Re: [PATCH 1/2] hwmon: (cros_ec) Implement custom kelvin to celsius conversions

[Guenter Roeck]

On Tue, Jun 30, 2026 at 10:57:51PM +0200, Thomas Weißschuh wrote:
> The ChromeOS EC APIs use integers representing degrees kelvin for
> temperatures. The default conversions from linux/units.h will then
> always convert these integer degrees celsius with a 150 millidegree
> offset. This is a bit confusing, as it also differs from other CrOS EC
> tooling. Internally the EC uses a kelvin to celsius offset of a round
> 273, so the current conversion is also not entirely accurate.
> 
> Implement a custom conversion which preserves round values.
> 
> Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>

Applied.

Thanks,
Guenter

> ---
>  drivers/hwmon/cros_ec_hwmon.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwmon/cros_ec_hwmon.c b/drivers/hwmon/cros_ec_hwmon.c
> index ea24056ae646..44291799dd8e 100644
> --- a/drivers/hwmon/cros_ec_hwmon.c
> +++ b/drivers/hwmon/cros_ec_hwmon.c
> @@ -147,9 +147,17 @@ static bool cros_ec_hwmon_is_error_temp(u8 temp)
>  	       temp == EC_TEMP_SENSOR_NOT_CALIBRATED;
>  }
>  
> +/* This differs slightly from the variant in units.h to avoid rounding inconsistencies. */
> +#define CROS_EC_HWMON_ABSOLUTE_ZERO_MILLICELSIUS (-273000)
> +
> +static long cros_ec_hwmon_kelvin_to_millicelsius(long t)
> +{
> +	return t * MILLIDEGREE_PER_DEGREE + CROS_EC_HWMON_ABSOLUTE_ZERO_MILLICELSIUS;
> +}
> +
>  static long cros_ec_hwmon_temp_to_millicelsius(u8 temp)
>  {
> -	return kelvin_to_millicelsius((((long)temp) + EC_TEMP_SENSOR_OFFSET));
> +	return cros_ec_hwmon_kelvin_to_millicelsius((((long)temp) + EC_TEMP_SENSOR_OFFSET));
>  }
>  
>  static bool cros_ec_hwmon_attr_is_temp_threshold(u32 attr)
> @@ -228,7 +236,7 @@ static int cros_ec_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
>  								cros_ec_hwmon_attr_to_thres(attr),
>  								&threshold);
>  			if (ret == 0)
> -				*val = kelvin_to_millicelsius(threshold);
> +				*val = cros_ec_hwmon_kelvin_to_millicelsius(threshold);
>  		}
>  	}
>