:
> > -		*val = 25000;
> > +		*val = 3312;
> >  		return IIO_VAL_INT;
> >  	default:
> >  		return -EINVAL;
> > 
> > ---
> > base-commit: 609bc31eca06c7408e6860d8b46311ebe45c1fef
> > change-id: 20250502-imu-edc0faa6dae9
> > 
> > Best regards,  
>