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hwmon: (cros_ec) Implement custom kelvin to celsius conversions

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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@weissschuh.net>
Link: https://lore.kernel.org/r/20260630-cros_ec-hwmon-overflow-v1-1-3d2ecd3eb0f2@weissschuh.net
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Thomas Weißschuh 2026-06-30 22:57:51 +02:00 committed by Guenter Roeck
parent ecc0eb5e95
commit de0181c95b
1 changed files with 10 additions and 2 deletions
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12
drivers/hwmon/cros_ec_hwmon.c
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@ -146,9 +146,17 @@ 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)
@ -227,7 +235,7 @@ 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);
}
}