iio: imu: inv_icm42600: Fix temperature calculation

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

Posted by Sean Nyekjaer 9 months, 1 week ago

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>
---
 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,
-- 
Sean Nyekjaer <sean@geanix.com>

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

Posted by Jonathan Cameron 9 months, 1 week ago

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,