linux-kernel - Re: [PATCH] iio: accel: fxls8962af: Fix temperature calculation

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Message-ID: <aBPH2dHgwI_4lHvj@debian-BULLSEYE-live-builder-AMD64>
Date: Thu, 1 May 2025 16:13:29 -0300
From: Marcelo Schmitt <marcelo.schmitt1@...il.com>
To: Sean Nyekjaer <sean@...nix.com>
Cc: Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] iio: accel: fxls8962af: Fix temperature calculation

Hello Sean,

Overall, this looks good to me.
Only thing I think need to (not) change is the offset (see comment below).

Regards,
Marcelo

On 05/01, Sean Nyekjaer wrote:
> According to spec temperature should be returned in milli degrees Celsius.
> Add in_temp_scale to calculate from Celsius to milli Celsius.
> 
> Fixes: a3e0b51884ee ("iio: accel: add support for FXLS8962AF/FXLS8964AF accelerometers")
> Cc: stable@...r.kernel.org
> Signed-off-by: Sean Nyekjaer <sean@...nix.com>
> ---
>  drivers/iio/accel/fxls8962af-core.c | 17 ++++++++++++++---
...
>  
>  /* Raw temp channel offset */
> -#define FXLS8962AF_TEMP_CENTER_VAL		25
> +#define FXLS8962AF_TEMP_CENTER_VAL		25000
I think the offset was correct the way it was before.
For example, if the sensor at 37°C, the output code will be 0b00001100, 12 (decimal).
Then (_raw + _offset) * _scale = (12 + 25) * 1000 = 37000 milli °C

> +/* Raw temp channel scale */
> +#define FXLS8962AF_TEMP_SCALE			1000
>  
...
> @@ -736,6 +746,7 @@ static const struct iio_event_spec fxls8962af_event[] = {
>  	.type = IIO_TEMP, \
>  	.address = FXLS8962AF_TEMP_OUT, \
>  	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | \
> +			      BIT(IIO_CHAN_INFO_SCALE) | \
>  			      BIT(IIO_CHAN_INFO_OFFSET),\
>  	.scan_index = -1, \
>  	.scan_type = { \
Datasheet page 39 says 'the TEMP_OUT register contains the 8-bit, 2's complement
temperature value.'
So I think we can make the temperature scan element signed.
		.sign = 's',	\

Though, I guess that would be a thing for a separate patch.