[PATCH AUTOSEL 4.19 12/12] hwmon: (scpi-hwmon) shows the negative temperature properly

[Sasha Levin <sashal@kernel.org>]

From: Riwen Lu <luriwen@kylinos.cn>

[ Upstream commit 78d13552346289bad4a9bf8eabb5eec5e5a321a5 ]

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>
Link: https://lore.kernel.org/r/20210604030959.736379-1-luriwen@kylinos.cn
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 7e49da50bc69..562f3e287297 100644
--- a/drivers/hwmon/scpi-hwmon.c
+++ b/drivers/hwmon/scpi-hwmon.c
@@ -107,6 +107,15 @@ 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);
 }
 
-- 
2.30.2