[PATCH v3] hwmon: (scpi-hwmon) shows the negative temperature properly

[Riwen Lu <luriwen@kylinos.cn>]

The scpi hwmon shows the sub-zero temperature in an unsigned integer,
which would confuse the users when the machine works in low temperature
environment. This shows the sub-zero temperature in an signed value and
users can get it properly from sensors.

Signed-off-by: Riwen Lu <luriwen@kylinos.cn>
Tested-by: Xin Chen <chenxin@kylinos.cn>

---
Changes since v1:
- Add judgment for sensor->info.class. If it is TEMPERATURE situation,
  return the sensor value as a signed value, otherwise return it as a
  unsigned value.

Changes since v2:
- Add a typecast u64 to s64 when it is a temperature value.
- Add a comment ahead of the if statement.
- Remove the unnecessary 'else' statement.
---
 drivers/hwmon/scpi-hwmon.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/hwmon/scpi-hwmon.c b/drivers/hwmon/scpi-hwmon.c
index 25aac40f2764..919877970ae3 100644
--- a/drivers/hwmon/scpi-hwmon.c
+++ b/drivers/hwmon/scpi-hwmon.c
@@ -99,6 +99,15 @@ scpi_show_sensor(struct device *dev, struct device_attribute *attr, char *buf)
 
 	scpi_scale_reading(&value, sensor);
 
+	/*
+	 * Temperature sensor values are treated as signed values based on
+	 * observation even though that is not explicitly specified, and
+	 * because an unsigned u64 temperature does not really make practical
+	 * sense especially when the temperature is below zero degrees Celsius.
+	 */
+	if (sensor->info.class == TEMPERATURE)
+		return sprintf(buf, "%lld\n", (s64)value);
+
 	return sprintf(buf, "%llu\n", value);
 }
 
-- 
2.25.1


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